-When PCRE2 is built with Unicode support (the default), the Unicode properties -of all characters can be tested with \p and \P, or, alternatively, the +When PCRE2 is built with Unicode support (the default), certain Unicode +character properties can be tested with \p and \P, or, alternatively, the PCRE2_UCP option can be set when a pattern is compiled; this causes \w and friends to use Unicode property support instead of the built-in tables. PCRE2_UCP also causes upper/lower casing operations on characters with code @@ -4018,7 +4018,7 @@ Cambridge, England.
-Last updated: 30 November 2021
+Last updated: 08 December 2021
Copyright © 1997-2021 University of Cambridge.
diff --git a/doc/html/pcre2build.html b/doc/html/pcre2build.html
index a1c2e95..0c5635a 100644
--- a/doc/html/pcre2build.html
+++ b/doc/html/pcre2build.html
@@ -142,8 +142,9 @@ locked this out by setting PCRE2_NEVER_UTF.
UTF support allows the libraries to process character code points up to
0x10ffff in the strings that they handle. Unicode support also gives access to
the Unicode properties of characters, using pattern escapes such as \P, \p,
-and \X. Only the general category properties such as Lu and Nd are
-supported. Details are given in the
+and \X. Only the general category properties such as Lu and Nd,
+script names, and some bi-directional properties are supported. Details are
+given in the
pcre2pattern
documentation.
-Last updated: 20 March 2020
+Last updated: 08 December 2021
-Copyright © 1997-2020 University of Cambridge.
+Copyright © 1997-2021 University of Cambridge.
Return to the PCRE2 index page.
diff --git a/doc/html/pcre2compat.html b/doc/html/pcre2compat.html
index 6bd4cf0..5f390c1 100644
--- a/doc/html/pcre2compat.html
+++ b/doc/html/pcre2compat.html
@@ -66,9 +66,9 @@ interprets them.
6. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is
built with Unicode support (the default). The properties that can be tested
with \p and \P are limited to the general category properties such as Lu and
-Nd, script names such as Greek or Han, and the derived properties Any and L&.
-Both PCRE2 and Perl support the Cs (surrogate) property, but in PCRE2 its use
-is limited. See the
+Nd, script names such as Greek or Han, Bidi_Class, Bidi_Control, and the
+derived properties Any and LC (synonym L&). Both PCRE2 and Perl support the Cs
+(surrogate) property, but in PCRE2 its use is limited. See the
pcre2pattern
documentation for details. The long synonyms for property names that Perl
supports (such as \p{Letter}) are not supported by PCRE2, nor is it permitted
@@ -257,7 +257,7 @@ Cambridge, England.
REVISION
-Last updated: 01 December 2021
+Last updated: 08 December 2021
Copyright © 1997-2021 University of Cambridge.
diff --git a/doc/html/pcre2pattern.html b/doc/html/pcre2pattern.html
index 6afaf27..ae2ba87 100644
--- a/doc/html/pcre2pattern.html
+++ b/doc/html/pcre2pattern.html
@@ -783,11 +783,13 @@ escape sequences are:
\P{xx} a character without the xx property
\X a Unicode extended grapheme cluster
-The property names represented by xx above are case-sensitive. There is
-support for Unicode script names, Unicode general category properties, "Any",
-which matches any character (including newline), and some special PCRE2
-properties (described in the
-next section).
+The property names represented by xx above are not case-sensitive, and in
+accordance with Unicode's "loose matching" rules, spaces, hyphens, and
+underscores are ignored. There is support for Unicode script names, Unicode
+general category properties, "Any", which matches any character (including
+newline), Bidi_Control, Bidi_Class, and some special PCRE2 properties
+(described
+below).
Other Perl properties such as "InMusicalSymbols" are not supported by PCRE2.
Note that \P{Any} does not match any characters, so always causes a match
failure.
@@ -1030,9 +1032,9 @@ The following general category property codes are supported:
Zp Paragraph separator
Zs Space separator
-The special property L& is also supported: it matches a character that has
-the Lu, Ll, or Lt property, in other words, a letter that is not classified as
-a modifier or "other".
+The special property LC, which has the synonym L&, is also supported: it
+matches a character that has the Lu, Ll, or Lt property, in other words, a
+letter that is not classified as a modifier or "other".
The Cs (Surrogate) property applies only to characters whose code points are in @@ -1067,6 +1069,45 @@ properties in PCRE2 by default, though you can make them do so by setting the PCRE2_UCP option or by starting the pattern with (*UCP).
+Two properties relating to bi-directional text are supported: +
+ \p{Bidi_Control} matches a Bidi control character
+ \p{Bidi_Class:<class>} matches a character with the given class
+
+The recognized classes are:
++ AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space ++For Bidi_Class, an equals sign may be used instead of a colon. The class names +are case-insensitive. As for other properties, only the short names are +recognized. + +
@@ -3861,7 +3902,7 @@ Cambridge, England.
-Last updated: 01 December 2021
+Last updated: 08 December 2021
Copyright © 1997-2021 University of Cambridge.
diff --git a/doc/html/pcre2syntax.html b/doc/html/pcre2syntax.html
index 735eb69..124a3f1 100644
--- a/doc/html/pcre2syntax.html
+++ b/doc/html/pcre2syntax.html
@@ -20,28 +20,29 @@ please consult the man page, in case the conversion went wrong.
@@ -362,7 +363,40 @@ Yezidi, Yi, Zanabazar_Square.
-+
+ \p{Bidi_Control} matches a Bidi control character
+ \p{Bidi_Class:<class>} matches a character with the given class
+
+The recognized classes are:
++ AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space ++ +
[...] positive character class @@ -390,7 +424,7 @@ In PCRE2, POSIX character set names recognize only ASCII characters by default, but some of them use Unicode properties if PCRE2_UCP is set. You can use \Q...\E inside a character class. -
QUANTIFIERS
+
QUANTIFIERS
? 0 or 1, greedy @@ -411,7 +445,7 @@ but some of them use Unicode properties if PCRE2_UCP is set. You can use {n,}? n or more, lazy-
ANCHORS AND SIMPLE ASSERTIONS
+
ANCHORS AND SIMPLE ASSERTIONS
\b word boundary @@ -429,7 +463,7 @@ but some of them use Unicode properties if PCRE2_UCP is set. You can use \G first matching position in subject-
REPORTED MATCH POINT SETTING
+
REPORTED MATCH POINT SETTING
\K set reported start of match @@ -439,13 +473,13 @@ for compatibility with Perl. However, if the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option is set, the previous behaviour is re-enabled. When this option is set, \K is honoured in positive assertions, but ignored in negative ones. --
ALTERNATION
+
ALTERNATION
expr|expr|expr...-
CAPTURING
+
CAPTURING
(...) capture group @@ -460,20 +494,20 @@ In non-UTF modes, names may contain underscores and ASCII letters and digits; in UTF modes, any Unicode letters and Unicode decimal digits are permitted. In both cases, a name must not start with a digit. --
ATOMIC GROUPS
+
ATOMIC GROUPS
(?>...) atomic non-capture group (*atomic:...) atomic non-capture group-
COMMENT
+
COMMENT
(?#....) comment (not nestable)-
OPTION SETTING
+
OPTION SETTING
Changes of these options within a group are automatically cancelled at the end of the group. @@ -518,7 +552,7 @@ not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. The application can lock out the use of (*UTF) and (*UCP) by setting the PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time.
-
NEWLINE CONVENTION
+
NEWLINE CONVENTION
These are recognized only at the very start of the pattern or after option settings with a similar syntax. @@ -531,7 +565,7 @@ settings with a similar syntax. (*NUL) the NUL character (binary zero)
WHAT \R MATCHES
+
WHAT \R MATCHES
These are recognized only at the very start of the pattern or after option setting with a similar syntax. @@ -540,7 +574,7 @@ setting with a similar syntax. (*BSR_UNICODE) any Unicode newline sequence
LOOKAHEAD AND LOOKBEHIND ASSERTIONS
+
LOOKAHEAD AND LOOKBEHIND ASSERTIONS
(?=...) ) @@ -561,7 +595,7 @@ setting with a similar syntax.Each top-level branch of a lookbehind must be of a fixed length. -
NON-ATOMIC LOOKAROUND ASSERTIONS
+
NON-ATOMIC LOOKAROUND ASSERTIONS
These assertions are specific to PCRE2 and are not Perl-compatible.
@@ -574,7 +608,7 @@ These assertions are specific to PCRE2 and are not Perl-compatible. (*non_atomic_positive_lookbehind:...) )-
SCRIPT RUNS
+
SCRIPT RUNS
(*script_run:...) ) script run, can be backtracked into @@ -584,7 +618,7 @@ These assertions are specific to PCRE2 and are not Perl-compatible. (*asr:...) )-
BACKREFERENCES
+
BACKREFERENCES
\n reference by number (can be ambiguous) @@ -601,7 +635,7 @@ These assertions are specific to PCRE2 and are not Perl-compatible. (?P=name) reference by name (Python)-
SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
+
SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
(?R) recurse whole pattern @@ -620,7 +654,7 @@ These assertions are specific to PCRE2 and are not Perl-compatible. \g'-n' call subroutine by relative number (PCRE2 extension)-
CONDITIONAL PATTERNS
+
CONDITIONAL PATTERNS
(?(condition)yes-pattern) @@ -643,7 +677,7 @@ Note the ambiguity of (?(R) and (?(Rn) which might be named reference conditions or recursion tests. Such a condition is interpreted as a reference condition if the relevant named group exists. -
BACKTRACKING CONTROL
+
BACKTRACKING CONTROL
All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) the name is mandatory, for the others it is optional. (*SKIP) changes its behaviour @@ -670,7 +704,7 @@ pattern is not anchored. The effect of one of these verbs in a group called as a subroutine is confined to the subroutine call.
-
CALLOUTS
+
CALLOUTS
(?C) callout (assumed number 0) @@ -681,12 +715,12 @@ The allowed string delimiters are ` ' " ^ % # $ (which are the same for the start and the end), and the starting delimiter { matched with the ending delimiter }. To encode the ending delimiter within the string, double it. -
SEE ALSO
+
SEE ALSO
pcre2pattern(3), pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2(3).
-
AUTHOR
+
AUTHOR
Philip Hazel
-
@@ -695,9 +729,9 @@ Retired from University Computing Service Cambridge, England.
REVISION
+
REVISION
-Last updated: 30 August 2021 +Last updated: 08 December 2021
@@ -486,9 +486,9 @@ Cambridge, England. REVISION
Copyright © 1997-2021 University of Cambridge.
diff --git a/doc/html/pcre2unicode.html b/doc/html/pcre2unicode.html index 76ca6ea..defb46f 100644 --- a/doc/html/pcre2unicode.html +++ b/doc/html/pcre2unicode.html @@ -52,13 +52,13 @@ When PCRE2 is built with Unicode support, the escape sequences \p{..}, \P{..}, and \X can be used. This is not dependent on the PCRE2_UTF setting. The Unicode properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal number, the -Unicode script names such as Arabic or Han, and the derived properties Any and -L&. Full lists are given in the +Unicode script names such as Arabic or Han, Bidi_Class, Bidi_Control, and the +derived properties Any and LC (synonym L&). Full lists are given in the pcre2pattern and pcre2syntax documentation. Only the short names for properties are supported. For example, -\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported. +\p{L} matches a letter. Its longer synonym, \p{Letter}, is not supported. Furthermore, in Perl, many properties may optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE2 does not support this.
-Last updated: 23 February 2020 +Last updated: 08 December 2021
-Copyright © 1997-2020 University of Cambridge. +Copyright © 1997-2021 University of Cambridge.
Return to the PCRE2 index page. diff --git a/doc/pcre2.txt b/doc/pcre2.txt index 103cb97..ebf43a5 100644 --- a/doc/pcre2.txt +++ b/doc/pcre2.txt @@ -2012,13 +2012,13 @@ LOCALE SUPPORT code points are less than 256. By default, higher-valued code points never match escapes such as \w or \d. - When PCRE2 is built with Unicode support (the default), the Unicode - properties of all characters can be tested with \p and \P, or, alterna- - tively, the PCRE2_UCP option can be set when a pattern is compiled; - this causes \w and friends to use Unicode property support instead of - the built-in tables. PCRE2_UCP also causes upper/lower casing opera- - tions on characters with code points greater than 127 to use Unicode - properties. These effects apply even when PCRE2_UTF is not set. + When PCRE2 is built with Unicode support (the default), certain Unicode + character properties can be tested with \p and \P, or, alternatively, + the PCRE2_UCP option can be set when a pattern is compiled; this causes + \w and friends to use Unicode property support instead of the built-in + tables. PCRE2_UCP also causes upper/lower casing operations on charac- + ters with code points greater than 127 to use Unicode properties. These + effects apply even when PCRE2_UTF is not set. The use of locales with Unicode is discouraged. If you are handling characters with code points greater than 127, you should either use @@ -3857,7 +3857,7 @@ AUTHOR REVISION - Last updated: 30 November 2021 + Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ @@ -3970,8 +3970,8 @@ UNICODE AND UTF SUPPORT 0x10ffff in the strings that they handle. Unicode support also gives access to the Unicode properties of characters, using pattern escapes such as \P, \p, and \X. Only the general category properties such as Lu - and Nd are supported. Details are given in the pcre2pattern documenta- - tion. + and Nd, script names, and some bi-directional properties are supported. + Details are given in the pcre2pattern documentation. Pattern escapes such as \d and \w do not by default make use of Unicode properties. The application can request that they do by setting the @@ -4453,8 +4453,8 @@ AUTHOR REVISION - Last updated: 20 March 2020 - Copyright (c) 1997-2020 University of Cambridge. + Last updated: 08 December 2021 + Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ @@ -4941,20 +4941,21 @@ DIFFERENCES BETWEEN PCRE2 AND PERL 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is built with Unicode support (the default). The properties that can be tested with \p and \P are limited to the general category properties - such as Lu and Nd, script names such as Greek or Han, and the derived - properties Any and L&. Both PCRE2 and Perl support the Cs (surrogate) - property, but in PCRE2 its use is limited. See the pcre2pattern docu- - mentation for details. The long synonyms for property names that Perl - supports (such as \p{Letter}) are not supported by PCRE2, nor is it - permitted to prefix any of these properties with "Is". + such as Lu and Nd, script names such as Greek or Han, Bidi_Class, + Bidi_Control, and the derived properties Any and LC (synonym L&). Both + PCRE2 and Perl support the Cs (surrogate) property, but in PCRE2 its + use is limited. See the pcre2pattern documentation for details. The + long synonyms for property names that Perl supports (such as \p{Let- + ter}) are not supported by PCRE2, nor is it permitted to prefix any of + these properties with "Is". 7. PCRE2 supports the \Q...\E escape for quoting substrings. Characters in between are treated as literals. However, this is slightly different - from Perl in that $ and @ are also handled as literals inside the + from Perl in that $ and @ are also handled as literals inside the quotes. In Perl, they cause variable interpolation (PCRE2 does not have variables). Also, Perl does "double-quotish backslash interpolation" on - any backslashes between \Q and \E which, its documentation says, "may - lead to confusing results". PCRE2 treats a backslash between \Q and \E + any backslashes between \Q and \E which, its documentation says, "may + lead to confusing results". PCRE2 treats a backslash between \Q and \E just like any other character. Note the following examples: Pattern PCRE2 matches Perl matches @@ -4966,133 +4967,133 @@ DIFFERENCES BETWEEN PCRE2 AND PERL \QA\B\E A\B A\B \Q\\E \ \\E - The \Q...\E sequence is recognized both inside and outside character + The \Q...\E sequence is recognized both inside and outside character classes by both PCRE2 and Perl. - 8. Fairly obviously, PCRE2 does not support the (?{code}) and + 8. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code}) constructions. However, PCRE2 does have a "callout" feature, which allows an external function to be called during pattern matching. See the pcre2callout documentation for details. - 9. Subroutine calls (whether recursive or not) were treated as atomic - groups up to PCRE2 release 10.23, but from release 10.30 this changed, + 9. Subroutine calls (whether recursive or not) were treated as atomic + groups up to PCRE2 release 10.23, but from release 10.30 this changed, and backtracking into subroutine calls is now supported, as in Perl. - 10. In PCRE2, if any of the backtracking control verbs are used in a - group that is called as a subroutine (whether or not recursively), - their effect is confined to that group; it does not extend to the sur- - rounding pattern. This is not always the case in Perl. In particular, - if (*THEN) is present in a group that is called as a subroutine, its + 10. In PCRE2, if any of the backtracking control verbs are used in a + group that is called as a subroutine (whether or not recursively), + their effect is confined to that group; it does not extend to the sur- + rounding pattern. This is not always the case in Perl. In particular, + if (*THEN) is present in a group that is called as a subroutine, its action is limited to that group, even if the group does not contain any - | characters. Note that such groups are processed as anchored at the + | characters. Note that such groups are processed as anchored at the point where they are tested. - 11. If a pattern contains more than one backtracking control verb, the - first one that is backtracked onto acts. For example, in the pattern - A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure + 11. If a pattern contains more than one backtracking control verb, the + first one that is backtracked onto acts. For example, in the pattern + A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases it is the same as PCRE2, but there are cases where it differs. - 12. There are some differences that are concerned with the settings of - captured strings when part of a pattern is repeated. For example, - matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 un- + 12. There are some differences that are concerned with the settings of + captured strings when part of a pattern is repeated. For example, + matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 un- set, but in PCRE2 it is set to "b". - 13. PCRE2's handling of duplicate capture group numbers and names is - not as general as Perl's. This is a consequence of the fact the PCRE2 - works internally just with numbers, using an external table to trans- - late between numbers and names. In particular, a pattern such as - (?|(?A)|(?B)), where the two capture groups have the same number - but different names, is not supported, and causes an error at compile + 13. PCRE2's handling of duplicate capture group numbers and names is + not as general as Perl's. This is a consequence of the fact the PCRE2 + works internally just with numbers, using an external table to trans- + late between numbers and names. In particular, a pattern such as + (?|(?A)|(?B)), where the two capture groups have the same number + but different names, is not supported, and causes an error at compile time. If it were allowed, it would not be possible to distinguish which - group matched, because both names map to capture group number 1. To + group matched, because both names map to capture group number 1. To avoid this confusing situation, an error is given at compile time. 14. Perl used to recognize comments in some places that PCRE2 does not, - for example, between the ( and ? at the start of a group. If the /x - modifier is set, Perl allowed white space between ( and ? though the - latest Perls give an error (for a while it was just deprecated). There + for example, between the ( and ? at the start of a group. If the /x + modifier is set, Perl allowed white space between ( and ? though the + latest Perls give an error (for a while it was just deprecated). There may still be some cases where Perl behaves differently. - 15. Perl, when in warning mode, gives warnings for character classes - such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter- + 15. Perl, when in warning mode, gives warnings for character classes + such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter- als. PCRE2 has no warning features, so it gives an error in these cases because they are almost certainly user mistakes. - 16. In PCRE2, the upper/lower case character properties Lu and Ll are - not affected when case-independent matching is specified. For example, + 16. In PCRE2, the upper/lower case character properties Lu and Ll are + not affected when case-independent matching is specified. For example, \p{Lu} always matches an upper case letter. I think Perl has changed in - this respect; in the release at the time of writing (5.34), \p{Lu} and + this respect; in the release at the time of writing (5.34), \p{Lu} and \p{Ll} match all letters, regardless of case, when case independence is specified. 17. From release 5.32.0, Perl locks out the use of \K in lookaround as- - sertions. From release 10.38 PCRE2 does the same by default. However, - there is an option for re-enabling the previous behaviour. When this - option is set, \K is acted on when it occurs in positive assertions, + sertions. From release 10.38 PCRE2 does the same by default. However, + there is an option for re-enabling the previous behaviour. When this + option is set, \K is acted on when it occurs in positive assertions, but is ignored in negative assertions. - 18. PCRE2 provides some extensions to the Perl regular expression fa- - cilities. Perl 5.10 included new features that were not in earlier - versions of Perl, some of which (such as named parentheses) were in + 18. PCRE2 provides some extensions to the Perl regular expression fa- + cilities. Perl 5.10 included new features that were not in earlier + versions of Perl, some of which (such as named parentheses) were in PCRE2 for some time before. This list is with respect to Perl 5.34: - (a) Although lookbehind assertions in PCRE2 must match fixed length + (a) Although lookbehind assertions in PCRE2 must match fixed length strings, each alternative toplevel branch of a lookbehind assertion can - match a different length of string. Perl used to require them all to - have the same length, but the latest version has some variable length + match a different length of string. Perl used to require them all to + have the same length, but the latest version has some variable length support. (b) From PCRE2 10.23, backreferences to groups of fixed length are sup- - ported in lookbehinds, provided that there is no possibility of refer- - encing a non-unique number or name. Perl does not support backrefer- + ported in lookbehinds, provided that there is no possibility of refer- + encing a non-unique number or name. Perl does not support backrefer- ences in lookbehinds. - (c) If PCRE2_DOLLAR_ENDONLY is set and PCRE2_MULTILINE is not set, the + (c) If PCRE2_DOLLAR_ENDONLY is set and PCRE2_MULTILINE is not set, the $ meta-character matches only at the very end of the string. - (d) A backslash followed by a letter with no special meaning is + (d) A backslash followed by a letter with no special meaning is faulted. (Perl can be made to issue a warning.) - (e) If PCRE2_UNGREEDY is set, the greediness of the repetition quanti- + (e) If PCRE2_UNGREEDY is set, the greediness of the repetition quanti- fiers is inverted, that is, by default they are not greedy, but if fol- lowed by a question mark they are. - (f) PCRE2_ANCHORED can be used at matching time to force a pattern to + (f) PCRE2_ANCHORED can be used at matching time to force a pattern to be tried only at the first matching position in the subject string. - (g) The PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY and + (g) The PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY and PCRE2_NOTEMPTY_ATSTART options have no Perl equivalents. - (h) The \R escape sequence can be restricted to match only CR, LF, or + (h) The \R escape sequence can be restricted to match only CR, LF, or CRLF by the PCRE2_BSR_ANYCRLF option. - (i) The callout facility is PCRE2-specific. Perl supports codeblocks + (i) The callout facility is PCRE2-specific. Perl supports codeblocks and variable interpolation, but not general hooks on every match. (j) The partial matching facility is PCRE2-specific. - (k) The alternative matching function (pcre2_dfa_match() matches in a + (k) The alternative matching function (pcre2_dfa_match() matches in a different way and is not Perl-compatible. - (l) PCRE2 recognizes some special sequences such as (*CR) or (*NO_JIT) - at the start of a pattern. These set overall options that cannot be + (l) PCRE2 recognizes some special sequences such as (*CR) or (*NO_JIT) + at the start of a pattern. These set overall options that cannot be changed within the pattern. - (m) PCRE2 supports non-atomic positive lookaround assertions. This is + (m) PCRE2 supports non-atomic positive lookaround assertions. This is an extension to the lookaround facilities. The default, Perl-compatible lookarounds are atomic. - 19. The Perl /a modifier restricts /d numbers to pure ascii, and the - /aa modifier restricts /i case-insensitive matching to pure ascii, ig- - noring Unicode rules. This separation cannot be represented with + 19. The Perl /a modifier restricts /d numbers to pure ascii, and the + /aa modifier restricts /i case-insensitive matching to pure ascii, ig- + noring Unicode rules. This separation cannot be represented with PCRE2_UCP. 20. Perl has different limits than PCRE2. See the pcre2limit documenta- tion for details. Perl went with 5.10 from recursion to iteration keep- ing the intermediate matches on the heap, which is ~10% slower but does - not fall into any stack-overflow limit. PCRE2 made a similar change at - release 10.30, and also has many build-time and run-time customizable + not fall into any stack-overflow limit. PCRE2 made a similar change at + release 10.30, and also has many build-time and run-time customizable limits. @@ -5105,7 +5106,7 @@ AUTHOR REVISION - Last updated: 01 December 2021 + Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ @@ -6894,16 +6895,17 @@ BACKSLASH \P{xx} a character without the xx property \X a Unicode extended grapheme cluster - The property names represented by xx above are case-sensitive. There is - support for Unicode script names, Unicode general category properties, - "Any", which matches any character (including newline), and some spe- - cial PCRE2 properties (described in the next section). Other Perl - properties such as "InMusicalSymbols" are not supported by PCRE2. Note - that \P{Any} does not match any characters, so always causes a match - failure. + The property names represented by xx above are not case-sensitive, and + in accordance with Unicode's "loose matching" rules, spaces, hyphens, + and underscores are ignored. There is support for Unicode script names, + Unicode general category properties, "Any", which matches any character + (including newline), Bidi_Control, Bidi_Class, and some special PCRE2 + properties (described below). Other Perl properties such as "InMusi- + calSymbols" are not supported by PCRE2. Note that \P{Any} does not + match any characters, so always causes a match failure. Sets of Unicode characters are defined as belonging to certain scripts. - A character from one of these sets can be matched using a script name. + A character from one of these sets can be matched using a script name. For example: \p{Greek} @@ -6911,44 +6913,44 @@ BACKSLASH Unassigned characters (and in non-UTF 32-bit mode, characters with code points greater than 0x10FFFF) are assigned the "Unknown" script. Others - that are not part of an identified script are lumped together as "Com- + that are not part of an identified script are lumped together as "Com- mon". The current list of scripts is: - Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- - nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, - Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- - nian, Chakma, Cham, Cherokee, Chorasmian, Common, Coptic, Cuneiform, - Cypriot, Cypro_Minoan, Cyrillic, Deseret, Devanagari, Dives_Akuru, Do- - gra, Duployan, Egyptian_Hieroglyphs, Elbasan, Elymaic, Ethiopic, Geor- + Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- + nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, + Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- + nian, Chakma, Cham, Cherokee, Chorasmian, Common, Coptic, Cuneiform, + Cypriot, Cypro_Minoan, Cyrillic, Deseret, Devanagari, Dives_Akuru, Do- + gra, Duployan, Egyptian_Hieroglyphs, Elbasan, Elymaic, Ethiopic, Geor- gian, Glagolitic, Gothic, Grantha, Greek, Gujarati, Gunjala_Gondi, Gur- mukhi, Han, Hangul, Hanifi_Rohingya, Hanunoo, Hatran, Hebrew, Hiragana, - Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- - tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, - Kharoshthi, Khitan_Small_Script, Khmer, Khojki, Khudawadi, Lao, Latin, - Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, - Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, Mede- + Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- + tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, + Kharoshthi, Khitan_Small_Script, Khmer, Khojki, Khudawadi, Lao, Latin, + Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Mahajani, + Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, Mede- faidrin, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, Meroitic_Hiero- glyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, Nabataean, Nandi- - nagari, New_Tai_Lue, Newa, Nko, Nushu, Nyakeng_Puachue_Hmong, Ogham, + nagari, New_Tai_Lue, Newa, Nko, Nushu, Nyakeng_Puachue_Hmong, Ogham, Ol_Chiki, Old_Hungarian, Old_Italic, Old_North_Arabian, Old_Permic, - Old_Persian, Old_Sogdian, Old_South_Arabian, Old_Turkic, Old_Uyghur, - Oriya, Osage, Osmanya, Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, + Old_Persian, Old_Sogdian, Old_South_Arabian, Old_Turkic, Old_Uyghur, + Oriya, Osage, Osmanya, Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician, Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Shavian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng, - Soyombo, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, + Soyombo, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Tangsa, Tangut, Telugu, Thaana, Thai, - Tibetan, Tifinagh, Tirhuta, Toto, Ugaritic, Unknown, Vai, Vithkuqi, + Tibetan, Tifinagh, Tirhuta, Toto, Ugaritic, Unknown, Vai, Vithkuqi, Wancho, Warang_Citi, Yezidi, Yi, Zanabazar_Square. Each character has exactly one Unicode general category property, spec- - ified by a two-letter abbreviation. For compatibility with Perl, nega- - tion can be specified by including a circumflex between the opening - brace and the property name. For example, \p{^Lu} is the same as + ified by a two-letter abbreviation. For compatibility with Perl, nega- + tion can be specified by including a circumflex between the opening + brace and the property name. For example, \p{^Lu} is the same as \P{Lu}. If only one letter is specified with \p or \P, it includes all the gen- - eral category properties that start with that letter. In this case, in - the absence of negation, the curly brackets in the escape sequence are + eral category properties that start with that letter. In this case, in + the absence of negation, the curly brackets in the escape sequence are optional; these two examples have the same effect: \p{L} @@ -7000,88 +7002,125 @@ BACKSLASH Zp Paragraph separator Zs Space separator - The special property L& is also supported: it matches a character that - has the Lu, Ll, or Lt property, in other words, a letter that is not - classified as a modifier or "other". + The special property LC, which has the synonym L&, is also supported: + it matches a character that has the Lu, Ll, or Lt property, in other + words, a letter that is not classified as a modifier or "other". - The Cs (Surrogate) property applies only to characters whose code - points are in the range U+D800 to U+DFFF. These characters are no dif- - ferent to any other character when PCRE2 is not in UTF mode (using the - 16-bit or 32-bit library). However, they are not valid in Unicode + The Cs (Surrogate) property applies only to characters whose code + points are in the range U+D800 to U+DFFF. These characters are no dif- + ferent to any other character when PCRE2 is not in UTF mode (using the + 16-bit or 32-bit library). However, they are not valid in Unicode strings and so cannot be tested by PCRE2 in UTF mode, unless UTF valid- - ity checking has been turned off (see the discussion of + ity checking has been turned off (see the discussion of PCRE2_NO_UTF_CHECK in the pcre2api page). - The long synonyms for property names that Perl supports (such as - \p{Letter}) are not supported by PCRE2, nor is it permitted to prefix + The long synonyms for property names that Perl supports (such as + \p{Letter}) are not supported by PCRE2, nor is it permitted to prefix any of these properties with "Is". No character that is in the Unicode table has the Cn (unassigned) prop- erty. Instead, this property is assumed for any code point that is not in the Unicode table. - Specifying caseless matching does not affect these escape sequences. - For example, \p{Lu} always matches only upper case letters. This is + Specifying caseless matching does not affect these escape sequences. + For example, \p{Lu} always matches only upper case letters. This is different from the behaviour of current versions of Perl. - Matching characters by Unicode property is not fast, because PCRE2 has - to do a multistage table lookup in order to find a character's prop- + Matching characters by Unicode property is not fast, because PCRE2 has + to do a multistage table lookup in order to find a character's prop- erty. That is why the traditional escape sequences such as \d and \w do - not use Unicode properties in PCRE2 by default, though you can make - them do so by setting the PCRE2_UCP option or by starting the pattern + not use Unicode properties in PCRE2 by default, though you can make + them do so by setting the PCRE2_UCP option or by starting the pattern with (*UCP). + Bi-directional properties for \p and \P + + Two properties relating to bi-directional text are supported: + + \p{Bidi_Control} matches a Bidi control character + \p{Bidi_Class:
} matches a character with the given class + + The recognized classes are: + + AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space + + For Bidi_Class, an equals sign may be used instead of a colon. The + class names are case-insensitive. As for other properties, only the + short names are recognized. + Extended grapheme clusters - The \X escape matches any number of Unicode characters that form an + The \X escape matches any number of Unicode characters that form an "extended grapheme cluster", and treats the sequence as an atomic group - (see below). Unicode supports various kinds of composite character by - giving each character a grapheme breaking property, and having rules + (see below). Unicode supports various kinds of composite character by + giving each character a grapheme breaking property, and having rules that use these properties to define the boundaries of extended grapheme - clusters. The rules are defined in Unicode Standard Annex 29, "Unicode - Text Segmentation". Unicode 11.0.0 abandoned the use of some previous - properties that had been used for emojis. Instead it introduced vari- - ous emoji-specific properties. PCRE2 uses only the Extended Picto- + clusters. The rules are defined in Unicode Standard Annex 29, "Unicode + Text Segmentation". Unicode 11.0.0 abandoned the use of some previous + properties that had been used for emojis. Instead it introduced vari- + ous emoji-specific properties. PCRE2 uses only the Extended Picto- graphic property. - \X always matches at least one character. Then it decides whether to + \X always matches at least one character. Then it decides whether to add additional characters according to the following rules for ending a cluster: 1. End at the end of the subject string. - 2. Do not end between CR and LF; otherwise end after any control char- + 2. Do not end between CR and LF; otherwise end after any control char- acter. - 3. Do not break Hangul (a Korean script) syllable sequences. Hangul - characters are of five types: L, V, T, LV, and LVT. An L character may - be followed by an L, V, LV, or LVT character; an LV or V character may - be followed by a V or T character; an LVT or T character may be fol- + 3. Do not break Hangul (a Korean script) syllable sequences. Hangul + characters are of five types: L, V, T, LV, and LVT. An L character may + be followed by an L, V, LV, or LVT character; an LV or V character may + be followed by a V or T character; an LVT or T character may be fol- lowed only by a T character. - 4. Do not end before extending characters or spacing marks or the - "zero-width joiner" character. Characters with the "mark" property al- + 4. Do not end before extending characters or spacing marks or the + "zero-width joiner" character. Characters with the "mark" property al- ways have the "extend" grapheme breaking property. 5. Do not end after prepend characters. 6. Do not break within emoji modifier sequences or emoji zwj sequences. That is, do not break between characters with the Extended_Pictographic - property. Extend and ZWJ characters are allowed between the charac- + property. Extend and ZWJ characters are allowed between the charac- ters. - 7. Do not break within emoji flag sequences. That is, do not break be- - tween regional indicator (RI) characters if there are an odd number of + 7. Do not break within emoji flag sequences. That is, do not break be- + tween regional indicator (RI) characters if there are an odd number of RI characters before the break point. 8. Otherwise, end the cluster. PCRE2's additional properties - As well as the standard Unicode properties described above, PCRE2 sup- + As well as the standard Unicode properties described above, PCRE2 sup- ports four more that make it possible to convert traditional escape se- - quences such as \w and \s to use Unicode properties. PCRE2 uses these - non-standard, non-Perl properties internally when PCRE2_UCP is set. + quences such as \w and \s to use Unicode properties. PCRE2 uses these + non-standard, non-Perl properties internally when PCRE2_UCP is set. However, they may also be used explicitly. These properties are: Xan Any alphanumeric character @@ -7089,72 +7128,72 @@ BACKSLASH Xsp Any Perl space character Xwd Any Perl "word" character - Xan matches characters that have either the L (letter) or the N (num- - ber) property. Xps matches the characters tab, linefeed, vertical tab, - form feed, or carriage return, and any other character that has the Z - (separator) property. Xsp is the same as Xps; in PCRE1 it used to ex- - clude vertical tab, for Perl compatibility, but Perl changed. Xwd + Xan matches characters that have either the L (letter) or the N (num- + ber) property. Xps matches the characters tab, linefeed, vertical tab, + form feed, or carriage return, and any other character that has the Z + (separator) property. Xsp is the same as Xps; in PCRE1 it used to ex- + clude vertical tab, for Perl compatibility, but Perl changed. Xwd matches the same characters as Xan, plus underscore. - There is another non-standard property, Xuc, which matches any charac- - ter that can be represented by a Universal Character Name in C++ and - other programming languages. These are the characters $, @, ` (grave - accent), and all characters with Unicode code points greater than or - equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that - most base (ASCII) characters are excluded. (Universal Character Names - are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit. + There is another non-standard property, Xuc, which matches any charac- + ter that can be represented by a Universal Character Name in C++ and + other programming languages. These are the characters $, @, ` (grave + accent), and all characters with Unicode code points greater than or + equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that + most base (ASCII) characters are excluded. (Universal Character Names + are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit. Note that the Xuc property does not match these sequences but the char- acters that they represent.) Resetting the match start - In normal use, the escape sequence \K causes any previously matched + In normal use, the escape sequence \K causes any previously matched characters not to be included in the final matched sequence that is re- turned. For example, the pattern: foo\Kbar - matches "foobar", but reports that it has matched "bar". \K does not + matches "foobar", but reports that it has matched "bar". \K does not interact with anchoring in any way. The pattern: ^foo\Kbar - matches only when the subject begins with "foobar" (in single line - mode), though it again reports the matched string as "bar". This fea- - ture is similar to a lookbehind assertion (described below). However, - in this case, the part of the subject before the real match does not - have to be of fixed length, as lookbehind assertions do. The use of \K - does not interfere with the setting of captured substrings. For exam- + matches only when the subject begins with "foobar" (in single line + mode), though it again reports the matched string as "bar". This fea- + ture is similar to a lookbehind assertion (described below). However, + in this case, the part of the subject before the real match does not + have to be of fixed length, as lookbehind assertions do. The use of \K + does not interfere with the setting of captured substrings. For exam- ple, when the pattern (foo)\Kbar matches "foobar", the first substring is still set to "foo". - From version 5.32.0 Perl forbids the use of \K in lookaround asser- - tions. From release 10.38 PCRE2 also forbids this by default. However, - the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option can be used when calling - pcre2_compile() to re-enable the previous behaviour. When this option + From version 5.32.0 Perl forbids the use of \K in lookaround asser- + tions. From release 10.38 PCRE2 also forbids this by default. However, + the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option can be used when calling + pcre2_compile() to re-enable the previous behaviour. When this option is set, \K is acted upon when it occurs inside positive assertions, but - is ignored in negative assertions. Note that when a pattern such as - (?=ab\K) matches, the reported start of the match can be greater than - the end of the match. Using \K in a lookbehind assertion at the start - of a pattern can also lead to odd effects. For example, consider this + is ignored in negative assertions. Note that when a pattern such as + (?=ab\K) matches, the reported start of the match can be greater than + the end of the match. Using \K in a lookbehind assertion at the start + of a pattern can also lead to odd effects. For example, consider this pattern: (?<=\Kfoo)bar - If the subject is "foobar", a call to pcre2_match() with a starting - offset of 3 succeeds and reports the matching string as "foobar", that - is, the start of the reported match is earlier than where the match + If the subject is "foobar", a call to pcre2_match() with a starting + offset of 3 succeeds and reports the matching string as "foobar", that + is, the start of the reported match is earlier than where the match started. Simple assertions - The final use of backslash is for certain simple assertions. An asser- - tion specifies a condition that has to be met at a particular point in - a match, without consuming any characters from the subject string. The - use of groups for more complicated assertions is described below. The + The final use of backslash is for certain simple assertions. An asser- + tion specifies a condition that has to be met at a particular point in + a match, without consuming any characters from the subject string. The + use of groups for more complicated assertions is described below. The backslashed assertions are: \b matches at a word boundary @@ -7165,193 +7204,193 @@ BACKSLASH \z matches only at the end of the subject \G matches at the first matching position in the subject - Inside a character class, \b has a different meaning; it matches the - backspace character. If any other of these assertions appears in a + Inside a character class, \b has a different meaning; it matches the + backspace character. If any other of these assertions appears in a character class, an "invalid escape sequence" error is generated. - A word boundary is a position in the subject string where the current - character and the previous character do not both match \w or \W (i.e. - one matches \w and the other matches \W), or the start or end of the - string if the first or last character matches \w, respectively. When - PCRE2 is built with Unicode support, the meanings of \w and \W can be + A word boundary is a position in the subject string where the current + character and the previous character do not both match \w or \W (i.e. + one matches \w and the other matches \W), or the start or end of the + string if the first or last character matches \w, respectively. When + PCRE2 is built with Unicode support, the meanings of \w and \W can be changed by setting the PCRE2_UCP option. When this is done, it also af- - fects \b and \B. Neither PCRE2 nor Perl has a separate "start of word" - or "end of word" metasequence. However, whatever follows \b normally - determines which it is. For example, the fragment \ba matches "a" at + fects \b and \B. Neither PCRE2 nor Perl has a separate "start of word" + or "end of word" metasequence. However, whatever follows \b normally + determines which it is. For example, the fragment \ba matches "a" at the start of a word. - The \A, \Z, and \z assertions differ from the traditional circumflex + The \A, \Z, and \z assertions differ from the traditional circumflex and dollar (described in the next section) in that they only ever match - at the very start and end of the subject string, whatever options are - set. Thus, they are independent of multiline mode. These three asser- - tions are not affected by the PCRE2_NOTBOL or PCRE2_NOTEOL options, - which affect only the behaviour of the circumflex and dollar metachar- - acters. However, if the startoffset argument of pcre2_match() is non- - zero, indicating that matching is to start at a point other than the - beginning of the subject, \A can never match. The difference between - \Z and \z is that \Z matches before a newline at the end of the string + at the very start and end of the subject string, whatever options are + set. Thus, they are independent of multiline mode. These three asser- + tions are not affected by the PCRE2_NOTBOL or PCRE2_NOTEOL options, + which affect only the behaviour of the circumflex and dollar metachar- + acters. However, if the startoffset argument of pcre2_match() is non- + zero, indicating that matching is to start at a point other than the + beginning of the subject, \A can never match. The difference between + \Z and \z is that \Z matches before a newline at the end of the string as well as at the very end, whereas \z matches only at the end. - The \G assertion is true only when the current matching position is at - the start point of the matching process, as specified by the startoff- - set argument of pcre2_match(). It differs from \A when the value of - startoffset is non-zero. By calling pcre2_match() multiple times with - appropriate arguments, you can mimic Perl's /g option, and it is in + The \G assertion is true only when the current matching position is at + the start point of the matching process, as specified by the startoff- + set argument of pcre2_match(). It differs from \A when the value of + startoffset is non-zero. By calling pcre2_match() multiple times with + appropriate arguments, you can mimic Perl's /g option, and it is in this kind of implementation where \G can be useful. - Note, however, that PCRE2's implementation of \G, being true at the - starting character of the matching process, is subtly different from - Perl's, which defines it as true at the end of the previous match. In - Perl, these can be different when the previously matched string was + Note, however, that PCRE2's implementation of \G, being true at the + starting character of the matching process, is subtly different from + Perl's, which defines it as true at the end of the previous match. In + Perl, these can be different when the previously matched string was empty. Because PCRE2 does just one match at a time, it cannot reproduce this behaviour. - If all the alternatives of a pattern begin with \G, the expression is + If all the alternatives of a pattern begin with \G, the expression is anchored to the starting match position, and the "anchored" flag is set in the compiled regular expression. CIRCUMFLEX AND DOLLAR - The circumflex and dollar metacharacters are zero-width assertions. - That is, they test for a particular condition being true without con- + The circumflex and dollar metacharacters are zero-width assertions. + That is, they test for a particular condition being true without con- suming any characters from the subject string. These two metacharacters - are concerned with matching the starts and ends of lines. If the new- - line convention is set so that only the two-character sequence CRLF is - recognized as a newline, isolated CR and LF characters are treated as + are concerned with matching the starts and ends of lines. If the new- + line convention is set so that only the two-character sequence CRLF is + recognized as a newline, isolated CR and LF characters are treated as ordinary data characters, and are not recognized as newlines. Outside a character class, in the default matching mode, the circumflex - character is an assertion that is true only if the current matching - point is at the start of the subject string. If the startoffset argu- - ment of pcre2_match() is non-zero, or if PCRE2_NOTBOL is set, circum- - flex can never match if the PCRE2_MULTILINE option is unset. Inside a - character class, circumflex has an entirely different meaning (see be- + character is an assertion that is true only if the current matching + point is at the start of the subject string. If the startoffset argu- + ment of pcre2_match() is non-zero, or if PCRE2_NOTBOL is set, circum- + flex can never match if the PCRE2_MULTILINE option is unset. Inside a + character class, circumflex has an entirely different meaning (see be- low). - Circumflex need not be the first character of the pattern if a number - of alternatives are involved, but it should be the first thing in each - alternative in which it appears if the pattern is ever to match that - branch. If all possible alternatives start with a circumflex, that is, - if the pattern is constrained to match only at the start of the sub- - ject, it is said to be an "anchored" pattern. (There are also other + Circumflex need not be the first character of the pattern if a number + of alternatives are involved, but it should be the first thing in each + alternative in which it appears if the pattern is ever to match that + branch. If all possible alternatives start with a circumflex, that is, + if the pattern is constrained to match only at the start of the sub- + ject, it is said to be an "anchored" pattern. (There are also other constructs that can cause a pattern to be anchored.) - The dollar character is an assertion that is true only if the current - matching point is at the end of the subject string, or immediately be- - fore a newline at the end of the string (by default), unless PCRE2_NO- - TEOL is set. Note, however, that it does not actually match the new- - line. Dollar need not be the last character of the pattern if a number - of alternatives are involved, but it should be the last item in any - branch in which it appears. Dollar has no special meaning in a charac- + The dollar character is an assertion that is true only if the current + matching point is at the end of the subject string, or immediately be- + fore a newline at the end of the string (by default), unless PCRE2_NO- + TEOL is set. Note, however, that it does not actually match the new- + line. Dollar need not be the last character of the pattern if a number + of alternatives are involved, but it should be the last item in any + branch in which it appears. Dollar has no special meaning in a charac- ter class. - The meaning of dollar can be changed so that it matches only at the - very end of the string, by setting the PCRE2_DOLLAR_ENDONLY option at + The meaning of dollar can be changed so that it matches only at the + very end of the string, by setting the PCRE2_DOLLAR_ENDONLY option at compile time. This does not affect the \Z assertion. The meanings of the circumflex and dollar metacharacters are changed if - the PCRE2_MULTILINE option is set. When this is the case, a dollar - character matches before any newlines in the string, as well as at the - very end, and a circumflex matches immediately after internal newlines - as well as at the start of the subject string. It does not match after - a newline that ends the string, for compatibility with Perl. However, + the PCRE2_MULTILINE option is set. When this is the case, a dollar + character matches before any newlines in the string, as well as at the + very end, and a circumflex matches immediately after internal newlines + as well as at the start of the subject string. It does not match after + a newline that ends the string, for compatibility with Perl. However, this can be changed by setting the PCRE2_ALT_CIRCUMFLEX option. - For example, the pattern /^abc$/ matches the subject string "def\nabc" - (where \n represents a newline) in multiline mode, but not otherwise. - Consequently, patterns that are anchored in single line mode because - all branches start with ^ are not anchored in multiline mode, and a - match for circumflex is possible when the startoffset argument of - pcre2_match() is non-zero. The PCRE2_DOLLAR_ENDONLY option is ignored + For example, the pattern /^abc$/ matches the subject string "def\nabc" + (where \n represents a newline) in multiline mode, but not otherwise. + Consequently, patterns that are anchored in single line mode because + all branches start with ^ are not anchored in multiline mode, and a + match for circumflex is possible when the startoffset argument of + pcre2_match() is non-zero. The PCRE2_DOLLAR_ENDONLY option is ignored if PCRE2_MULTILINE is set. - When the newline convention (see "Newline conventions" below) recog- - nizes the two-character sequence CRLF as a newline, this is preferred, - even if the single characters CR and LF are also recognized as new- - lines. For example, if the newline convention is "any", a multiline - mode circumflex matches before "xyz" in the string "abc\r\nxyz" rather - than after CR, even though CR on its own is a valid newline. (It also + When the newline convention (see "Newline conventions" below) recog- + nizes the two-character sequence CRLF as a newline, this is preferred, + even if the single characters CR and LF are also recognized as new- + lines. For example, if the newline convention is "any", a multiline + mode circumflex matches before "xyz" in the string "abc\r\nxyz" rather + than after CR, even though CR on its own is a valid newline. (It also matches at the very start of the string, of course.) - Note that the sequences \A, \Z, and \z can be used to match the start - and end of the subject in both modes, and if all branches of a pattern - start with \A it is always anchored, whether or not PCRE2_MULTILINE is + Note that the sequences \A, \Z, and \z can be used to match the start + and end of the subject in both modes, and if all branches of a pattern + start with \A it is always anchored, whether or not PCRE2_MULTILINE is set. FULL STOP (PERIOD, DOT) AND \N Outside a character class, a dot in the pattern matches any one charac- - ter in the subject string except (by default) a character that signi- + ter in the subject string except (by default) a character that signi- fies the end of a line. One or more characters may be specified as line terminators (see "Newline conventions" above). - Dot never matches a single line-ending character. When the two-charac- - ter sequence CRLF is the only line ending, dot does not match CR if it - is immediately followed by LF, but otherwise it matches all characters - (including isolated CRs and LFs). When ANYCRLF is selected for line - endings, no occurences of CR of LF match dot. When all Unicode line + Dot never matches a single line-ending character. When the two-charac- + ter sequence CRLF is the only line ending, dot does not match CR if it + is immediately followed by LF, but otherwise it matches all characters + (including isolated CRs and LFs). When ANYCRLF is selected for line + endings, no occurences of CR of LF match dot. When all Unicode line endings are being recognized, dot does not match CR or LF or any of the other line ending characters. - The behaviour of dot with regard to newlines can be changed. If the - PCRE2_DOTALL option is set, a dot matches any one character, without - exception. If the two-character sequence CRLF is present in the sub- + The behaviour of dot with regard to newlines can be changed. If the + PCRE2_DOTALL option is set, a dot matches any one character, without + exception. If the two-character sequence CRLF is present in the sub- ject string, it takes two dots to match it. - The handling of dot is entirely independent of the handling of circum- - flex and dollar, the only relationship being that they both involve + The handling of dot is entirely independent of the handling of circum- + flex and dollar, the only relationship being that they both involve newlines. Dot has no special meaning in a character class. - The escape sequence \N when not followed by an opening brace behaves - like a dot, except that it is not affected by the PCRE2_DOTALL option. - In other words, it matches any character except one that signifies the + The escape sequence \N when not followed by an opening brace behaves + like a dot, except that it is not affected by the PCRE2_DOTALL option. + In other words, it matches any character except one that signifies the end of a line. When \N is followed by an opening brace it has a different meaning. See - the section entitled "Non-printing characters" above for details. Perl - also uses \N{name} to specify characters by Unicode name; PCRE2 does + the section entitled "Non-printing characters" above for details. Perl + also uses \N{name} to specify characters by Unicode name; PCRE2 does not support this. MATCHING A SINGLE CODE UNIT - Outside a character class, the escape sequence \C matches any one code - unit, whether or not a UTF mode is set. In the 8-bit library, one code - unit is one byte; in the 16-bit library it is a 16-bit unit; in the - 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches - line-ending characters. The feature is provided in Perl in order to + Outside a character class, the escape sequence \C matches any one code + unit, whether or not a UTF mode is set. In the 8-bit library, one code + unit is one byte; in the 16-bit library it is a 16-bit unit; in the + 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches + line-ending characters. The feature is provided in Perl in order to match individual bytes in UTF-8 mode, but it is unclear how it can use- fully be used. - Because \C breaks up characters into individual code units, matching - one unit with \C in UTF-8 or UTF-16 mode means that the rest of the + Because \C breaks up characters into individual code units, matching + one unit with \C in UTF-8 or UTF-16 mode means that the rest of the string may start with a malformed UTF character. This has undefined re- sults, because PCRE2 assumes that it is matching character by character in a valid UTF string (by default it checks the subject string's valid- - ity at the start of processing unless the PCRE2_NO_UTF_CHECK or + ity at the start of processing unless the PCRE2_NO_UTF_CHECK or PCRE2_MATCH_INVALID_UTF option is used). - An application can lock out the use of \C by setting the - PCRE2_NEVER_BACKSLASH_C option when compiling a pattern. It is also + An application can lock out the use of \C by setting the + PCRE2_NEVER_BACKSLASH_C option when compiling a pattern. It is also possible to build PCRE2 with the use of \C permanently disabled. - PCRE2 does not allow \C to appear in lookbehind assertions (described - below) in UTF-8 or UTF-16 modes, because this would make it impossible - to calculate the length of the lookbehind. Neither the alternative + PCRE2 does not allow \C to appear in lookbehind assertions (described + below) in UTF-8 or UTF-16 modes, because this would make it impossible + to calculate the length of the lookbehind. Neither the alternative matching function pcre2_dfa_match() nor the JIT optimizer support \C in these UTF modes. The former gives a match-time error; the latter fails to optimize and so the match is always run using the interpreter. - In the 32-bit library, however, \C is always supported (when not ex- - plicitly locked out) because it always matches a single code unit, + In the 32-bit library, however, \C is always supported (when not ex- + plicitly locked out) because it always matches a single code unit, whether or not UTF-32 is specified. In general, the \C escape sequence is best avoided. However, one way of - using it that avoids the problem of malformed UTF-8 or UTF-16 charac- - ters is to use a lookahead to check the length of the next character, - as in this pattern, which could be used with a UTF-8 string (ignore + using it that avoids the problem of malformed UTF-8 or UTF-16 charac- + ters is to use a lookahead to check the length of the next character, + as in this pattern, which could be used with a UTF-8 string (ignore white space and line breaks): (?| (?=[\x00-\x7f])(\C) | @@ -7359,11 +7398,11 @@ MATCHING A SINGLE CODE UNIT (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) - In this example, a group that starts with (?| resets the capturing - parentheses numbers in each alternative (see "Duplicate Group Numbers" + In this example, a group that starts with (?| resets the capturing + parentheses numbers in each alternative (see "Duplicate Group Numbers" below). The assertions at the start of each branch check the next UTF-8 - character for values whose encoding uses 1, 2, 3, or 4 bytes, respec- - tively. The character's individual bytes are then captured by the ap- + character for values whose encoding uses 1, 2, 3, or 4 bytes, respec- + tively. The character's individual bytes are then captured by the ap- propriate number of \C groups. @@ -7371,125 +7410,125 @@ SQUARE BRACKETS AND CHARACTER CLASSES An opening square bracket introduces a character class, terminated by a closing square bracket. A closing square bracket on its own is not spe- - cial by default. If a closing square bracket is required as a member + cial by default. If a closing square bracket is required as a member of the class, it should be the first data character in the class (after - an initial circumflex, if present) or escaped with a backslash. This - means that, by default, an empty class cannot be defined. However, if - the PCRE2_ALLOW_EMPTY_CLASS option is set, a closing square bracket at + an initial circumflex, if present) or escaped with a backslash. This + means that, by default, an empty class cannot be defined. However, if + the PCRE2_ALLOW_EMPTY_CLASS option is set, a closing square bracket at the start does end the (empty) class. - A character class matches a single character in the subject. A matched + A character class matches a single character in the subject. A matched character must be in the set of characters defined by the class, unless - the first character in the class definition is a circumflex, in which + the first character in the class definition is a circumflex, in which case the subject character must not be in the set defined by the class. - If a circumflex is actually required as a member of the class, ensure + If a circumflex is actually required as a member of the class, ensure it is not the first character, or escape it with a backslash. - For example, the character class [aeiou] matches any lower case vowel, - while [^aeiou] matches any character that is not a lower case vowel. + For example, the character class [aeiou] matches any lower case vowel, + while [^aeiou] matches any character that is not a lower case vowel. Note that a circumflex is just a convenient notation for specifying the - characters that are in the class by enumerating those that are not. A - class that starts with a circumflex is not an assertion; it still con- - sumes a character from the subject string, and therefore it fails if + characters that are in the class by enumerating those that are not. A + class that starts with a circumflex is not an assertion; it still con- + sumes a character from the subject string, and therefore it fails if the current pointer is at the end of the string. - Characters in a class may be specified by their code points using \o, - \x, or \N{U+hh..} in the usual way. When caseless matching is set, any - letters in a class represent both their upper case and lower case ver- - sions, so for example, a caseless [aeiou] matches "A" as well as "a", - and a caseless [^aeiou] does not match "A", whereas a caseful version - would. Note that there are two ASCII characters, K and S, that, in ad- - dition to their lower case ASCII equivalents, are case-equivalent with - Unicode U+212A (Kelvin sign) and U+017F (long S) respectively when ei- + Characters in a class may be specified by their code points using \o, + \x, or \N{U+hh..} in the usual way. When caseless matching is set, any + letters in a class represent both their upper case and lower case ver- + sions, so for example, a caseless [aeiou] matches "A" as well as "a", + and a caseless [^aeiou] does not match "A", whereas a caseful version + would. Note that there are two ASCII characters, K and S, that, in ad- + dition to their lower case ASCII equivalents, are case-equivalent with + Unicode U+212A (Kelvin sign) and U+017F (long S) respectively when ei- ther PCRE2_UTF or PCRE2_UCP is set. - Characters that might indicate line breaks are never treated in any - special way when matching character classes, whatever line-ending se- - quence is in use, and whatever setting of the PCRE2_DOTALL and - PCRE2_MULTILINE options is used. A class such as [^a] always matches + Characters that might indicate line breaks are never treated in any + special way when matching character classes, whatever line-ending se- + quence is in use, and whatever setting of the PCRE2_DOTALL and + PCRE2_MULTILINE options is used. A class such as [^a] always matches one of these characters. The generic character type escape sequences \d, \D, \h, \H, \p, \P, \s, - \S, \v, \V, \w, and \W may appear in a character class, and add the - characters that they match to the class. For example, [\dABCDEF] - matches any hexadecimal digit. In UTF modes, the PCRE2_UCP option af- + \S, \v, \V, \w, and \W may appear in a character class, and add the + characters that they match to the class. For example, [\dABCDEF] + matches any hexadecimal digit. In UTF modes, the PCRE2_UCP option af- fects the meanings of \d, \s, \w and their upper case partners, just as it does when they appear outside a character class, as described in the - section entitled "Generic character types" above. The escape sequence - \b has a different meaning inside a character class; it matches the - backspace character. The sequences \B, \R, and \X are not special in- - side a character class. Like any other unrecognized escape sequences, - they cause an error. The same is true for \N when not followed by an + section entitled "Generic character types" above. The escape sequence + \b has a different meaning inside a character class; it matches the + backspace character. The sequences \B, \R, and \X are not special in- + side a character class. Like any other unrecognized escape sequences, + they cause an error. The same is true for \N when not followed by an opening brace. - The minus (hyphen) character can be used to specify a range of charac- - ters in a character class. For example, [d-m] matches any letter be- - tween d and m, inclusive. If a minus character is required in a class, - it must be escaped with a backslash or appear in a position where it - cannot be interpreted as indicating a range, typically as the first or + The minus (hyphen) character can be used to specify a range of charac- + ters in a character class. For example, [d-m] matches any letter be- + tween d and m, inclusive. If a minus character is required in a class, + it must be escaped with a backslash or appear in a position where it + cannot be interpreted as indicating a range, typically as the first or last character in the class, or immediately after a range. For example, [b-d-z] matches letters in the range b to d, a hyphen character, or z. Perl treats a hyphen as a literal if it appears before or after a POSIX class (see below) or before or after a character type escape such as as - \d or \H. However, unless the hyphen is the last character in the - class, Perl outputs a warning in its warning mode, as this is most - likely a user error. As PCRE2 has no facility for warning, an error is + \d or \H. However, unless the hyphen is the last character in the + class, Perl outputs a warning in its warning mode, as this is most + likely a user error. As PCRE2 has no facility for warning, an error is given in these cases. It is not possible to have the literal character "]" as the end charac- - ter of a range. A pattern such as [W-]46] is interpreted as a class of - two characters ("W" and "-") followed by a literal string "46]", so it - would match "W46]" or "-46]". However, if the "]" is escaped with a - backslash it is interpreted as the end of range, so [W-\]46] is inter- - preted as a class containing a range followed by two other characters. - The octal or hexadecimal representation of "]" can also be used to end + ter of a range. A pattern such as [W-]46] is interpreted as a class of + two characters ("W" and "-") followed by a literal string "46]", so it + would match "W46]" or "-46]". However, if the "]" is escaped with a + backslash it is interpreted as the end of range, so [W-\]46] is inter- + preted as a class containing a range followed by two other characters. + The octal or hexadecimal representation of "]" can also be used to end a range. Ranges normally include all code points between the start and end char- - acters, inclusive. They can also be used for code points specified nu- - merically, for example [\000-\037]. Ranges can include any characters - that are valid for the current mode. In any UTF mode, the so-called - "surrogate" characters (those whose code points lie between 0xd800 and - 0xdfff inclusive) may not be specified explicitly by default (the - PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES option disables this check). How- + acters, inclusive. They can also be used for code points specified nu- + merically, for example [\000-\037]. Ranges can include any characters + that are valid for the current mode. In any UTF mode, the so-called + "surrogate" characters (those whose code points lie between 0xd800 and + 0xdfff inclusive) may not be specified explicitly by default (the + PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES option disables this check). How- ever, ranges such as [\x{d7ff}-\x{e000}], which include the surrogates, are always permitted. - There is a special case in EBCDIC environments for ranges whose end + There is a special case in EBCDIC environments for ranges whose end points are both specified as literal letters in the same case. For com- - patibility with Perl, EBCDIC code points within the range that are not - letters are omitted. For example, [h-k] matches only four characters, + patibility with Perl, EBCDIC code points within the range that are not + letters are omitted. For example, [h-k] matches only four characters, even though the codes for h and k are 0x88 and 0x92, a range of 11 code - points. However, if the range is specified numerically, for example, + points. However, if the range is specified numerically, for example, [\x88-\x92] or [h-\x92], all code points are included. If a range that includes letters is used when caseless matching is set, it matches the letters in either case. For example, [W-c] is equivalent - to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if - character tables for a French locale are in use, [\xc8-\xcb] matches + to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if + character tables for a French locale are in use, [\xc8-\xcb] matches accented E characters in both cases. - A circumflex can conveniently be used with the upper case character - types to specify a more restricted set of characters than the matching - lower case type. For example, the class [^\W_] matches any letter or + A circumflex can conveniently be used with the upper case character + types to specify a more restricted set of characters than the matching + lower case type. For example, the class [^\W_] matches any letter or digit, but not underscore, whereas [\w] includes underscore. A positive character class should be read as "something OR something OR ..." and a negative class as "NOT something AND NOT something AND NOT ...". - The only metacharacters that are recognized in character classes are - backslash, hyphen (only where it can be interpreted as specifying a - range), circumflex (only at the start), opening square bracket (only - when it can be interpreted as introducing a POSIX class name, or for a - special compatibility feature - see the next two sections), and the - terminating closing square bracket. However, escaping other non-al- + The only metacharacters that are recognized in character classes are + backslash, hyphen (only where it can be interpreted as specifying a + range), circumflex (only at the start), opening square bracket (only + when it can be interpreted as introducing a POSIX class name, or for a + special compatibility feature - see the next two sections), and the + terminating closing square bracket. However, escaping other non-al- phanumeric characters does no harm. POSIX CHARACTER CLASSES Perl supports the POSIX notation for character classes. This uses names - enclosed by [: and :] within the enclosing square brackets. PCRE2 also + enclosed by [: and :] within the enclosing square brackets. PCRE2 also supports this notation. For example, [01[:alpha:]%] @@ -7512,13 +7551,13 @@ POSIX CHARACTER CLASSES word "word" characters (same as \w) xdigit hexadecimal digits - The default "space" characters are HT (9), LF (10), VT (11), FF (12), - CR (13), and space (32). If locale-specific matching is taking place, - the list of space characters may be different; there may be fewer or + The default "space" characters are HT (9), LF (10), VT (11), FF (12), + CR (13), and space (32). If locale-specific matching is taking place, + the list of space characters may be different; there may be fewer or more of them. "Space" and \s match the same set of characters. - The name "word" is a Perl extension, and "blank" is a GNU extension - from Perl 5.8. Another Perl extension is negation, which is indicated + The name "word" is a Perl extension, and "blank" is a GNU extension + from Perl 5.8. Another Perl extension is negation, which is indicated by a ^ character after the colon. For example, [12[:^digit:]] @@ -7529,10 +7568,10 @@ POSIX CHARACTER CLASSES By default, characters with values greater than 127 do not match any of the POSIX character classes, although this may be different for charac- - ters in the range 128-255 when locale-specific matching is happening. - However, if the PCRE2_UCP option is passed to pcre2_compile(), some of - the classes are changed so that Unicode character properties are used. - This is achieved by replacing certain POSIX classes with other se- + ters in the range 128-255 when locale-specific matching is happening. + However, if the PCRE2_UCP option is passed to pcre2_compile(), some of + the classes are changed so that Unicode character properties are used. + This is achieved by replacing certain POSIX classes with other se- quences, as follows: [:alnum:] becomes \p{Xan} @@ -7545,10 +7584,10 @@ POSIX CHARACTER CLASSES [:upper:] becomes \p{Lu} [:word:] becomes \p{Xwd} - Negated versions, such as [:^alpha:] use \P instead of \p. Three other + Negated versions, such as [:^alpha:] use \P instead of \p. Three other POSIX classes are handled specially in UCP mode: - [:graph:] This matches characters that have glyphs that mark the page + [:graph:] This matches characters that have glyphs that mark the page when printed. In Unicode property terms, it matches all char- acters with the L, M, N, P, S, or Cf properties, except for: @@ -7557,60 +7596,60 @@ POSIX CHARACTER CLASSES U+2066 - U+2069 Various "isolate"s - [:print:] This matches the same characters as [:graph:] plus space - characters that are not controls, that is, characters with + [:print:] This matches the same characters as [:graph:] plus space + characters that are not controls, that is, characters with the Zs property. [:punct:] This matches all characters that have the Unicode P (punctua- - tion) property, plus those characters with code points less + tion) property, plus those characters with code points less than 256 that have the S (Symbol) property. - The other POSIX classes are unchanged, and match only characters with + The other POSIX classes are unchanged, and match only characters with code points less than 256. COMPATIBILITY FEATURE FOR WORD BOUNDARIES - In the POSIX.2 compliant library that was included in 4.4BSD Unix, the - ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" + In the POSIX.2 compliant library that was included in 4.4BSD Unix, the + ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" and "end of word". PCRE2 treats these items as follows: [[:<:]] is converted to \b(?=\w) [[:>:]] is converted to \b(?<=\w) Only these exact character sequences are recognized. A sequence such as - [a[:<:]b] provokes error for an unrecognized POSIX class name. This - support is not compatible with Perl. It is provided to help migrations + [a[:<:]b] provokes error for an unrecognized POSIX class name. This + support is not compatible with Perl. It is provided to help migrations from other environments, and is best not used in any new patterns. Note - that \b matches at the start and the end of a word (see "Simple asser- - tions" above), and in a Perl-style pattern the preceding or following - character normally shows which is wanted, without the need for the as- - sertions that are used above in order to give exactly the POSIX behav- + that \b matches at the start and the end of a word (see "Simple asser- + tions" above), and in a Perl-style pattern the preceding or following + character normally shows which is wanted, without the need for the as- + sertions that are used above in order to give exactly the POSIX behav- iour. VERTICAL BAR - Vertical bar characters are used to separate alternative patterns. For + Vertical bar characters are used to separate alternative patterns. For example, the pattern gilbert|sullivan - matches either "gilbert" or "sullivan". Any number of alternatives may - appear, and an empty alternative is permitted (matching the empty + matches either "gilbert" or "sullivan". Any number of alternatives may + appear, and an empty alternative is permitted (matching the empty string). The matching process tries each alternative in turn, from left - to right, and the first one that succeeds is used. If the alternatives - are within a group (defined below), "succeeds" means matching the rest + to right, and the first one that succeeds is used. If the alternatives + are within a group (defined below), "succeeds" means matching the rest of the main pattern as well as the alternative in the group. INTERNAL OPTION SETTING - The settings of the PCRE2_CASELESS, PCRE2_MULTILINE, PCRE2_DOTALL, - PCRE2_EXTENDED, PCRE2_EXTENDED_MORE, and PCRE2_NO_AUTO_CAPTURE options - can be changed from within the pattern by a sequence of letters en- - closed between "(?" and ")". These options are Perl-compatible, and - are described in detail in the pcre2api documentation. The option let- + The settings of the PCRE2_CASELESS, PCRE2_MULTILINE, PCRE2_DOTALL, + PCRE2_EXTENDED, PCRE2_EXTENDED_MORE, and PCRE2_NO_AUTO_CAPTURE options + can be changed from within the pattern by a sequence of letters en- + closed between "(?" and ")". These options are Perl-compatible, and + are described in detail in the pcre2api documentation. The option let- ters are: i for PCRE2_CASELESS @@ -7622,48 +7661,48 @@ INTERNAL OPTION SETTING For example, (?im) sets caseless, multiline matching. It is also possi- ble to unset these options by preceding the relevant letters with a hy- - phen, for example (?-im). The two "extended" options are not indepen- + phen, for example (?-im). The two "extended" options are not indepen- dent; unsetting either one cancels the effects of both of them. - A combined setting and unsetting such as (?im-sx), which sets - PCRE2_CASELESS and PCRE2_MULTILINE while unsetting PCRE2_DOTALL and - PCRE2_EXTENDED, is also permitted. Only one hyphen may appear in the - options string. If a letter appears both before and after the hyphen, - the option is unset. An empty options setting "(?)" is allowed. Need- + A combined setting and unsetting such as (?im-sx), which sets + PCRE2_CASELESS and PCRE2_MULTILINE while unsetting PCRE2_DOTALL and + PCRE2_EXTENDED, is also permitted. Only one hyphen may appear in the + options string. If a letter appears both before and after the hyphen, + the option is unset. An empty options setting "(?)" is allowed. Need- less to say, it has no effect. - If the first character following (? is a circumflex, it causes all of - the above options to be unset. Thus, (?^) is equivalent to (?-imnsx). - Letters may follow the circumflex to cause some options to be re-in- + If the first character following (? is a circumflex, it causes all of + the above options to be unset. Thus, (?^) is equivalent to (?-imnsx). + Letters may follow the circumflex to cause some options to be re-in- stated, but a hyphen may not appear. - The PCRE2-specific options PCRE2_DUPNAMES and PCRE2_UNGREEDY can be - changed in the same way as the Perl-compatible options by using the + The PCRE2-specific options PCRE2_DUPNAMES and PCRE2_UNGREEDY can be + changed in the same way as the Perl-compatible options by using the characters J and U respectively. However, these are not unset by (?^). - When one of these option changes occurs at top level (that is, not in- - side group parentheses), the change applies to the remainder of the - pattern that follows. An option change within a group (see below for a + When one of these option changes occurs at top level (that is, not in- + side group parentheses), the change applies to the remainder of the + pattern that follows. An option change within a group (see below for a description of groups) affects only that part of the group that follows it, so (a(?i)b)c - matches abc and aBc and no other strings (assuming PCRE2_CASELESS is - not used). By this means, options can be made to have different set- + matches abc and aBc and no other strings (assuming PCRE2_CASELESS is + not used). By this means, options can be made to have different set- tings in different parts of the pattern. Any changes made in one alter- - native do carry on into subsequent branches within the same group. For + native do carry on into subsequent branches within the same group. For example, (a(?i)b|c) - matches "ab", "aB", "c", and "C", even though when matching "C" the - first branch is abandoned before the option setting. This is because - the effects of option settings happen at compile time. There would be + matches "ab", "aB", "c", and "C", even though when matching "C" the + first branch is abandoned before the option setting. This is because + the effects of option settings happen at compile time. There would be some very weird behaviour otherwise. - As a convenient shorthand, if any option settings are required at the - start of a non-capturing group (see the next section), the option let- + As a convenient shorthand, if any option settings are required at the + start of a non-capturing group (see the next section), the option let- ters may appear between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) @@ -7671,39 +7710,39 @@ INTERNAL OPTION SETTING match exactly the same set of strings. - Note: There are other PCRE2-specific options, applying to the whole - pattern, which can be set by the application when the compiling func- - tion is called. In addition, the pattern can contain special leading - sequences such as (*CRLF) to override what the application has set or - what has been defaulted. Details are given in the section entitled + Note: There are other PCRE2-specific options, applying to the whole + pattern, which can be set by the application when the compiling func- + tion is called. In addition, the pattern can contain special leading + sequences such as (*CRLF) to override what the application has set or + what has been defaulted. Details are given in the section entitled "Newline sequences" above. There are also the (*UTF) and (*UCP) leading - sequences that can be used to set UTF and Unicode property modes; they - are equivalent to setting the PCRE2_UTF and PCRE2_UCP options, respec- - tively. However, the application can set the PCRE2_NEVER_UTF and - PCRE2_NEVER_UCP options, which lock out the use of the (*UTF) and + sequences that can be used to set UTF and Unicode property modes; they + are equivalent to setting the PCRE2_UTF and PCRE2_UCP options, respec- + tively. However, the application can set the PCRE2_NEVER_UTF and + PCRE2_NEVER_UCP options, which lock out the use of the (*UTF) and (*UCP) sequences. GROUPS - Groups are delimited by parentheses (round brackets), which can be + Groups are delimited by parentheses (round brackets), which can be nested. Turning part of a pattern into a group does two things: 1. It localizes a set of alternatives. For example, the pattern cat(aract|erpillar|) - matches "cataract", "caterpillar", or "cat". Without the parentheses, + matches "cataract", "caterpillar", or "cat". Without the parentheses, it would match "cataract", "erpillar" or an empty string. - 2. It creates a "capture group". This means that, when the whole pat- - tern matches, the portion of the subject string that matched the group - is passed back to the caller, separately from the portion that matched - the whole pattern. (This applies only to the traditional matching + 2. It creates a "capture group". This means that, when the whole pat- + tern matches, the portion of the subject string that matched the group + is passed back to the caller, separately from the portion that matched + the whole pattern. (This applies only to the traditional matching function; the DFA matching function does not support capturing.) Opening parentheses are counted from left to right (starting from 1) to - obtain numbers for capture groups. For example, if the string "the red + obtain numbers for capture groups. For example, if the string "the red king" is matched against the pattern the ((red|white) (king|queen)) @@ -7711,11 +7750,11 @@ GROUPS the captured substrings are "red king", "red", and "king", and are num- bered 1, 2, and 3, respectively. - The fact that plain parentheses fulfil two functions is not always - helpful. There are often times when grouping is required without cap- - turing. If an opening parenthesis is followed by a question mark and a - colon, the group does not do any capturing, and is not counted when - computing the number of any subsequent capture groups. For example, if + The fact that plain parentheses fulfil two functions is not always + helpful. There are often times when grouping is required without cap- + turing. If an opening parenthesis is followed by a question mark and a + colon, the group does not do any capturing, and is not counted when + computing the number of any subsequent capture groups. For example, if the string "the white queen" is matched against the pattern the ((?:red|white) (king|queen)) @@ -7723,16 +7762,16 @@ GROUPS the captured substrings are "white queen" and "queen", and are numbered 1 and 2. The maximum number of capture groups is 65535. - As a convenient shorthand, if any option settings are required at the - start of a non-capturing group, the option letters may appear between + As a convenient shorthand, if any option settings are required at the + start of a non-capturing group, the option letters may appear between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) (?:(?i)saturday|sunday) match exactly the same set of strings. Because alternative branches are - tried from left to right, and options are not reset until the end of - the group is reached, an option setting in one branch does affect sub- + tried from left to right, and options are not reset until the end of + the group is reached, an option setting in one branch does affect sub- sequent branches, so the above patterns match "SUNDAY" as well as "Sat- urday". @@ -7740,19 +7779,19 @@ GROUPS DUPLICATE GROUP NUMBERS Perl 5.10 introduced a feature whereby each alternative in a group uses - the same numbers for its capturing parentheses. Such a group starts - with (?| and is itself a non-capturing group. For example, consider + the same numbers for its capturing parentheses. Such a group starts + with (?| and is itself a non-capturing group. For example, consider this pattern: (?|(Sat)ur|(Sun))day - Because the two alternatives are inside a (?| group, both sets of cap- - turing parentheses are numbered one. Thus, when the pattern matches, - you can look at captured substring number one, whichever alternative - matched. This construct is useful when you want to capture part, but + Because the two alternatives are inside a (?| group, both sets of cap- + turing parentheses are numbered one. Thus, when the pattern matches, + you can look at captured substring number one, whichever alternative + matched. This construct is useful when you want to capture part, but not all, of one of a number of alternatives. Inside a (?| group, paren- - theses are numbered as usual, but the number is reset at the start of - each branch. The numbers of any capturing parentheses that follow the + theses are numbered as usual, but the number is reset at the start of + each branch. The numbers of any capturing parentheses that follow the whole group start after the highest number used in any branch. The fol- lowing example is taken from the Perl documentation. The numbers under- neath show in which buffer the captured content will be stored. @@ -7761,13 +7800,13 @@ DUPLICATE GROUP NUMBERS / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x # 1 2 2 3 2 3 4 - A backreference to a capture group uses the most recent value that is + A backreference to a capture group uses the most recent value that is set for the group. The following pattern matches "abcabc" or "defdef": /(?|(abc)|(def))\1/ - In contrast, a subroutine call to a capture group always refers to the - first one in the pattern with the given number. The following pattern + In contrast, a subroutine call to a capture group always refers to the + first one in the pattern with the given number. The following pattern matches "abcabc" or "defabc": /(?|(abc)|(def))(?1)/ @@ -7778,24 +7817,24 @@ DUPLICATE GROUP NUMBERS If a condition test for a group's having matched refers to a non-unique number, the test is true if any group with that number has matched. - An alternative approach to using this "branch reset" feature is to use + An alternative approach to using this "branch reset" feature is to use duplicate named groups, as described in the next section. NAMED CAPTURE GROUPS Identifying capture groups by number is simple, but it can be very hard - to keep track of the numbers in complicated patterns. Furthermore, if - an expression is modified, the numbers may change. To help with this - difficulty, PCRE2 supports the naming of capture groups. This feature - was not added to Perl until release 5.10. Python had the feature ear- - lier, and PCRE1 introduced it at release 4.0, using the Python syntax. + to keep track of the numbers in complicated patterns. Furthermore, if + an expression is modified, the numbers may change. To help with this + difficulty, PCRE2 supports the naming of capture groups. This feature + was not added to Perl until release 5.10. Python had the feature ear- + lier, and PCRE1 introduced it at release 4.0, using the Python syntax. PCRE2 supports both the Perl and the Python syntax. - In PCRE2, a capture group can be named in one of three ways: + In PCRE2, a capture group can be named in one of three ways: (? ...) or (?'name'...) as in Perl, or (?P ...) as in Python. - Names may be up to 32 code units long. When PCRE2_UTF is not set, they - may contain only ASCII alphanumeric characters and underscores, but + Names may be up to 32 code units long. When PCRE2_UTF is not set, they + may contain only ASCII alphanumeric characters and underscores, but must start with a non-digit. When PCRE2_UTF is set, the syntax of group names is extended to allow any Unicode letter or Unicode decimal digit. In other words, group names must match one of these patterns: @@ -7803,42 +7842,42 @@ NAMED CAPTURE GROUPS ^[_A-Za-z][_A-Za-z0-9]*\z when PCRE2_UTF is not set ^[_\p{L}][_\p{L}\p{Nd}]*\z when PCRE2_UTF is set - References to capture groups from other parts of the pattern, such as - backreferences, recursion, and conditions, can all be made by name as + References to capture groups from other parts of the pattern, such as + backreferences, recursion, and conditions, can all be made by name as well as by number. Named capture groups are allocated numbers as well as names, exactly as - if the names were not present. In both PCRE2 and Perl, capture groups - are primarily identified by numbers; any names are just aliases for + if the names were not present. In both PCRE2 and Perl, capture groups + are primarily identified by numbers; any names are just aliases for these numbers. The PCRE2 API provides function calls for extracting the - complete name-to-number translation table from a compiled pattern, as - well as convenience functions for extracting captured substrings by + complete name-to-number translation table from a compiled pattern, as + well as convenience functions for extracting captured substrings by name. - Warning: When more than one capture group has the same number, as de- + Warning: When more than one capture group has the same number, as de- scribed in the previous section, a name given to one of them applies to - all of them. Perl allows identically numbered groups to have different + all of them. Perl allows identically numbered groups to have different names. Consider this pattern, where there are two capture groups, both numbered 1: (?|(? aa)|(? bb)) - Perl allows this, with both names AA and BB as aliases of group 1. + Perl allows this, with both names AA and BB as aliases of group 1. Thus, after a successful match, both names yield the same value (either "aa" or "bb"). - In an attempt to reduce confusion, PCRE2 does not allow the same group + In an attempt to reduce confusion, PCRE2 does not allow the same group number to be associated with more than one name. The example above pro- - vokes a compile-time error. However, there is still scope for confu- + vokes a compile-time error. However, there is still scope for confu- sion. Consider this pattern: (?|(? aa)|(bb)) Although the second group number 1 is not explicitly named, the name AA - is still an alias for any group 1. Whether the pattern matches "aa" or + is still an alias for any group 1. Whether the pattern matches "aa" or "bb", a reference by name to group AA yields the matched string. - By default, a name must be unique within a pattern, except that dupli- + By default, a name must be unique within a pattern, except that dupli- cate names are permitted for groups with the same number, for example: (?|(? aa)|(? bb)) @@ -7847,10 +7886,10 @@ NAMED CAPTURE GROUPS NAMES option at compile time, or by the use of (?J) within the pattern, as described in the section entitled "Internal Option Setting" above. - Duplicate names can be useful for patterns where only one instance of - the named capture group can match. Suppose you want to match the name - of a weekday, either as a 3-letter abbreviation or as the full name, - and in both cases you want to extract the abbreviation. This pattern + Duplicate names can be useful for patterns where only one instance of + the named capture group can match. Suppose you want to match the name + of a weekday, either as a 3-letter abbreviation or as the full name, + and in both cases you want to extract the abbreviation. This pattern (ignoring the line breaks) does the job: (?J) @@ -7860,17 +7899,17 @@ NAMED CAPTURE GROUPS (? Thu)(?:rsday)?| (? Sat)(?:urday)? - There are five capture groups, but only one is ever set after a match. - The convenience functions for extracting the data by name returns the - substring for the first (and in this example, the only) group of that + There are five capture groups, but only one is ever set after a match. + The convenience functions for extracting the data by name returns the + substring for the first (and in this example, the only) group of that name that matched. This saves searching to find which numbered group it - was. (An alternative way of solving this problem is to use a "branch + was. (An alternative way of solving this problem is to use a "branch reset" group, as described in the previous section.) - If you make a backreference to a non-unique named group from elsewhere - in the pattern, the groups to which the name refers are checked in the - order in which they appear in the overall pattern. The first one that - is set is used for the reference. For example, this pattern matches + If you make a backreference to a non-unique named group from elsewhere + in the pattern, the groups to which the name refers are checked in the + order in which they appear in the overall pattern. The first one that + is set is used for the reference. For example, this pattern matches both "foofoo" and "barbar" but not "foobar" or "barfoo": (?J)(?:(? foo)|(? bar))\k @@ -7883,15 +7922,15 @@ NAMED CAPTURE GROUPS If you use a named reference in a condition test (see the section about conditions below), either to check whether a capture group has matched, or to check for recursion, all groups with the same name are tested. If - the condition is true for any one of them, the overall condition is - true. This is the same behaviour as testing by number. For further de- - tails of the interfaces for handling named capture groups, see the + the condition is true for any one of them, the overall condition is + true. This is the same behaviour as testing by number. For further de- + tails of the interfaces for handling named capture groups, see the pcre2api documentation. REPETITION - Repetition is specified by quantifiers, which can follow any of the + Repetition is specified by quantifiers, which can follow any of the following items: a literal data character @@ -7905,17 +7944,17 @@ REPETITION a parenthesized group (including lookaround assertions) a subroutine call (recursive or otherwise) - The general repetition quantifier specifies a minimum and maximum num- - ber of permitted matches, by giving the two numbers in curly brackets - (braces), separated by a comma. The numbers must be less than 65536, + The general repetition quantifier specifies a minimum and maximum num- + ber of permitted matches, by giving the two numbers in curly brackets + (braces), separated by a comma. The numbers must be less than 65536, and the first must be less than or equal to the second. For example, z{2,4} - matches "zz", "zzz", or "zzzz". A closing brace on its own is not a - special character. If the second number is omitted, but the comma is - present, there is no upper limit; if the second number and the comma - are both omitted, the quantifier specifies an exact number of required + matches "zz", "zzz", or "zzzz". A closing brace on its own is not a + special character. If the second number is omitted, but the comma is + present, there is no upper limit; if the second number and the comma + are both omitted, the quantifier specifies an exact number of required matches. Thus [aeiou]{3,} @@ -7924,53 +7963,53 @@ REPETITION \d{8} - matches exactly 8 digits. An opening curly bracket that appears in a - position where a quantifier is not allowed, or one that does not match - the syntax of a quantifier, is taken as a literal character. For exam- + matches exactly 8 digits. An opening curly bracket that appears in a + position where a quantifier is not allowed, or one that does not match + the syntax of a quantifier, is taken as a literal character. For exam- ple, {,6} is not a quantifier, but a literal string of four characters. In UTF modes, quantifiers apply to characters rather than to individual - code units. Thus, for example, \x{100}{2} matches two characters, each + code units. Thus, for example, \x{100}{2} matches two characters, each of which is represented by a two-byte sequence in a UTF-8 string. Simi- - larly, \X{3} matches three Unicode extended grapheme clusters, each of - which may be several code units long (and they may be of different + larly, \X{3} matches three Unicode extended grapheme clusters, each of + which may be several code units long (and they may be of different lengths). The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. This may be use- - ful for capture groups that are referenced as subroutines from else- - where in the pattern (but see also the section entitled "Defining cap- + ful for capture groups that are referenced as subroutines from else- + where in the pattern (but see also the section entitled "Defining cap- ture groups for use by reference only" below). Except for parenthesized - groups, items that have a {0} quantifier are omitted from the compiled + groups, items that have a {0} quantifier are omitted from the compiled pattern. - For convenience, the three most common quantifiers have single-charac- + For convenience, the three most common quantifiers have single-charac- ter abbreviations: * is equivalent to {0,} + is equivalent to {1,} ? is equivalent to {0,1} - It is possible to construct infinite loops by following a group that - can match no characters with a quantifier that has no upper limit, for + It is possible to construct infinite loops by following a group that + can match no characters with a quantifier that has no upper limit, for example: (a?)* - Earlier versions of Perl and PCRE1 used to give an error at compile + Earlier versions of Perl and PCRE1 used to give an error at compile time for such patterns. However, because there are cases where this can be useful, such patterns are now accepted, but whenever an iteration of - such a group matches no characters, matching moves on to the next item - in the pattern instead of repeatedly matching an empty string. This - does not prevent backtracking into any of the iterations if a subse- + such a group matches no characters, matching moves on to the next item + in the pattern instead of repeatedly matching an empty string. This + does not prevent backtracking into any of the iterations if a subse- quent item fails to match. - By default, quantifiers are "greedy", that is, they match as much as + By default, quantifiers are "greedy", that is, they match as much as possible (up to the maximum number of permitted times), without causing - the rest of the pattern to fail. The classic example of where this - gives problems is in trying to match comments in C programs. These ap- + the rest of the pattern to fail. The classic example of where this + gives problems is in trying to match comments in C programs. These ap- pear between /* and */ and within the comment, individual * and / char- - acters may appear. An attempt to match C comments by applying the pat- + acters may appear. An attempt to match C comments by applying the pat- tern /\*.*\*/ @@ -7979,17 +8018,17 @@ REPETITION /* first comment */ not comment /* second comment */ - fails, because it matches the entire string owing to the greediness of - the .* item. However, if a quantifier is followed by a question mark, + fails, because it matches the entire string owing to the greediness of + the .* item. However, if a quantifier is followed by a question mark, it ceases to be greedy, and instead matches the minimum number of times possible, so the pattern /\*.*?\*/ - does the right thing with the C comments. The meaning of the various - quantifiers is not otherwise changed, just the preferred number of - matches. Do not confuse this use of question mark with its use as a - quantifier in its own right. Because it has two uses, it can sometimes + does the right thing with the C comments. The meaning of the various + quantifiers is not otherwise changed, just the preferred number of + matches. Do not confuse this use of question mark with its use as a + quantifier in its own right. Because it has two uses, it can sometimes appear doubled, as in \d??\d @@ -7998,55 +8037,55 @@ REPETITION only way the rest of the pattern matches. If the PCRE2_UNGREEDY option is set (an option that is not available in - Perl), the quantifiers are not greedy by default, but individual ones - can be made greedy by following them with a question mark. In other + Perl), the quantifiers are not greedy by default, but individual ones + can be made greedy by following them with a question mark. In other words, it inverts the default behaviour. - When a parenthesized group is quantified with a minimum repeat count - that is greater than 1 or with a limited maximum, more memory is re- + When a parenthesized group is quantified with a minimum repeat count + that is greater than 1 or with a limited maximum, more memory is re- quired for the compiled pattern, in proportion to the size of the mini- mum or maximum. - If a pattern starts with .* or .{0,} and the PCRE2_DOTALL option - (equivalent to Perl's /s) is set, thus allowing the dot to match new- - lines, the pattern is implicitly anchored, because whatever follows - will be tried against every character position in the subject string, - so there is no point in retrying the overall match at any position af- - ter the first. PCRE2 normally treats such a pattern as though it were + If a pattern starts with .* or .{0,} and the PCRE2_DOTALL option + (equivalent to Perl's /s) is set, thus allowing the dot to match new- + lines, the pattern is implicitly anchored, because whatever follows + will be tried against every character position in the subject string, + so there is no point in retrying the overall match at any position af- + ter the first. PCRE2 normally treats such a pattern as though it were preceded by \A. - In cases where it is known that the subject string contains no new- - lines, it is worth setting PCRE2_DOTALL in order to obtain this opti- + In cases where it is known that the subject string contains no new- + lines, it is worth setting PCRE2_DOTALL in order to obtain this opti- mization, or alternatively, using ^ to indicate anchoring explicitly. - However, there are some cases where the optimization cannot be used. - When .* is inside capturing parentheses that are the subject of a - backreference elsewhere in the pattern, a match at the start may fail + However, there are some cases where the optimization cannot be used. + When .* is inside capturing parentheses that are the subject of a + backreference elsewhere in the pattern, a match at the start may fail where a later one succeeds. Consider, for example: (.*)abc\1 - If the subject is "xyz123abc123" the match point is the fourth charac- + If the subject is "xyz123abc123" the match point is the fourth charac- ter. For this reason, such a pattern is not implicitly anchored. - Another case where implicit anchoring is not applied is when the lead- - ing .* is inside an atomic group. Once again, a match at the start may + Another case where implicit anchoring is not applied is when the lead- + ing .* is inside an atomic group. Once again, a match at the start may fail where a later one succeeds. Consider this pattern: (?>.*?a)b - It matches "ab" in the subject "aab". The use of the backtracking con- - trol verbs (*PRUNE) and (*SKIP) also disable this optimization, and + It matches "ab" in the subject "aab". The use of the backtracking con- + trol verbs (*PRUNE) and (*SKIP) also disable this optimization, and there is an option, PCRE2_NO_DOTSTAR_ANCHOR, to do so explicitly. - When a capture group is repeated, the value captured is the substring + When a capture group is repeated, the value captured is the substring that matched the final iteration. For example, after (tweedle[dume]{3}\s*)+ has matched "tweedledum tweedledee" the value of the captured substring - is "tweedledee". However, if there are nested capture groups, the cor- - responding captured values may have been set in previous iterations. + is "tweedledee". However, if there are nested capture groups, the cor- + responding captured values may have been set in previous iterations. For example, after (a|(b))+ @@ -8056,57 +8095,57 @@ REPETITION ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS - With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") - repetition, failure of what follows normally causes the repeated item - to be re-evaluated to see if a different number of repeats allows the - rest of the pattern to match. Sometimes it is useful to prevent this, - either to change the nature of the match, or to cause it fail earlier - than it otherwise might, when the author of the pattern knows there is + With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") + repetition, failure of what follows normally causes the repeated item + to be re-evaluated to see if a different number of repeats allows the + rest of the pattern to match. Sometimes it is useful to prevent this, + either to change the nature of the match, or to cause it fail earlier + than it otherwise might, when the author of the pattern knows there is no point in carrying on. - Consider, for example, the pattern \d+foo when applied to the subject + Consider, for example, the pattern \d+foo when applied to the subject line 123456bar After matching all 6 digits and then failing to match "foo", the normal - action of the matcher is to try again with only 5 digits matching the - \d+ item, and then with 4, and so on, before ultimately failing. - "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides + action of the matcher is to try again with only 5 digits matching the + \d+ item, and then with 4, and so on, before ultimately failing. + "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides the means for specifying that once a group has matched, it is not to be re-evaluated in this way. - If we use atomic grouping for the previous example, the matcher gives - up immediately on failing to match "foo" the first time. The notation + If we use atomic grouping for the previous example, the matcher gives + up immediately on failing to match "foo" the first time. The notation is a kind of special parenthesis, starting with (?> as in this example: (?>\d+)foo - Perl 5.28 introduced an experimental alphabetic form starting with (* + Perl 5.28 introduced an experimental alphabetic form starting with (* which may be easier to remember: (*atomic:\d+)foo - This kind of parenthesized group "locks up" the part of the pattern it + This kind of parenthesized group "locks up" the part of the pattern it contains once it has matched, and a failure further into the pattern is - prevented from backtracking into it. Backtracking past it to previous + prevented from backtracking into it. Backtracking past it to previous items, however, works as normal. An alternative description is that a group of this type matches exactly - the string of characters that an identical standalone pattern would + the string of characters that an identical standalone pattern would match, if anchored at the current point in the subject string. - Atomic groups are not capture groups. Simple cases such as the above - example can be thought of as a maximizing repeat that must swallow ev- - erything it can. So, while both \d+ and \d+? are prepared to adjust - the number of digits they match in order to make the rest of the pat- + Atomic groups are not capture groups. Simple cases such as the above + example can be thought of as a maximizing repeat that must swallow ev- + erything it can. So, while both \d+ and \d+? are prepared to adjust + the number of digits they match in order to make the rest of the pat- tern match, (?>\d+) can only match an entire sequence of digits. - Atomic groups in general can of course contain arbitrarily complicated + Atomic groups in general can of course contain arbitrarily complicated expressions, and can be nested. However, when the contents of an atomic - group is just a single repeated item, as in the example above, a sim- - pler notation, called a "possessive quantifier" can be used. This con- - sists of an additional + character following a quantifier. Using this + group is just a single repeated item, as in the example above, a sim- + pler notation, called a "possessive quantifier" can be used. This con- + sists of an additional + character following a quantifier. Using this notation, the previous example can be rewritten as \d++foo @@ -8116,46 +8155,46 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS (abc|xyz){2,3}+ - Possessive quantifiers are always greedy; the setting of the PCRE2_UN- - GREEDY option is ignored. They are a convenient notation for the sim- - pler forms of atomic group. However, there is no difference in the - meaning of a possessive quantifier and the equivalent atomic group, - though there may be a performance difference; possessive quantifiers + Possessive quantifiers are always greedy; the setting of the PCRE2_UN- + GREEDY option is ignored. They are a convenient notation for the sim- + pler forms of atomic group. However, there is no difference in the + meaning of a possessive quantifier and the equivalent atomic group, + though there may be a performance difference; possessive quantifiers should be slightly faster. - The possessive quantifier syntax is an extension to the Perl 5.8 syn- - tax. Jeffrey Friedl originated the idea (and the name) in the first + The possessive quantifier syntax is an extension to the Perl 5.8 syn- + tax. Jeffrey Friedl originated the idea (and the name) in the first edition of his book. Mike McCloskey liked it, so implemented it when he - built Sun's Java package, and PCRE1 copied it from there. It found its + built Sun's Java package, and PCRE1 copied it from there. It found its way into Perl at release 5.10. - PCRE2 has an optimization that automatically "possessifies" certain - simple pattern constructs. For example, the sequence A+B is treated as - A++B because there is no point in backtracking into a sequence of A's + PCRE2 has an optimization that automatically "possessifies" certain + simple pattern constructs. For example, the sequence A+B is treated as + A++B because there is no point in backtracking into a sequence of A's when B must follow. This feature can be disabled by the PCRE2_NO_AUTO- POSSESS option, or starting the pattern with (*NO_AUTO_POSSESS). When a pattern contains an unlimited repeat inside a group that can it- - self be repeated an unlimited number of times, the use of an atomic - group is the only way to avoid some failing matches taking a very long + self be repeated an unlimited number of times, the use of an atomic + group is the only way to avoid some failing matches taking a very long time indeed. The pattern (\D+|<\d+>)*[!?] - matches an unlimited number of substrings that either consist of non- - digits, or digits enclosed in <>, followed by either ! or ?. When it + matches an unlimited number of substrings that either consist of non- + digits, or digits enclosed in <>, followed by either ! or ?. When it matches, it runs quickly. However, if it is applied to aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa - it takes a long time before reporting failure. This is because the - string can be divided between the internal \D+ repeat and the external - * repeat in a large number of ways, and all have to be tried. (The ex- + it takes a long time before reporting failure. This is because the + string can be divided between the internal \D+ repeat and the external + * repeat in a large number of ways, and all have to be tried. (The ex- ample uses [!?] rather than a single character at the end, because both PCRE2 and Perl have an optimization that allows for fast failure when a - single character is used. They remember the last single character that - is required for a match, and fail early if it is not present in the - string.) If the pattern is changed so that it uses an atomic group, + single character is used. They remember the last single character that + is required for a match, and fail early if it is not present in the + string.) If the pattern is changed so that it uses an atomic group, like this: ((?>\D+)|<\d+>)*[!?] @@ -8166,28 +8205,28 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS BACKREFERENCES Outside a character class, a backslash followed by a digit greater than - 0 (and possibly further digits) is a backreference to a capture group + 0 (and possibly further digits) is a backreference to a capture group earlier (that is, to its left) in the pattern, provided there have been that many previous capture groups. - However, if the decimal number following the backslash is less than 8, - it is always taken as a backreference, and causes an error only if - there are not that many capture groups in the entire pattern. In other + However, if the decimal number following the backslash is less than 8, + it is always taken as a backreference, and causes an error only if + there are not that many capture groups in the entire pattern. In other words, the group that is referenced need not be to the left of the ref- - erence for numbers less than 8. A "forward backreference" of this type + erence for numbers less than 8. A "forward backreference" of this type can make sense when a repetition is involved and the group to the right has participated in an earlier iteration. - It is not possible to have a numerical "forward backreference" to a - group whose number is 8 or more using this syntax because a sequence - such as \50 is interpreted as a character defined in octal. See the + It is not possible to have a numerical "forward backreference" to a + group whose number is 8 or more using this syntax because a sequence + such as \50 is interpreted as a character defined in octal. See the subsection entitled "Non-printing characters" above for further details - of the handling of digits following a backslash. Other forms of back- - referencing do not suffer from this restriction. In particular, there + of the handling of digits following a backslash. Other forms of back- + referencing do not suffer from this restriction. In particular, there is no problem when named capture groups are used (see below). - Another way of avoiding the ambiguity inherent in the use of digits - following a backslash is to use the \g escape sequence. This escape + Another way of avoiding the ambiguity inherent in the use of digits + following a backslash is to use the \g escape sequence. This escape must be followed by a signed or unsigned number, optionally enclosed in braces. These examples are all identical: @@ -8195,9 +8234,9 @@ BACKREFERENCES (ring), \g1 (ring), \g{1} - An unsigned number specifies an absolute reference without the ambigu- + An unsigned number specifies an absolute reference without the ambigu- ity that is present in the older syntax. It is also useful when literal - digits follow the reference. A signed number is a relative reference. + digits follow the reference. A signed number is a relative reference. Consider this example: (abc(def)ghi)\g{-1} @@ -8205,36 +8244,36 @@ BACKREFERENCES The sequence \g{-1} is a reference to the most recently started capture group before \g, that is, is it equivalent to \2 in this example. Simi- larly, \g{-2} would be equivalent to \1. The use of relative references - can be helpful in long patterns, and also in patterns that are created - by joining together fragments that contain references within them- + can be helpful in long patterns, and also in patterns that are created + by joining together fragments that contain references within them- selves. The sequence \g{+1} is a reference to the next capture group. This kind - of forward reference can be useful in patterns that repeat. Perl does + of forward reference can be useful in patterns that repeat. Perl does not support the use of + in this way. - A backreference matches whatever actually most recently matched the - capture group in the current subject string, rather than anything at + A backreference matches whatever actually most recently matched the + capture group in the current subject string, rather than anything at all that matches the group (see "Groups as subroutines" below for a way of doing that). So the pattern (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but - not "sense and responsibility". If caseful matching is in force at the - time of the backreference, the case of letters is relevant. For exam- + matches "sense and sensibility" and "response and responsibility", but + not "sense and responsibility". If caseful matching is in force at the + time of the backreference, the case of letters is relevant. For exam- ple, ((?i)rah)\s+\1 - matches "rah rah" and "RAH RAH", but not "RAH rah", even though the + matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original capture group is matched caselessly. - There are several different ways of writing backreferences to named - capture groups. The .NET syntax \k{name} and the Perl syntax \k - or \k'name' are supported, as is the Python syntax (?P=name). Perl - 5.10's unified backreference syntax, in which \g can be used for both - numeric and named references, is also supported. We could rewrite the + There are several different ways of writing backreferences to named + capture groups. The .NET syntax \k{name} and the Perl syntax \k + or \k'name' are supported, as is the Python syntax (?P=name). Perl + 5.10's unified backreference syntax, in which \g can be used for both + numeric and named references, is also supported. We could rewrite the above example in any of the following ways: (? (?i)rah)\s+\k @@ -8242,114 +8281,114 @@ BACKREFERENCES (?P (?i)rah)\s+(?P=p1) (? (?i)rah)\s+\g{p1} - A capture group that is referenced by name may appear in the pattern + A capture group that is referenced by name may appear in the pattern before or after the reference. - There may be more than one backreference to the same group. If a group - has not actually been used in a particular match, backreferences to it + There may be more than one backreference to the same group. If a group + has not actually been used in a particular match, backreferences to it always fail by default. For example, the pattern (a|(bc))\2 - always fails if it starts to match "a" rather than "bc". However, if + always fails if it starts to match "a" rather than "bc". However, if the PCRE2_MATCH_UNSET_BACKREF option is set at compile time, a backref- erence to an unset value matches an empty string. - Because there may be many capture groups in a pattern, all digits fol- - lowing a backslash are taken as part of a potential backreference num- - ber. If the pattern continues with a digit character, some delimiter - must be used to terminate the backreference. If the PCRE2_EXTENDED or - PCRE2_EXTENDED_MORE option is set, this can be white space. Otherwise, + Because there may be many capture groups in a pattern, all digits fol- + lowing a backslash are taken as part of a potential backreference num- + ber. If the pattern continues with a digit character, some delimiter + must be used to terminate the backreference. If the PCRE2_EXTENDED or + PCRE2_EXTENDED_MORE option is set, this can be white space. Otherwise, the \g{} syntax or an empty comment (see "Comments" below) can be used. Recursive backreferences - A backreference that occurs inside the group to which it refers fails - when the group is first used, so, for example, (a\1) never matches. - However, such references can be useful inside repeated groups. For ex- + A backreference that occurs inside the group to which it refers fails + when the group is first used, so, for example, (a\1) never matches. + However, such references can be useful inside repeated groups. For ex- ample, the pattern (a|b\1)+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- ation of the group, the backreference matches the character string cor- - responding to the previous iteration. In order for this to work, the - pattern must be such that the first iteration does not need to match - the backreference. This can be done using alternation, as in the exam- + responding to the previous iteration. In order for this to work, the + pattern must be such that the first iteration does not need to match + the backreference. This can be done using alternation, as in the exam- ple above, or by a quantifier with a minimum of zero. For versions of PCRE2 less than 10.25, backreferences of this type used - to cause the group that they reference to be treated as an atomic - group. This restriction no longer applies, and backtracking into such + to cause the group that they reference to be treated as an atomic + group. This restriction no longer applies, and backtracking into such groups can occur as normal. ASSERTIONS - An assertion is a test on the characters following or preceding the + An assertion is a test on the characters following or preceding the current matching point that does not consume any characters. The simple - assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described + assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described above. - More complicated assertions are coded as parenthesized groups. There - are two kinds: those that look ahead of the current position in the - subject string, and those that look behind it, and in each case an as- - sertion may be positive (must match for the assertion to be true) or - negative (must not match for the assertion to be true). An assertion + More complicated assertions are coded as parenthesized groups. There + are two kinds: those that look ahead of the current position in the + subject string, and those that look behind it, and in each case an as- + sertion may be positive (must match for the assertion to be true) or + negative (must not match for the assertion to be true). An assertion group is matched in the normal way, and if it is true, matching contin- - ues after it, but with the matching position in the subject string re- + ues after it, but with the matching position in the subject string re- set to what it was before the assertion was processed. - The Perl-compatible lookaround assertions are atomic. If an assertion - is true, but there is a subsequent matching failure, there is no back- - tracking into the assertion. However, there are some cases where non- - atomic assertions can be useful. PCRE2 has some support for these, de- + The Perl-compatible lookaround assertions are atomic. If an assertion + is true, but there is a subsequent matching failure, there is no back- + tracking into the assertion. However, there are some cases where non- + atomic assertions can be useful. PCRE2 has some support for these, de- scribed in the section entitled "Non-atomic assertions" below, but they are not Perl-compatible. - A lookaround assertion may appear as the condition in a conditional - group (see below). In this case, the result of matching the assertion + A lookaround assertion may appear as the condition in a conditional + group (see below). In this case, the result of matching the assertion determines which branch of the condition is followed. - Assertion groups are not capture groups. If an assertion contains cap- - ture groups within it, these are counted for the purposes of numbering - the capture groups in the whole pattern. Within each branch of an as- - sertion, locally captured substrings may be referenced in the usual - way. For example, a sequence such as (.)\g{-1} can be used to check + Assertion groups are not capture groups. If an assertion contains cap- + ture groups within it, these are counted for the purposes of numbering + the capture groups in the whole pattern. Within each branch of an as- + sertion, locally captured substrings may be referenced in the usual + way. For example, a sequence such as (.)\g{-1} can be used to check that two adjacent characters are the same. - When a branch within an assertion fails to match, any substrings that - were captured are discarded (as happens with any pattern branch that - fails to match). A negative assertion is true only when all its + When a branch within an assertion fails to match, any substrings that + were captured are discarded (as happens with any pattern branch that + fails to match). A negative assertion is true only when all its branches fail to match; this means that no captured substrings are ever - retained after a successful negative assertion. When an assertion con- + retained after a successful negative assertion. When an assertion con- tains a matching branch, what happens depends on the type of assertion. - For a positive assertion, internally captured substrings in the suc- - cessful branch are retained, and matching continues with the next pat- - tern item after the assertion. For a negative assertion, a matching - branch means that the assertion is not true. If such an assertion is - being used as a condition in a conditional group (see below), captured - substrings are retained, because matching continues with the "no" + For a positive assertion, internally captured substrings in the suc- + cessful branch are retained, and matching continues with the next pat- + tern item after the assertion. For a negative assertion, a matching + branch means that the assertion is not true. If such an assertion is + being used as a condition in a conditional group (see below), captured + substrings are retained, because matching continues with the "no" branch of the condition. For other failing negative assertions, control passes to the previous backtracking point, thus discarding any captured strings within the assertion. - Most assertion groups may be repeated; though it makes no sense to as- + Most assertion groups may be repeated; though it makes no sense to as- sert the same thing several times, the side effect of capturing in pos- itive assertions may occasionally be useful. However, an assertion that - forms the condition for a conditional group may not be quantified. - PCRE2 used to restrict the repetition of assertions, but from release - 10.35 the only restriction is that an unlimited maximum repetition is - changed to be one more than the minimum. For example, {3,} is treated + forms the condition for a conditional group may not be quantified. + PCRE2 used to restrict the repetition of assertions, but from release + 10.35 the only restriction is that an unlimited maximum repetition is + changed to be one more than the minimum. For example, {3,} is treated as {3,4}. Alphabetic assertion names - Traditionally, symbolic sequences such as (?= and (?<= have been used - to specify lookaround assertions. Perl 5.28 introduced some experimen- + Traditionally, symbolic sequences such as (?= and (?<= have been used + to specify lookaround assertions. Perl 5.28 introduced some experimen- tal alphabetic alternatives which might be easier to remember. They all - start with (* instead of (? and must be written using lower case let- + start with (* instead of (? and must be written using lower case let- ters. PCRE2 supports the following synonyms: (*positive_lookahead: or (*pla: is the same as (?= @@ -8357,8 +8396,8 @@ ASSERTIONS (*positive_lookbehind: or (*plb: is the same as (?<= (*negative_lookbehind: or (*nlb: is the same as (? .*? \b\1\b ){2} - For a subject such as "word1 word2 word3 word2 word3 word4" the result - is "word3". How does it work? At the start, ^(?x) anchors the pattern + For a subject such as "word1 word2 word3 word2 word3 word4" the result + is "word3". How does it work? At the start, ^(?x) anchors the pattern and sets the "x" option, which causes white space (introduced for read- - ability) to be ignored. Inside the assertion, the greedy .* at first + ability) to be ignored. Inside the assertion, the greedy .* at first consumes the entire string, but then has to backtrack until the rest of - the assertion can match a word, which is captured by group 1. In other - words, when the assertion first succeeds, it captures the right-most + the assertion can match a word, which is captured by group 1. In other + words, when the assertion first succeeds, it captures the right-most word in the string. - The current matching point is then reset to the start of the subject, - and the rest of the pattern match checks for two occurrences of the - captured word, using an ungreedy .*? to scan from the left. If this - succeeds, we are done, but if the last word in the string does not oc- - cur twice, this part of the pattern fails. If a traditional atomic + The current matching point is then reset to the start of the subject, + and the rest of the pattern match checks for two occurrences of the + captured word, using an ungreedy .*? to scan from the left. If this + succeeds, we are done, but if the last word in the string does not oc- + cur twice, this part of the pattern fails. If a traditional atomic lookhead (?= or (*pla: had been used, the assertion could not be re-en- - tered, and the whole match would fail. The pattern would succeed only + tered, and the whole match would fail. The pattern would succeed only if the very last word in the subject was found twice. - Using a non-atomic lookahead, however, means that when the last word - does not occur twice in the string, the lookahead can backtrack and - find the second-last word, and so on, until either the match succeeds, + Using a non-atomic lookahead, however, means that when the last word + does not occur twice in the string, the lookahead can backtrack and + find the second-last word, and so on, until either the match succeeds, or all words have been tested. Two conditions must be met for a non-atomic assertion to be useful: the - contents of one or more capturing groups must change after a backtrack - into the assertion, and there must be a backreference to a changed - group later in the pattern. If this is not the case, the rest of the - pattern match fails exactly as before because nothing has changed, so + contents of one or more capturing groups must change after a backtrack + into the assertion, and there must be a backreference to a changed + group later in the pattern. If this is not the case, the rest of the + pattern match fails exactly as before because nothing has changed, so using a non-atomic assertion just wastes resources. - There is one exception to backtracking into a non-atomic assertion. If - an (*ACCEPT) control verb is triggered, the assertion succeeds atomi- - cally. That is, a subsequent match failure cannot backtrack into the + There is one exception to backtracking into a non-atomic assertion. If + an (*ACCEPT) control verb is triggered, the assertion succeeds atomi- + cally. That is, a subsequent match failure cannot backtrack into the assertion. - Non-atomic assertions are not supported by the alternative matching + Non-atomic assertions are not supported by the alternative matching function pcre2_dfa_match(). They are supported by JIT, but only if they do not contain any control verbs such as (*ACCEPT). (This may change in future). Note that assertions that appear as conditions for conditional @@ -8574,42 +8613,42 @@ NON-ATOMIC ASSERTIONS SCRIPT RUNS - In concept, a script run is a sequence of characters that are all from - the same Unicode script such as Latin or Greek. However, because some - scripts are commonly used together, and because some diacritical and - other marks are used with multiple scripts, it is not that simple. + In concept, a script run is a sequence of characters that are all from + the same Unicode script such as Latin or Greek. However, because some + scripts are commonly used together, and because some diacritical and + other marks are used with multiple scripts, it is not that simple. There is a full description of the rules that PCRE2 uses in the section entitled "Script Runs" in the pcre2unicode documentation. - If part of a pattern is enclosed between (*script_run: or (*sr: and a - closing parenthesis, it fails if the sequence of characters that it - matches are not a script run. After a failure, normal backtracking oc- - curs. Script runs can be used to detect spoofing attacks using charac- - ters that look the same, but are from different scripts. The string - "paypal.com" is an infamous example, where the letters could be a mix- + If part of a pattern is enclosed between (*script_run: or (*sr: and a + closing parenthesis, it fails if the sequence of characters that it + matches are not a script run. After a failure, normal backtracking oc- + curs. Script runs can be used to detect spoofing attacks using charac- + ters that look the same, but are from different scripts. The string + "paypal.com" is an infamous example, where the letters could be a mix- ture of Latin and Cyrillic. This pattern ensures that the matched char- acters in a sequence of non-spaces that follow white space are a script run: \s+(*sr:\S+) - To be sure that they are all from the Latin script (for example), a + To be sure that they are all from the Latin script (for example), a lookahead can be used: \s+(?=\p{Latin})(*sr:\S+) This works as long as the first character is expected to be a character - in that script, and not (for example) punctuation, which is allowed - with any script. If this is not the case, a more creative lookahead is - needed. For example, if digits, underscore, and dots are permitted at + in that script, and not (for example) punctuation, which is allowed + with any script. If this is not the case, a more creative lookahead is + needed. For example, if digits, underscore, and dots are permitted at the start: \s+(?=[0-9_.]*\p{Latin})(*sr:\S+) - In many cases, backtracking into a script run pattern fragment is not - desirable. The script run can employ an atomic group to prevent this. - Because this is a common requirement, a shorthand notation is provided + In many cases, backtracking into a script run pattern fragment is not + desirable. The script run can employ an atomic group to prevent this. + Because this is a common requirement, a shorthand notation is provided by (*atomic_script_run: or (*asr: (*asr:...) is the same as (*sr:(?>...)) @@ -8617,13 +8656,13 @@ SCRIPT RUNS Note that the atomic group is inside the script run. Putting it outside would not prevent backtracking into the script run pattern. - Support for script runs is not available if PCRE2 is compiled without + Support for script runs is not available if PCRE2 is compiled without Unicode support. A compile-time error is given if any of the above con- - structs is encountered. Script runs are not supported by the alternate - matching function, pcre2_dfa_match() because they use the same mecha- + structs is encountered. Script runs are not supported by the alternate + matching function, pcre2_dfa_match() because they use the same mecha- nism as capturing parentheses. - Warning: The (*ACCEPT) control verb (see below) should not be used + Warning: The (*ACCEPT) control verb (see below) should not be used within a script run group, because it causes an immediate exit from the group, bypassing the script run checking. @@ -8632,116 +8671,116 @@ CONDITIONAL GROUPS It is possible to cause the matching process to obey a pattern fragment conditionally or to choose between two alternative fragments, depending - on the result of an assertion, or whether a specific capture group has + on the result of an assertion, or whether a specific capture group has already been matched. The two possible forms of conditional group are: (?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern) - If the condition is satisfied, the yes-pattern is used; otherwise the - no-pattern (if present) is used. An absent no-pattern is equivalent to - an empty string (it always matches). If there are more than two alter- - natives in the group, a compile-time error occurs. Each of the two al- + If the condition is satisfied, the yes-pattern is used; otherwise the + no-pattern (if present) is used. An absent no-pattern is equivalent to + an empty string (it always matches). If there are more than two alter- + natives in the group, a compile-time error occurs. Each of the two al- ternatives may itself contain nested groups of any form, including con- - ditional groups; the restriction to two alternatives applies only at - the level of the condition itself. This pattern fragment is an example + ditional groups; the restriction to two alternatives applies only at + the level of the condition itself. This pattern fragment is an example where the alternatives are complex: (?(1) (A|B|C) | (D | (?(2)E|F) | E) ) There are five kinds of condition: references to capture groups, refer- - ences to recursion, two pseudo-conditions called DEFINE and VERSION, + ences to recursion, two pseudo-conditions called DEFINE and VERSION, and assertions. Checking for a used capture group by number - If the text between the parentheses consists of a sequence of digits, - the condition is true if a capture group of that number has previously - matched. If there is more than one capture group with the same number - (see the earlier section about duplicate group numbers), the condition + If the text between the parentheses consists of a sequence of digits, + the condition is true if a capture group of that number has previously + matched. If there is more than one capture group with the same number + (see the earlier section about duplicate group numbers), the condition is true if any of them have matched. An alternative notation is to pre- cede the digits with a plus or minus sign. In this case, the group num- - ber is relative rather than absolute. The most recently opened capture - group can be referenced by (?(-1), the next most recent by (?(-2), and - so on. Inside loops it can also make sense to refer to subsequent - groups. The next capture group can be referenced as (?(+1), and so on. - (The value zero in any of these forms is not used; it provokes a com- + ber is relative rather than absolute. The most recently opened capture + group can be referenced by (?(-1), the next most recent by (?(-2), and + so on. Inside loops it can also make sense to refer to subsequent + groups. The next capture group can be referenced as (?(+1), and so on. + (The value zero in any of these forms is not used; it provokes a com- pile-time error.) - Consider the following pattern, which contains non-significant white - space to make it more readable (assume the PCRE2_EXTENDED option) and + Consider the following pattern, which contains non-significant white + space to make it more readable (assume the PCRE2_EXTENDED option) and to divide it into three parts for ease of discussion: ( \( )? [^()]+ (?(1) \) ) - The first part matches an optional opening parenthesis, and if that + The first part matches an optional opening parenthesis, and if that character is present, sets it as the first captured substring. The sec- - ond part matches one or more characters that are not parentheses. The - third part is a conditional group that tests whether or not the first - capture group matched. If it did, that is, if subject started with an - opening parenthesis, the condition is true, and so the yes-pattern is - executed and a closing parenthesis is required. Otherwise, since no- + ond part matches one or more characters that are not parentheses. The + third part is a conditional group that tests whether or not the first + capture group matched. If it did, that is, if subject started with an + opening parenthesis, the condition is true, and so the yes-pattern is + executed and a closing parenthesis is required. Otherwise, since no- pattern is not present, the conditional group matches nothing. In other - words, this pattern matches a sequence of non-parentheses, optionally + words, this pattern matches a sequence of non-parentheses, optionally enclosed in parentheses. - If you were embedding this pattern in a larger one, you could use a + If you were embedding this pattern in a larger one, you could use a relative reference: ...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... - This makes the fragment independent of the parentheses in the larger + This makes the fragment independent of the parentheses in the larger pattern. Checking for a used capture group by name - Perl uses the syntax (?( )...) or (?('name')...) to test for a - used capture group by name. For compatibility with earlier versions of - PCRE1, which had this facility before Perl, the syntax (?(name)...) is - also recognized. Note, however, that undelimited names consisting of - the letter R followed by digits are ambiguous (see the following sec- + Perl uses the syntax (?( )...) or (?('name')...) to test for a + used capture group by name. For compatibility with earlier versions of + PCRE1, which had this facility before Perl, the syntax (?(name)...) is + also recognized. Note, however, that undelimited names consisting of + the letter R followed by digits are ambiguous (see the following sec- tion). Rewriting the above example to use a named group gives this: (? \( )? [^()]+ (?( ) \) ) - If the name used in a condition of this kind is a duplicate, the test - is applied to all groups of the same name, and is true if any one of + If the name used in a condition of this kind is a duplicate, the test + is applied to all groups of the same name, and is true if any one of them has matched. Checking for pattern recursion - "Recursion" in this sense refers to any subroutine-like call from one - part of the pattern to another, whether or not it is actually recur- - sive. See the sections entitled "Recursive patterns" and "Groups as + "Recursion" in this sense refers to any subroutine-like call from one + part of the pattern to another, whether or not it is actually recur- + sive. See the sections entitled "Recursive patterns" and "Groups as subroutines" below for details of recursion and subroutine calls. - If a condition is the string (R), and there is no capture group with - the name R, the condition is true if matching is currently in a recur- - sion or subroutine call to the whole pattern or any capture group. If - digits follow the letter R, and there is no group with that name, the - condition is true if the most recent call is into a group with the - given number, which must exist somewhere in the overall pattern. This + If a condition is the string (R), and there is no capture group with + the name R, the condition is true if matching is currently in a recur- + sion or subroutine call to the whole pattern or any capture group. If + digits follow the letter R, and there is no group with that name, the + condition is true if the most recent call is into a group with the + given number, which must exist somewhere in the overall pattern. This is a contrived example that is equivalent to a+b: ((?(R1)a+|(?1)b)) - However, in both cases, if there is a capture group with a matching - name, the condition tests for its being set, as described in the sec- - tion above, instead of testing for recursion. For example, creating a - group with the name R1 by adding (? ) to the above pattern com- + However, in both cases, if there is a capture group with a matching + name, the condition tests for its being set, as described in the sec- + tion above, instead of testing for recursion. For example, creating a + group with the name R1 by adding (? ) to the above pattern com- pletely changes its meaning. If a name preceded by ampersand follows the letter R, for example: (?(R&name)...) - the condition is true if the most recent recursion is into a group of + the condition is true if the most recent recursion is into a group of that name (which must exist within the pattern). This condition does not check the entire recursion stack. It tests only - the current level. If the name used in a condition of this kind is a - duplicate, the test is applied to all groups of the same name, and is + the current level. If the name used in a condition of this kind is a + duplicate, the test is applied to all groups of the same name, and is true if any one of them is the most recent recursion. At "top level", all these recursion test conditions are false. @@ -8749,111 +8788,111 @@ CONDITIONAL GROUPS Defining capture groups for use by reference only If the condition is the string (DEFINE), the condition is always false, - even if there is a group with the name DEFINE. In this case, there may + even if there is a group with the name DEFINE. In this case, there may be only one alternative in the rest of the conditional group. It is al- - ways skipped if control reaches this point in the pattern; the idea of - DEFINE is that it can be used to define subroutines that can be refer- - enced from elsewhere. (The use of subroutines is described below.) For - example, a pattern to match an IPv4 address such as "192.168.23.245" + ways skipped if control reaches this point in the pattern; the idea of + DEFINE is that it can be used to define subroutines that can be refer- + enced from elsewhere. (The use of subroutines is described below.) For + example, a pattern to match an IPv4 address such as "192.168.23.245" could be written like this (ignore white space and line breaks): (?(DEFINE) (? 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) \b (?&byte) (\.(?&byte)){3} \b - The first part of the pattern is a DEFINE group inside which another - group named "byte" is defined. This matches an individual component of - an IPv4 address (a number less than 256). When matching takes place, - this part of the pattern is skipped because DEFINE acts like a false - condition. The rest of the pattern uses references to the named group - to match the four dot-separated components of an IPv4 address, insist- + The first part of the pattern is a DEFINE group inside which another + group named "byte" is defined. This matches an individual component of + an IPv4 address (a number less than 256). When matching takes place, + this part of the pattern is skipped because DEFINE acts like a false + condition. The rest of the pattern uses references to the named group + to match the four dot-separated components of an IPv4 address, insist- ing on a word boundary at each end. Checking the PCRE2 version - Programs that link with a PCRE2 library can check the version by call- - ing pcre2_config() with appropriate arguments. Users of applications - that do not have access to the underlying code cannot do this. A spe- - cial "condition" called VERSION exists to allow such users to discover + Programs that link with a PCRE2 library can check the version by call- + ing pcre2_config() with appropriate arguments. Users of applications + that do not have access to the underlying code cannot do this. A spe- + cial "condition" called VERSION exists to allow such users to discover which version of PCRE2 they are dealing with by using this condition to - match a string such as "yesno". VERSION must be followed either by "=" + match a string such as "yesno". VERSION must be followed either by "=" or ">=" and a version number. For example: (?(VERSION>=10.4)yes|no) - This pattern matches "yes" if the PCRE2 version is greater or equal to - 10.4, or "no" otherwise. The fractional part of the version number may + This pattern matches "yes" if the PCRE2 version is greater or equal to + 10.4, or "no" otherwise. The fractional part of the version number may not contain more than two digits. Assertion conditions - If the condition is not in any of the above formats, it must be a - parenthesized assertion. This may be a positive or negative lookahead - or lookbehind assertion. However, it must be a traditional atomic as- + If the condition is not in any of the above formats, it must be a + parenthesized assertion. This may be a positive or negative lookahead + or lookbehind assertion. However, it must be a traditional atomic as- sertion, not one of the PCRE2-specific non-atomic assertions. - Consider this pattern, again containing non-significant white space, + Consider this pattern, again containing non-significant white space, and with the two alternatives on the second line: (?(?=[^a-z]*[a-z]) \d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) - The condition is a positive lookahead assertion that matches an op- + The condition is a positive lookahead assertion that matches an op- tional sequence of non-letters followed by a letter. In other words, it tests for the presence of at least one letter in the subject. If a let- - ter is found, the subject is matched against the first alternative; - otherwise it is matched against the second. This pattern matches - strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are + ter is found, the subject is matched against the first alternative; + otherwise it is matched against the second. This pattern matches + strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits. When an assertion that is a condition contains capture groups, any cap- - turing that occurs in a matching branch is retained afterwards, for - both positive and negative assertions, because matching always contin- - ues after the assertion, whether it succeeds or fails. (Compare non- - conditional assertions, for which captures are retained only for posi- + turing that occurs in a matching branch is retained afterwards, for + both positive and negative assertions, because matching always contin- + ues after the assertion, whether it succeeds or fails. (Compare non- + conditional assertions, for which captures are retained only for posi- tive assertions that succeed.) COMMENTS There are two ways of including comments in patterns that are processed - by PCRE2. In both cases, the start of the comment must not be in a - character class, nor in the middle of any other sequence of related - characters such as (?: or a group name or number. The characters that + by PCRE2. In both cases, the start of the comment must not be in a + character class, nor in the middle of any other sequence of related + characters such as (?: or a group name or number. The characters that make up a comment play no part in the pattern matching. - The sequence (?# marks the start of a comment that continues up to the - next closing parenthesis. Nested parentheses are not permitted. If the - PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set, an unescaped # - character also introduces a comment, which in this case continues to - immediately after the next newline character or character sequence in + The sequence (?# marks the start of a comment that continues up to the + next closing parenthesis. Nested parentheses are not permitted. If the + PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set, an unescaped # + character also introduces a comment, which in this case continues to + immediately after the next newline character or character sequence in the pattern. Which characters are interpreted as newlines is controlled - by an option passed to the compiling function or by a special sequence + by an option passed to the compiling function or by a special sequence at the start of the pattern, as described in the section entitled "New- line conventions" above. Note that the end of this type of comment is a - literal newline sequence in the pattern; escape sequences that happen + literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count. For example, consider this pattern - when PCRE2_EXTENDED is set, and the default newline convention (a sin- + when PCRE2_EXTENDED is set, and the default newline convention (a sin- gle linefeed character) is in force: abc #comment \n still comment - On encountering the # character, pcre2_compile() skips along, looking - for a newline in the pattern. The sequence \n is still literal at this - stage, so it does not terminate the comment. Only an actual character + On encountering the # character, pcre2_compile() skips along, looking + for a newline in the pattern. The sequence \n is still literal at this + stage, so it does not terminate the comment. Only an actual character with the code value 0x0a (the default newline) does so. RECURSIVE PATTERNS - Consider the problem of matching a string in parentheses, allowing for - unlimited nested parentheses. Without the use of recursion, the best - that can be done is to use a pattern that matches up to some fixed - depth of nesting. It is not possible to handle an arbitrary nesting + Consider the problem of matching a string in parentheses, allowing for + unlimited nested parentheses. Without the use of recursion, the best + that can be done is to use a pattern that matches up to some fixed + depth of nesting. It is not possible to handle an arbitrary nesting depth. For some time, Perl has provided a facility that allows regular expres- - sions to recurse (amongst other things). It does this by interpolating - Perl code in the expression at run time, and the code can refer to the + sions to recurse (amongst other things). It does this by interpolating + Perl code in the expression at run time, and the code can refer to the expression itself. A Perl pattern using code interpolation to solve the parentheses problem can be created like this: @@ -8862,67 +8901,67 @@ RECURSIVE PATTERNS The (?p{...}) item interpolates Perl code at run time, and in this case refers recursively to the pattern in which it appears. - Obviously, PCRE2 cannot support the interpolation of Perl code. In- - stead, it supports special syntax for recursion of the entire pattern, + Obviously, PCRE2 cannot support the interpolation of Perl code. In- + stead, it supports special syntax for recursion of the entire pattern, and also for individual capture group recursion. After its introduction in PCRE1 and Python, this kind of recursion was subsequently introduced into Perl at release 5.10. - A special item that consists of (? followed by a number greater than - zero and a closing parenthesis is a recursive subroutine call of the - capture group of the given number, provided that it occurs inside that - group. (If not, it is a non-recursive subroutine call, which is de- + A special item that consists of (? followed by a number greater than + zero and a closing parenthesis is a recursive subroutine call of the + capture group of the given number, provided that it occurs inside that + group. (If not, it is a non-recursive subroutine call, which is de- scribed in the next section.) The special item (?R) or (?0) is a recur- sive call of the entire regular expression. - This PCRE2 pattern solves the nested parentheses problem (assume the + This PCRE2 pattern solves the nested parentheses problem (assume the PCRE2_EXTENDED option is set so that white space is ignored): \( ( [^()]++ | (?R) )* \) - First it matches an opening parenthesis. Then it matches any number of - substrings which can either be a sequence of non-parentheses, or a re- + First it matches an opening parenthesis. Then it matches any number of + substrings which can either be a sequence of non-parentheses, or a re- cursive match of the pattern itself (that is, a correctly parenthesized - substring). Finally there is a closing parenthesis. Note the use of a - possessive quantifier to avoid backtracking into sequences of non- + substring). Finally there is a closing parenthesis. Note the use of a + possessive quantifier to avoid backtracking into sequences of non- parentheses. - If this were part of a larger pattern, you would not want to recurse + If this were part of a larger pattern, you would not want to recurse the entire pattern, so instead you could use this: ( \( ( [^()]++ | (?1) )* \) ) - We have put the pattern into parentheses, and caused the recursion to + We have put the pattern into parentheses, and caused the recursion to refer to them instead of the whole pattern. - In a larger pattern, keeping track of parenthesis numbers can be - tricky. This is made easier by the use of relative references. Instead + In a larger pattern, keeping track of parenthesis numbers can be + tricky. This is made easier by the use of relative references. Instead of (?1) in the pattern above you can write (?-2) to refer to the second - most recently opened parentheses preceding the recursion. In other - words, a negative number counts capturing parentheses leftwards from + most recently opened parentheses preceding the recursion. In other + words, a negative number counts capturing parentheses leftwards from the point at which it is encountered. - Be aware however, that if duplicate capture group numbers are in use, - relative references refer to the earliest group with the appropriate + Be aware however, that if duplicate capture group numbers are in use, + relative references refer to the earliest group with the appropriate number. Consider, for example: (?|(a)|(b)) (c) (?-2) The first two capture groups (a) and (b) are both numbered 1, and group - (c) is number 2. When the reference (?-2) is encountered, the second - most recently opened parentheses has the number 1, but it is the first + (c) is number 2. When the reference (?-2) is encountered, the second + most recently opened parentheses has the number 1, but it is the first such group (the (a) group) to which the recursion refers. This would be - the same if an absolute reference (?1) was used. In other words, rela- + the same if an absolute reference (?1) was used. In other words, rela- tive references are just a shorthand for computing a group number. - It is also possible to refer to subsequent capture groups, by writing - references such as (?+2). However, these cannot be recursive because - the reference is not inside the parentheses that are referenced. They - are always non-recursive subroutine calls, as described in the next + It is also possible to refer to subsequent capture groups, by writing + references such as (?+2). However, these cannot be recursive because + the reference is not inside the parentheses that are referenced. They + are always non-recursive subroutine calls, as described in the next section. - An alternative approach is to use named parentheses. The Perl syntax - for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup- + An alternative approach is to use named parentheses. The Perl syntax + for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup- ported. We could rewrite the above example as follows: (? \( ( [^()]++ | (?&pn) )* \) ) @@ -8931,57 +8970,57 @@ RECURSIVE PATTERNS used. The example pattern that we have been looking at contains nested unlim- - ited repeats, and so the use of a possessive quantifier for matching - strings of non-parentheses is important when applying the pattern to + ited repeats, and so the use of a possessive quantifier for matching + strings of non-parentheses is important when applying the pattern to strings that do not match. For example, when this pattern is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() - it yields "no match" quickly. However, if a possessive quantifier is - not used, the match runs for a very long time indeed because there are - so many different ways the + and * repeats can carve up the subject, + it yields "no match" quickly. However, if a possessive quantifier is + not used, the match runs for a very long time indeed because there are + so many different ways the + and * repeats can carve up the subject, and all have to be tested before failure can be reported. - At the end of a match, the values of capturing parentheses are those - from the outermost level. If you want to obtain intermediate values, a + At the end of a match, the values of capturing parentheses are those + from the outermost level. If you want to obtain intermediate values, a callout function can be used (see below and the pcre2callout documenta- tion). If the pattern above is matched against (ab(cd)ef) - the value for the inner capturing parentheses (numbered 2) is "ef", - which is the last value taken on at the top level. If a capture group - is not matched at the top level, its final captured value is unset, - even if it was (temporarily) set at a deeper level during the matching + the value for the inner capturing parentheses (numbered 2) is "ef", + which is the last value taken on at the top level. If a capture group + is not matched at the top level, its final captured value is unset, + even if it was (temporarily) set at a deeper level during the matching process. - Do not confuse the (?R) item with the condition (R), which tests for - recursion. Consider this pattern, which matches text in angle brack- - ets, allowing for arbitrary nesting. Only digits are allowed in nested - brackets (that is, when recursing), whereas any characters are permit- + Do not confuse the (?R) item with the condition (R), which tests for + recursion. Consider this pattern, which matches text in angle brack- + ets, allowing for arbitrary nesting. Only digits are allowed in nested + brackets (that is, when recursing), whereas any characters are permit- ted at the outer level. < (?: (?(R) \d++ | [^<>]*+) | (?R)) * > - In this pattern, (?(R) is the start of a conditional group, with two - different alternatives for the recursive and non-recursive cases. The + In this pattern, (?(R) is the start of a conditional group, with two + different alternatives for the recursive and non-recursive cases. The (?R) item is the actual recursive call. Differences in recursion processing between PCRE2 and Perl Some former differences between PCRE2 and Perl no longer exist. - Before release 10.30, recursion processing in PCRE2 differed from Perl - in that a recursive subroutine call was always treated as an atomic - group. That is, once it had matched some of the subject string, it was - never re-entered, even if it contained untried alternatives and there - was a subsequent matching failure. (Historical note: PCRE implemented + Before release 10.30, recursion processing in PCRE2 differed from Perl + in that a recursive subroutine call was always treated as an atomic + group. That is, once it had matched some of the subject string, it was + never re-entered, even if it contained untried alternatives and there + was a subsequent matching failure. (Historical note: PCRE implemented recursion before Perl did.) - Starting with release 10.30, recursive subroutine calls are no longer + Starting with release 10.30, recursive subroutine calls are no longer treated as atomic. That is, they can be re-entered to try unused alter- - natives if there is a matching failure later in the pattern. This is - now compatible with the way Perl works. If you want a subroutine call + natives if there is a matching failure later in the pattern. This is + now compatible with the way Perl works. If you want a subroutine call to be atomic, you must explicitly enclose it in an atomic group. Supporting backtracking into recursions simplifies certain types of re- @@ -8989,47 +9028,47 @@ RECURSIVE PATTERNS ^((.)(?1)\2|.?)$ - The second branch in the group matches a single central character in - the palindrome when there are an odd number of characters, or nothing - when there are an even number of characters, but in order to work it - has to be able to try the second case when the rest of the pattern + The second branch in the group matches a single central character in + the palindrome when there are an odd number of characters, or nothing + when there are an even number of characters, but in order to work it + has to be able to try the second case when the rest of the pattern match fails. If you want to match typical palindromic phrases, the pat- - tern has to ignore all non-word characters, which can be done like + tern has to ignore all non-word characters, which can be done like this: ^\W*+((.)\W*+(?1)\W*+\2|\W*+.?)\W*+$ - If run with the PCRE2_CASELESS option, this pattern matches phrases - such as "A man, a plan, a canal: Panama!". Note the use of the posses- - sive quantifier *+ to avoid backtracking into sequences of non-word + If run with the PCRE2_CASELESS option, this pattern matches phrases + such as "A man, a plan, a canal: Panama!". Note the use of the posses- + sive quantifier *+ to avoid backtracking into sequences of non-word characters. Without this, PCRE2 takes a great deal longer (ten times or - more) to match typical phrases, and Perl takes so long that you think + more) to match typical phrases, and Perl takes so long that you think it has gone into a loop. - Another way in which PCRE2 and Perl used to differ in their recursion - processing is in the handling of captured values. Formerly in Perl, - when a group was called recursively or as a subroutine (see the next + Another way in which PCRE2 and Perl used to differ in their recursion + processing is in the handling of captured values. Formerly in Perl, + when a group was called recursively or as a subroutine (see the next section), it had no access to any values that were captured outside the - recursion, whereas in PCRE2 these values can be referenced. Consider + recursion, whereas in PCRE2 these values can be referenced. Consider this pattern: ^(.)(\1|a(?2)) - This pattern matches "bab". The first capturing parentheses match "b", + This pattern matches "bab". The first capturing parentheses match "b", then in the second group, when the backreference \1 fails to match "b", the second alternative matches "a" and then recurses. In the recursion, - \1 does now match "b" and so the whole match succeeds. This match used + \1 does now match "b" and so the whole match succeeds. This match used to fail in Perl, but in later versions (I tried 5.024) it now works. GROUPS AS SUBROUTINES - If the syntax for a recursive group call (either by number or by name) - is used outside the parentheses to which it refers, it operates a bit - like a subroutine in a programming language. More accurately, PCRE2 + If the syntax for a recursive group call (either by number or by name) + is used outside the parentheses to which it refers, it operates a bit + like a subroutine in a programming language. More accurately, PCRE2 treats the referenced group as an independent subpattern which it tries - to match at the current matching position. The called group may be de- - fined before or after the reference. A numbered reference can be abso- + to match at the current matching position. The called group may be de- + fined before or after the reference. A numbered reference can be abso- lute or relative, as in these examples: (...(absolute)...)...(?2)... @@ -9040,106 +9079,106 @@ GROUPS AS SUBROUTINES (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but + matches "sense and sensibility" and "response and responsibility", but not "sense and responsibility". If instead the pattern (sens|respons)e and (?1)ibility - is used, it does match "sense and responsibility" as well as the other - two strings. Another example is given in the discussion of DEFINE + is used, it does match "sense and responsibility" as well as the other + two strings. Another example is given in the discussion of DEFINE above. - Like recursions, subroutine calls used to be treated as atomic, but - this changed at PCRE2 release 10.30, so backtracking into subroutine - calls can now occur. However, any capturing parentheses that are set + Like recursions, subroutine calls used to be treated as atomic, but + this changed at PCRE2 release 10.30, so backtracking into subroutine + calls can now occur. However, any capturing parentheses that are set during the subroutine call revert to their previous values afterwards. - Processing options such as case-independence are fixed when a group is - defined, so if it is used as a subroutine, such options cannot be + Processing options such as case-independence are fixed when a group is + defined, so if it is used as a subroutine, such options cannot be changed for different calls. For example, consider this pattern: (abc)(?i:(?-1)) - It matches "abcabc". It does not match "abcABC" because the change of + It matches "abcabc". It does not match "abcABC" because the change of processing option does not affect the called group. - The behaviour of backtracking control verbs in groups when called as + The behaviour of backtracking control verbs in groups when called as subroutines is described in the section entitled "Backtracking verbs in subroutines" below. ONIGURUMA SUBROUTINE SYNTAX - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is an alternative syntax for calling a group as a subroutine, possibly re- - cursively. Here are two of the examples used above, rewritten using + cursively. Here are two of the examples used above, rewritten using this syntax: (? \( ( (?>[^()]+) | \g )* \) ) (sens|respons)e and \g'1'ibility - PCRE2 supports an extension to Oniguruma: if a number is preceded by a + PCRE2 supports an extension to Oniguruma: if a number is preceded by a plus or a minus sign it is taken as a relative reference. For example: (abc)(?i:\g<-1>) - Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not - synonymous. The former is a backreference; the latter is a subroutine + Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not + synonymous. The former is a backreference; the latter is a subroutine call. CALLOUTS Perl has a feature whereby using the sequence (?{...}) causes arbitrary - Perl code to be obeyed in the middle of matching a regular expression. + Perl code to be obeyed in the middle of matching a regular expression. This makes it possible, amongst other things, to extract different sub- strings that match the same pair of parentheses when there is a repeti- tion. - PCRE2 provides a similar feature, but of course it cannot obey arbi- - trary Perl code. The feature is called "callout". The caller of PCRE2 - provides an external function by putting its entry point in a match - context using the function pcre2_set_callout(), and then passing that - context to pcre2_match() or pcre2_dfa_match(). If no match context is + PCRE2 provides a similar feature, but of course it cannot obey arbi- + trary Perl code. The feature is called "callout". The caller of PCRE2 + provides an external function by putting its entry point in a match + context using the function pcre2_set_callout(), and then passing that + context to pcre2_match() or pcre2_dfa_match(). If no match context is passed, or if the callout entry point is set to NULL, callouts are dis- abled. - Within a regular expression, (?C ) indicates a point at which the - external function is to be called. There are two kinds of callout: - those with a numerical argument and those with a string argument. (?C) - on its own with no argument is treated as (?C0). A numerical argument - allows the application to distinguish between different callouts. - String arguments were added for release 10.20 to make it possible for - script languages that use PCRE2 to embed short scripts within patterns + Within a regular expression, (?C ) indicates a point at which the + external function is to be called. There are two kinds of callout: + those with a numerical argument and those with a string argument. (?C) + on its own with no argument is treated as (?C0). A numerical argument + allows the application to distinguish between different callouts. + String arguments were added for release 10.20 to make it possible for + script languages that use PCRE2 to embed short scripts within patterns in a similar way to Perl. During matching, when PCRE2 reaches a callout point, the external func- - tion is called. It is provided with the number or string argument of - the callout, the position in the pattern, and one item of data that is + tion is called. It is provided with the number or string argument of + the callout, the position in the pattern, and one item of data that is also set in the match block. The callout function may cause matching to proceed, to backtrack, or to fail. - By default, PCRE2 implements a number of optimizations at matching - time, and one side-effect is that sometimes callouts are skipped. If - you need all possible callouts to happen, you need to set options that - disable the relevant optimizations. More details, including a complete - description of the programming interface to the callout function, are + By default, PCRE2 implements a number of optimizations at matching + time, and one side-effect is that sometimes callouts are skipped. If + you need all possible callouts to happen, you need to set options that + disable the relevant optimizations. More details, including a complete + description of the programming interface to the callout function, are given in the pcre2callout documentation. Callouts with numerical arguments - If you just want to have a means of identifying different callout - points, put a number less than 256 after the letter C. For example, + If you just want to have a means of identifying different callout + points, put a number less than 256 after the letter C. For example, this pattern has two callout points: (?C1)abc(?C2)def - If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical - callouts are automatically installed before each item in the pattern. - They are all numbered 255. If there is a conditional group in the pat- + If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical + callouts are automatically installed before each item in the pattern. + They are all numbered 255. If there is a conditional group in the pat- tern whose condition is an assertion, an additional callout is inserted - just before the condition. An explicit callout may also be set at this + just before the condition. An explicit callout may also be set at this position, as in this example: (?(?C9)(?=a)abc|def) @@ -9149,78 +9188,78 @@ CALLOUTS Callouts with string arguments - A delimited string may be used instead of a number as a callout argu- - ment. The starting delimiter must be one of ` ' " ^ % # $ { and the + A delimited string may be used instead of a number as a callout argu- + ment. The starting delimiter must be one of ` ' " ^ % # $ { and the ending delimiter is the same as the start, except for {, where the end- - ing delimiter is }. If the ending delimiter is needed within the + ing delimiter is }. If the ending delimiter is needed within the string, it must be doubled. For example: (?C'ab ''c'' d')xyz(?C{any text})pqr - The doubling is removed before the string is passed to the callout + The doubling is removed before the string is passed to the callout function. BACKTRACKING CONTROL - There are a number of special "Backtracking Control Verbs" (to use - Perl's terminology) that modify the behaviour of backtracking during - matching. They are generally of the form (*VERB) or (*VERB:NAME). Some + There are a number of special "Backtracking Control Verbs" (to use + Perl's terminology) that modify the behaviour of backtracking during + matching. They are generally of the form (*VERB) or (*VERB:NAME). Some verbs take either form, and may behave differently depending on whether - or not a name argument is present. The names are not required to be + or not a name argument is present. The names are not required to be unique within the pattern. - By default, for compatibility with Perl, a name is any sequence of + By default, for compatibility with Perl, a name is any sequence of characters that does not include a closing parenthesis. The name is not - processed in any way, and it is not possible to include a closing - parenthesis in the name. This can be changed by setting the - PCRE2_ALT_VERBNAMES option, but the result is no longer Perl-compati- + processed in any way, and it is not possible to include a closing + parenthesis in the name. This can be changed by setting the + PCRE2_ALT_VERBNAMES option, but the result is no longer Perl-compati- ble. - When PCRE2_ALT_VERBNAMES is set, backslash processing is applied to - verb names and only an unescaped closing parenthesis terminates the - name. However, the only backslash items that are permitted are \Q, \E, - and sequences such as \x{100} that define character code points. Char- + When PCRE2_ALT_VERBNAMES is set, backslash processing is applied to + verb names and only an unescaped closing parenthesis terminates the + name. However, the only backslash items that are permitted are \Q, \E, + and sequences such as \x{100} that define character code points. Char- acter type escapes such as \d are faulted. A closing parenthesis can be included in a name either as \) or between - \Q and \E. In addition to backslash processing, if the PCRE2_EXTENDED + \Q and \E. In addition to backslash processing, if the PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is also set, unescaped whitespace in verb names is skipped, and #-comments are recognized, exactly as in the rest - of the pattern. PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do not affect + of the pattern. PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do not affect verb names unless PCRE2_ALT_VERBNAMES is also set. - The maximum length of a name is 255 in the 8-bit library and 65535 in - the 16-bit and 32-bit libraries. If the name is empty, that is, if the - closing parenthesis immediately follows the colon, the effect is as if + The maximum length of a name is 255 in the 8-bit library and 65535 in + the 16-bit and 32-bit libraries. If the name is empty, that is, if the + closing parenthesis immediately follows the colon, the effect is as if the colon were not there. Any number of these verbs may occur in a pat- tern. Except for (*ACCEPT), they may not be quantified. - Since these verbs are specifically related to backtracking, most of - them can be used only when the pattern is to be matched using the tra- + Since these verbs are specifically related to backtracking, most of + them can be used only when the pattern is to be matched using the tra- ditional matching function, because that uses a backtracking algorithm. - With the exception of (*FAIL), which behaves like a failing negative + With the exception of (*FAIL), which behaves like a failing negative assertion, the backtracking control verbs cause an error if encountered by the DFA matching function. - The behaviour of these verbs in repeated groups, assertions, and in - capture groups called as subroutines (whether or not recursively) is + The behaviour of these verbs in repeated groups, assertions, and in + capture groups called as subroutines (whether or not recursively) is documented below. Optimizations that affect backtracking verbs PCRE2 contains some optimizations that are used to speed up matching by running some checks at the start of each match attempt. For example, it - may know the minimum length of matching subject, or that a particular + may know the minimum length of matching subject, or that a particular character must be present. When one of these optimizations bypasses the - running of a match, any included backtracking verbs will not, of + running of a match, any included backtracking verbs will not, of course, be processed. You can suppress the start-of-match optimizations - by setting the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com- - pile(), or by starting the pattern with (*NO_START_OPT). There is more + by setting the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com- + pile(), or by starting the pattern with (*NO_START_OPT). There is more discussion of this option in the section entitled "Compiling a pattern" in the pcre2api documentation. - Experiments with Perl suggest that it too has similar optimizations, + Experiments with Perl suggest that it too has similar optimizations, and like PCRE2, turning them off can change the result of a match. Verbs that act immediately @@ -9229,77 +9268,77 @@ BACKTRACKING CONTROL (*ACCEPT) or (*ACCEPT:NAME) - This verb causes the match to end successfully, skipping the remainder - of the pattern. However, when it is inside a capture group that is + This verb causes the match to end successfully, skipping the remainder + of the pattern. However, when it is inside a capture group that is called as a subroutine, only that group is ended successfully. Matching then continues at the outer level. If (*ACCEPT) in triggered in a posi- - tive assertion, the assertion succeeds; in a negative assertion, the + tive assertion, the assertion succeeds; in a negative assertion, the assertion fails. - If (*ACCEPT) is inside capturing parentheses, the data so far is cap- + If (*ACCEPT) is inside capturing parentheses, the data so far is cap- tured. For example: A((?:A|B(*ACCEPT)|C)D) - This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- + This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- tured by the outer parentheses. - (*ACCEPT) is the only backtracking verb that is allowed to be quanti- - fied because an ungreedy quantification with a minimum of zero acts + (*ACCEPT) is the only backtracking verb that is allowed to be quanti- + fied because an ungreedy quantification with a minimum of zero acts only when a backtrack happens. Consider, for example, (A(*ACCEPT)??B)C - where A, B, and C may be complex expressions. After matching "A", the - matcher processes "BC"; if that fails, causing a backtrack, (*ACCEPT) - is triggered and the match succeeds. In both cases, all but C is cap- - tured. Whereas (*COMMIT) (see below) means "fail on backtrack", a re- + where A, B, and C may be complex expressions. After matching "A", the + matcher processes "BC"; if that fails, causing a backtrack, (*ACCEPT) + is triggered and the match succeeds. In both cases, all but C is cap- + tured. Whereas (*COMMIT) (see below) means "fail on backtrack", a re- peated (*ACCEPT) of this type means "succeed on backtrack". - Warning: (*ACCEPT) should not be used within a script run group, be- - cause it causes an immediate exit from the group, bypassing the script + Warning: (*ACCEPT) should not be used within a script run group, be- + cause it causes an immediate exit from the group, bypassing the script run checking. (*FAIL) or (*FAIL:NAME) - This verb causes a matching failure, forcing backtracking to occur. It - may be abbreviated to (*F). It is equivalent to (?!) but easier to + This verb causes a matching failure, forcing backtracking to occur. It + may be abbreviated to (*F). It is equivalent to (?!) but easier to read. The Perl documentation notes that it is probably useful only when combined with (?{}) or (??{}). Those are, of course, Perl features that - are not present in PCRE2. The nearest equivalent is the callout fea- + are not present in PCRE2. The nearest equivalent is the callout fea- ture, as for example in this pattern: a+(?C)(*FAIL) - A match with the string "aaaa" always fails, but the callout is taken + A match with the string "aaaa" always fails, but the callout is taken before each backtrack happens (in this example, 10 times). - (*ACCEPT:NAME) and (*FAIL:NAME) behave the same as (*MARK:NAME)(*AC- - CEPT) and (*MARK:NAME)(*FAIL), respectively, that is, a (*MARK) is + (*ACCEPT:NAME) and (*FAIL:NAME) behave the same as (*MARK:NAME)(*AC- + CEPT) and (*MARK:NAME)(*FAIL), respectively, that is, a (*MARK) is recorded just before the verb acts. Recording which path was taken - There is one verb whose main purpose is to track how a match was ar- - rived at, though it also has a secondary use in conjunction with ad- + There is one verb whose main purpose is to track how a match was ar- + rived at, though it also has a secondary use in conjunction with ad- vancing the match starting point (see (*SKIP) below). (*MARK:NAME) or (*:NAME) - A name is always required with this verb. For all the other backtrack- + A name is always required with this verb. For all the other backtrack- ing control verbs, a NAME argument is optional. - When a match succeeds, the name of the last-encountered mark name on + When a match succeeds, the name of the last-encountered mark name on the matching path is passed back to the caller as described in the sec- tion entitled "Other information about the match" in the pcre2api docu- - mentation. This applies to all instances of (*MARK) and other verbs, + mentation. This applies to all instances of (*MARK) and other verbs, including those inside assertions and atomic groups. However, there are - differences in those cases when (*MARK) is used in conjunction with + differences in those cases when (*MARK) is used in conjunction with (*SKIP) as described below. - The mark name that was last encountered on the matching path is passed - back. A verb without a NAME argument is ignored for this purpose. Here - is an example of pcre2test output, where the "mark" modifier requests + The mark name that was last encountered on the matching path is passed + back. A verb without a NAME argument is ignored for this purpose. Here + is an example of pcre2test output, where the "mark" modifier requests the retrieval and outputting of (*MARK) data: re> /X(*MARK:A)Y|X(*MARK:B)Z/mark @@ -9311,76 +9350,76 @@ BACKTRACKING CONTROL MK: B The (*MARK) name is tagged with "MK:" in this output, and in this exam- - ple it indicates which of the two alternatives matched. This is a more - efficient way of obtaining this information than putting each alterna- + ple it indicates which of the two alternatives matched. This is a more + efficient way of obtaining this information than putting each alterna- tive in its own capturing parentheses. - If a verb with a name is encountered in a positive assertion that is - true, the name is recorded and passed back if it is the last-encoun- + If a verb with a name is encountered in a positive assertion that is + true, the name is recorded and passed back if it is the last-encoun- tered. This does not happen for negative assertions or failing positive assertions. - After a partial match or a failed match, the last encountered name in + After a partial match or a failed match, the last encountered name in the entire match process is returned. For example: re> /X(*MARK:A)Y|X(*MARK:B)Z/mark data> XP No match, mark = B - Note that in this unanchored example the mark is retained from the + Note that in this unanchored example the mark is retained from the match attempt that started at the letter "X" in the subject. Subsequent match attempts starting at "P" and then with an empty string do not get as far as the (*MARK) item, but nevertheless do not reset it. - If you are interested in (*MARK) values after failed matches, you - should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to + If you are interested in (*MARK) values after failed matches, you + should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to ensure that the match is always attempted. Verbs that act after backtracking The following verbs do nothing when they are encountered. Matching con- - tinues with what follows, but if there is a subsequent match failure, - causing a backtrack to the verb, a failure is forced. That is, back- - tracking cannot pass to the left of the verb. However, when one of + tinues with what follows, but if there is a subsequent match failure, + causing a backtrack to the verb, a failure is forced. That is, back- + tracking cannot pass to the left of the verb. However, when one of these verbs appears inside an atomic group or in a lookaround assertion - that is true, its effect is confined to that group, because once the - group has been matched, there is never any backtracking into it. Back- + that is true, its effect is confined to that group, because once the + group has been matched, there is never any backtracking into it. Back- tracking from beyond an assertion or an atomic group ignores the entire group, and seeks a preceding backtracking point. - These verbs differ in exactly what kind of failure occurs when back- - tracking reaches them. The behaviour described below is what happens - when the verb is not in a subroutine or an assertion. Subsequent sec- + These verbs differ in exactly what kind of failure occurs when back- + tracking reaches them. The behaviour described below is what happens + when the verb is not in a subroutine or an assertion. Subsequent sec- tions cover these special cases. (*COMMIT) or (*COMMIT:NAME) - This verb causes the whole match to fail outright if there is a later + This verb causes the whole match to fail outright if there is a later matching failure that causes backtracking to reach it. Even if the pat- - tern is unanchored, no further attempts to find a match by advancing - the starting point take place. If (*COMMIT) is the only backtracking + tern is unanchored, no further attempts to find a match by advancing + the starting point take place. If (*COMMIT) is the only backtracking verb that is encountered, once it has been passed pcre2_match() is com- mitted to finding a match at the current starting point, or not at all. For example: a+(*COMMIT)b - This matches "xxaab" but not "aacaab". It can be thought of as a kind + This matches "xxaab" but not "aacaab". It can be thought of as a kind of dynamic anchor, or "I've started, so I must finish." - The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM- - MIT). It is like (*MARK:NAME) in that the name is remembered for pass- - ing back to the caller. However, (*SKIP:NAME) searches only for names + The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM- + MIT). It is like (*MARK:NAME) in that the name is remembered for pass- + ing back to the caller. However, (*SKIP:NAME) searches only for names that are set with (*MARK), ignoring those set by any of the other back- tracking verbs. - If there is more than one backtracking verb in a pattern, a different - one that follows (*COMMIT) may be triggered first, so merely passing + If there is more than one backtracking verb in a pattern, a different + one that follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a match does not always guarantee that a match must be at this starting point. Note that (*COMMIT) at the start of a pattern is not the same as an an- - chor, unless PCRE2's start-of-match optimizations are turned off, as + chor, unless PCRE2's start-of-match optimizations are turned off, as shown in this output from pcre2test: re> /(*COMMIT)abc/ @@ -9391,68 +9430,68 @@ BACKTRACKING CONTROL data> xyzabc No match - For the first pattern, PCRE2 knows that any match must start with "a", - so the optimization skips along the subject to "a" before applying the - pattern to the first set of data. The match attempt then succeeds. The - second pattern disables the optimization that skips along to the first - character. The pattern is now applied starting at "x", and so the - (*COMMIT) causes the match to fail without trying any other starting + For the first pattern, PCRE2 knows that any match must start with "a", + so the optimization skips along the subject to "a" before applying the + pattern to the first set of data. The match attempt then succeeds. The + second pattern disables the optimization that skips along to the first + character. The pattern is now applied starting at "x", and so the + (*COMMIT) causes the match to fail without trying any other starting points. (*PRUNE) or (*PRUNE:NAME) - This verb causes the match to fail at the current starting position in + This verb causes the match to fail at the current starting position in the subject if there is a later matching failure that causes backtrack- - ing to reach it. If the pattern is unanchored, the normal "bumpalong" - advance to the next starting character then happens. Backtracking can - occur as usual to the left of (*PRUNE), before it is reached, or when - matching to the right of (*PRUNE), but if there is no match to the - right, backtracking cannot cross (*PRUNE). In simple cases, the use of - (*PRUNE) is just an alternative to an atomic group or possessive quan- + ing to reach it. If the pattern is unanchored, the normal "bumpalong" + advance to the next starting character then happens. Backtracking can + occur as usual to the left of (*PRUNE), before it is reached, or when + matching to the right of (*PRUNE), but if there is no match to the + right, backtracking cannot cross (*PRUNE). In simple cases, the use of + (*PRUNE) is just an alternative to an atomic group or possessive quan- tifier, but there are some uses of (*PRUNE) that cannot be expressed in - any other way. In an anchored pattern (*PRUNE) has the same effect as + any other way. In an anchored pattern (*PRUNE) has the same effect as (*COMMIT). The behaviour of (*PRUNE:NAME) is not the same as (*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is remembered for passing back - to the caller. However, (*SKIP:NAME) searches only for names set with + to the caller. However, (*SKIP:NAME) searches only for names set with (*MARK), ignoring those set by other backtracking verbs. (*SKIP) - This verb, when given without a name, is like (*PRUNE), except that if - the pattern is unanchored, the "bumpalong" advance is not to the next + This verb, when given without a name, is like (*PRUNE), except that if + the pattern is unanchored, the "bumpalong" advance is not to the next character, but to the position in the subject where (*SKIP) was encoun- - tered. (*SKIP) signifies that whatever text was matched leading up to - it cannot be part of a successful match if there is a later mismatch. + tered. (*SKIP) signifies that whatever text was matched leading up to + it cannot be part of a successful match if there is a later mismatch. Consider: a+(*SKIP)b - If the subject is "aaaac...", after the first match attempt fails - (starting at the first character in the string), the starting point + If the subject is "aaaac...", after the first match attempt fails + (starting at the first character in the string), the starting point skips on to start the next attempt at "c". Note that a possessive quan- tifier does not have the same effect as this example; although it would - suppress backtracking during the first match attempt, the second at- - tempt would start at the second character instead of skipping on to + suppress backtracking during the first match attempt, the second at- + tempt would start at the second character instead of skipping on to "c". - If (*SKIP) is used to specify a new starting position that is the same - as the starting position of the current match, or (by being inside a - lookbehind) earlier, the position specified by (*SKIP) is ignored, and + If (*SKIP) is used to specify a new starting position that is the same + as the starting position of the current match, or (by being inside a + lookbehind) earlier, the position specified by (*SKIP) is ignored, and instead the normal "bumpalong" occurs. (*SKIP:NAME) - When (*SKIP) has an associated name, its behaviour is modified. When - such a (*SKIP) is triggered, the previous path through the pattern is - searched for the most recent (*MARK) that has the same name. If one is - found, the "bumpalong" advance is to the subject position that corre- - sponds to that (*MARK) instead of to where (*SKIP) was encountered. If + When (*SKIP) has an associated name, its behaviour is modified. When + such a (*SKIP) is triggered, the previous path through the pattern is + searched for the most recent (*MARK) that has the same name. If one is + found, the "bumpalong" advance is to the subject position that corre- + sponds to that (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a matching name is found, the (*SKIP) is ignored. - The search for a (*MARK) name uses the normal backtracking mechanism, - which means that it does not see (*MARK) settings that are inside + The search for a (*MARK) name uses the normal backtracking mechanism, + which means that it does not see (*MARK) settings that are inside atomic groups or assertions, because they are never re-entered by back- tracking. Compare the following pcre2test examples: @@ -9466,105 +9505,105 @@ BACKTRACKING CONTROL 0: b 1: b - In the first example, the (*MARK) setting is in an atomic group, so it + In the first example, the (*MARK) setting is in an atomic group, so it is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. - This allows the second branch of the pattern to be tried at the first - character position. In the second example, the (*MARK) setting is not - in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it + This allows the second branch of the pattern to be tried at the first + character position. In the second example, the (*MARK) setting is not + in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new matching attempt to start at the sec- - ond character. This time, the (*MARK) is never seen because "a" does + ond character. This time, the (*MARK) is never seen because "a" does not match "b", so the matcher immediately jumps to the second branch of the pattern. - Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It + Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores names that are set by other backtracking verbs. (*THEN) or (*THEN:NAME) - This verb causes a skip to the next innermost alternative when back- - tracking reaches it. That is, it cancels any further backtracking - within the current alternative. Its name comes from the observation + This verb causes a skip to the next innermost alternative when back- + tracking reaches it. That is, it cancels any further backtracking + within the current alternative. Its name comes from the observation that it can be used for a pattern-based if-then-else block: ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ... - If the COND1 pattern matches, FOO is tried (and possibly further items - after the end of the group if FOO succeeds); on failure, the matcher - skips to the second alternative and tries COND2, without backtracking - into COND1. If that succeeds and BAR fails, COND3 is tried. If subse- - quently BAZ fails, there are no more alternatives, so there is a back- - track to whatever came before the entire group. If (*THEN) is not in- + If the COND1 pattern matches, FOO is tried (and possibly further items + after the end of the group if FOO succeeds); on failure, the matcher + skips to the second alternative and tries COND2, without backtracking + into COND1. If that succeeds and BAR fails, COND3 is tried. If subse- + quently BAZ fails, there are no more alternatives, so there is a back- + track to whatever came before the entire group. If (*THEN) is not in- side an alternation, it acts like (*PRUNE). - The behaviour of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN). + The behaviour of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is remembered for passing back - to the caller. However, (*SKIP:NAME) searches only for names set with + to the caller. However, (*SKIP:NAME) searches only for names set with (*MARK), ignoring those set by other backtracking verbs. - A group that does not contain a | character is just a part of the en- - closing alternative; it is not a nested alternation with only one al- + A group that does not contain a | character is just a part of the en- + closing alternative; it is not a nested alternation with only one al- ternative. The effect of (*THEN) extends beyond such a group to the en- - closing alternative. Consider this pattern, where A, B, etc. are com- - plex pattern fragments that do not contain any | characters at this + closing alternative. Consider this pattern, where A, B, etc. are com- + plex pattern fragments that do not contain any | characters at this level: A (B(*THEN)C) | D - If A and B are matched, but there is a failure in C, matching does not + If A and B are matched, but there is a failure in C, matching does not backtrack into A; instead it moves to the next alternative, that is, D. - However, if the group containing (*THEN) is given an alternative, it + However, if the group containing (*THEN) is given an alternative, it behaves differently: A (B(*THEN)C | (*FAIL)) | D The effect of (*THEN) is now confined to the inner group. After a fail- - ure in C, matching moves to (*FAIL), which causes the whole group to - fail because there are no more alternatives to try. In this case, + ure in C, matching moves to (*FAIL), which causes the whole group to + fail because there are no more alternatives to try. In this case, matching does backtrack into A. - Note that a conditional group is not considered as having two alterna- - tives, because only one is ever used. In other words, the | character - in a conditional group has a different meaning. Ignoring white space, + Note that a conditional group is not considered as having two alterna- + tives, because only one is ever used. In other words, the | character + in a conditional group has a different meaning. Ignoring white space, consider: ^.*? (?(?=a) a | b(*THEN)c ) If the subject is "ba", this pattern does not match. Because .*? is un- - greedy, it initially matches zero characters. The condition (?=a) then - fails, the character "b" is matched, but "c" is not. At this point, - matching does not backtrack to .*? as might perhaps be expected from - the presence of the | character. The conditional group is part of the - single alternative that comprises the whole pattern, and so the match - fails. (If there was a backtrack into .*?, allowing it to match "b", + greedy, it initially matches zero characters. The condition (?=a) then + fails, the character "b" is matched, but "c" is not. At this point, + matching does not backtrack to .*? as might perhaps be expected from + the presence of the | character. The conditional group is part of the + single alternative that comprises the whole pattern, and so the match + fails. (If there was a backtrack into .*?, allowing it to match "b", the match would succeed.) - The verbs just described provide four different "strengths" of control + The verbs just described provide four different "strengths" of control when subsequent matching fails. (*THEN) is the weakest, carrying on the - match at the next alternative. (*PRUNE) comes next, failing the match - at the current starting position, but allowing an advance to the next - character (for an unanchored pattern). (*SKIP) is similar, except that + match at the next alternative. (*PRUNE) comes next, failing the match + at the current starting position, but allowing an advance to the next + character (for an unanchored pattern). (*SKIP) is similar, except that the advance may be more than one character. (*COMMIT) is the strongest, causing the entire match to fail. More than one backtracking verb - If more than one backtracking verb is present in a pattern, the one - that is backtracked onto first acts. For example, consider this pat- + If more than one backtracking verb is present in a pattern, the one + that is backtracked onto first acts. For example, consider this pat- tern, where A, B, etc. are complex pattern fragments: (A(*COMMIT)B(*THEN)C|ABD) - If A matches but B fails, the backtrack to (*COMMIT) causes the entire + If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to fail. However, if A and B match, but C fails, the backtrack to - (*THEN) causes the next alternative (ABD) to be tried. This behaviour - is consistent, but is not always the same as Perl's. It means that if - two or more backtracking verbs appear in succession, all the the last + (*THEN) causes the next alternative (ABD) to be tried. This behaviour + is consistent, but is not always the same as Perl's. It means that if + two or more backtracking verbs appear in succession, all the the last of them has no effect. Consider this example: ...(*COMMIT)(*PRUNE)... If there is a matching failure to the right, backtracking onto (*PRUNE) - causes it to be triggered, and its action is taken. There can never be + causes it to be triggered, and its action is taken. There can never be a backtrack onto (*COMMIT). Backtracking verbs in repeated groups @@ -9574,50 +9613,50 @@ BACKTRACKING CONTROL /(a(*COMMIT)b)+ac/ - If the subject is "abac", Perl matches unless its optimizations are - disabled, but PCRE2 always fails because the (*COMMIT) in the second + If the subject is "abac", Perl matches unless its optimizations are + disabled, but PCRE2 always fails because the (*COMMIT) in the second repeat of the group acts. Backtracking verbs in assertions - (*FAIL) in any assertion has its normal effect: it forces an immediate - backtrack. The behaviour of the other backtracking verbs depends on - whether or not the assertion is standalone or acting as the condition + (*FAIL) in any assertion has its normal effect: it forces an immediate + backtrack. The behaviour of the other backtracking verbs depends on + whether or not the assertion is standalone or acting as the condition in a conditional group. - (*ACCEPT) in a standalone positive assertion causes the assertion to - succeed without any further processing; captured strings and a mark - name (if set) are retained. In a standalone negative assertion, (*AC- + (*ACCEPT) in a standalone positive assertion causes the assertion to + succeed without any further processing; captured strings and a mark + name (if set) are retained. In a standalone negative assertion, (*AC- CEPT) causes the assertion to fail without any further processing; cap- tured substrings and any mark name are discarded. - If the assertion is a condition, (*ACCEPT) causes the condition to be - true for a positive assertion and false for a negative one; captured + If the assertion is a condition, (*ACCEPT) causes the condition to be + true for a positive assertion and false for a negative one; captured substrings are retained in both cases. The remaining verbs act only when a later failure causes a backtrack to - reach them. This means that, for the Perl-compatible assertions, their + reach them. This means that, for the Perl-compatible assertions, their effect is confined to the assertion, because Perl lookaround assertions are atomic. A backtrack that occurs after such an assertion is complete - does not jump back into the assertion. Note in particular that a - (*MARK) name that is set in an assertion is not "seen" by an instance + does not jump back into the assertion. Note in particular that a + (*MARK) name that is set in an assertion is not "seen" by an instance of (*SKIP:NAME) later in the pattern. - PCRE2 now supports non-atomic positive assertions, as described in the - section entitled "Non-atomic assertions" above. These assertions must - be standalone (not used as conditions). They are not Perl-compatible. - For these assertions, a later backtrack does jump back into the asser- - tion, and therefore verbs such as (*COMMIT) can be triggered by back- + PCRE2 now supports non-atomic positive assertions, as described in the + section entitled "Non-atomic assertions" above. These assertions must + be standalone (not used as conditions). They are not Perl-compatible. + For these assertions, a later backtrack does jump back into the asser- + tion, and therefore verbs such as (*COMMIT) can be triggered by back- tracks from later in the pattern. - The effect of (*THEN) is not allowed to escape beyond an assertion. If - there are no more branches to try, (*THEN) causes a positive assertion + The effect of (*THEN) is not allowed to escape beyond an assertion. If + there are no more branches to try, (*THEN) causes a positive assertion to be false, and a negative assertion to be true. - The other backtracking verbs are not treated specially if they appear - in a standalone positive assertion. In a conditional positive asser- + The other backtracking verbs are not treated specially if they appear + in a standalone positive assertion. In a conditional positive asser- tion, backtracking (from within the assertion) into (*COMMIT), (*SKIP), - or (*PRUNE) causes the condition to be false. However, for both stand- + or (*PRUNE) causes the condition to be false. However, for both stand- alone and conditional negative assertions, backtracking into (*COMMIT), (*SKIP), or (*PRUNE) causes the assertion to be true, without consider- ing any further alternative branches. @@ -9627,26 +9666,26 @@ BACKTRACKING CONTROL These behaviours occur whether or not the group is called recursively. (*ACCEPT) in a group called as a subroutine causes the subroutine match - to succeed without any further processing. Matching then continues af- - ter the subroutine call. Perl documents this behaviour. Perl's treat- + to succeed without any further processing. Matching then continues af- + ter the subroutine call. Perl documents this behaviour. Perl's treat- ment of the other verbs in subroutines is different in some cases. - (*FAIL) in a group called as a subroutine has its normal effect: it + (*FAIL) in a group called as a subroutine has its normal effect: it forces an immediate backtrack. - (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail - when triggered by being backtracked to in a group called as a subrou- + (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail + when triggered by being backtracked to in a group called as a subrou- tine. There is then a backtrack at the outer level. (*THEN), when triggered, skips to the next alternative in the innermost - enclosing group that has alternatives (its normal behaviour). However, + enclosing group that has alternatives (its normal behaviour). However, if there is no such group within the subroutine's group, the subroutine match fails and there is a backtrack at the outer level. SEE ALSO - pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3), + pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3), pcre2(3). @@ -9659,7 +9698,7 @@ AUTHOR REVISION - Last updated: 01 December 2021 + Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ @@ -10698,6 +10737,38 @@ SCRIPT NAMES FOR \p AND \P Warang_Citi, Yezidi, Yi, Zanabazar_Square. +BIDI_PROPERTIES FOR \p AND \P + + \p{Bidi_Control} matches a Bidi control character + \p{Bidi_Class: } matches a character with the given class + + The recognized classes are: + + AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space + + CHARACTER CLASSES [...] positive character class @@ -11027,7 +11098,7 @@ AUTHOR REVISION - Last updated: 30 August 2021 + Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ @@ -11073,251 +11144,252 @@ UNICODE PROPERTY SUPPORT ting. The Unicode properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal number, the Unicode script names such as Arabic or Han, - and the derived properties Any and L&. Full lists are given in the - pcre2pattern and pcre2syntax documentation. Only the short names for - properties are supported. For example, \p{L} matches a letter. Its Perl - synonym, \p{Letter}, is not supported. Furthermore, in Perl, many - properties may optionally be prefixed by "Is", for compatibility with - Perl 5.6. PCRE2 does not support this. + Bidi_Class, Bidi_Control, and the derived properties Any and LC (syn- + onym L&). Full lists are given in the pcre2pattern and pcre2syntax doc- + umentation. Only the short names for properties are supported. For ex- + ample, \p{L} matches a letter. Its longer synonym, \p{Letter}, is not + supported. Furthermore, in Perl, many properties may optionally be + prefixed by "Is", for compatibility with Perl 5.6. PCRE2 does not sup- + port this. WIDE CHARACTERS AND UTF MODES Code points less than 256 can be specified in patterns by either braced or unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). - Larger values have to use braced sequences. Unbraced octal code points + Larger values have to use braced sequences. Unbraced octal code points up to \777 are also recognized; larger ones can be coded using \o{...}. - The escape sequence \N{U+ } is recognized as another way of - specifying a Unicode character by code point in a UTF mode. It is not + The escape sequence \N{U+ } is recognized as another way of + specifying a Unicode character by code point in a UTF mode. It is not allowed in non-UTF mode. - In UTF mode, repeat quantifiers apply to complete UTF characters, not + In UTF mode, repeat quantifiers apply to complete UTF characters, not to individual code units. In UTF mode, the dot metacharacter matches one UTF character instead of a single code unit. - In UTF mode, capture group names are not restricted to ASCII, and may + In UTF mode, capture group names are not restricted to ASCII, and may contain any Unicode letters and decimal digits, as well as underscore. - The escape sequence \C can be used to match a single code unit in UTF + The escape sequence \C can be used to match a single code unit in UTF mode, but its use can lead to some strange effects because it breaks up - multi-unit characters (see the description of \C in the pcre2pattern + multi-unit characters (see the description of \C in the pcre2pattern documentation). For this reason, there is a build-time option that dis- - ables support for \C completely. There is also a less draconian com- - pile-time option for locking out the use of \C when a pattern is com- + ables support for \C completely. There is also a less draconian com- + pile-time option for locking out the use of \C when a pattern is com- piled. - The use of \C is not supported by the alternative matching function + The use of \C is not supported by the alternative matching function pcre2_dfa_match() when in UTF-8 or UTF-16 mode, that is, when a charac- - ter may consist of more than one code unit. The use of \C in these - modes provokes a match-time error. Also, the JIT optimization does not + ter may consist of more than one code unit. The use of \C in these + modes provokes a match-time error. Also, the JIT optimization does not support \C in these modes. If JIT optimization is requested for a UTF-8 - or UTF-16 pattern that contains \C, it will not succeed, and so when + or UTF-16 pattern that contains \C, it will not succeed, and so when pcre2_match() is called, the matching will be carried out by the inter- pretive function. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly test - characters of any code value, but, by default, the characters that - PCRE2 recognizes as digits, spaces, or word characters remain the same - set as in non-UTF mode, all with code points less than 256. This re- + characters of any code value, but, by default, the characters that + PCRE2 recognizes as digits, spaces, or word characters remain the same + set as in non-UTF mode, all with code points less than 256. This re- mains true even when PCRE2 is built to include Unicode support, because - to do otherwise would slow down matching in many common cases. Note - that this also applies to \b and \B, because they are defined in terms - of \w and \W. If you want to test for a wider sense of, say, "digit", - you can use explicit Unicode property tests such as \p{Nd}. Alterna- + to do otherwise would slow down matching in many common cases. Note + that this also applies to \b and \B, because they are defined in terms + of \w and \W. If you want to test for a wider sense of, say, "digit", + you can use explicit Unicode property tests such as \p{Nd}. Alterna- tively, if you set the PCRE2_UCP option, the way that the character es- - capes work is changed so that Unicode properties are used to determine - which characters match. There are more details in the section on + capes work is changed so that Unicode properties are used to determine + which characters match. There are more details in the section on generic character types in the pcre2pattern documentation. - Similarly, characters that match the POSIX named character classes are + Similarly, characters that match the POSIX named character classes are all low-valued characters, unless the PCRE2_UCP option is set. - However, the special horizontal and vertical white space matching es- + However, the special horizontal and vertical white space matching es- capes (\h, \H, \v, and \V) do match all the appropriate Unicode charac- ters, whether or not PCRE2_UCP is set. UNICODE CASE-EQUIVALENCE - If either PCRE2_UTF or PCRE2_UCP is set, upper/lower case processing + If either PCRE2_UTF or PCRE2_UCP is set, upper/lower case processing makes use of Unicode properties except for characters whose code points are less than 128 and that have at most two case-equivalent values. For - these, a direct table lookup is used for speed. A few Unicode charac- - ters such as Greek sigma have more than two code points that are case- - equivalent, and these are treated specially. Setting PCRE2_UCP without - PCRE2_UTF allows Unicode-style case processing for non-UTF character + these, a direct table lookup is used for speed. A few Unicode charac- + ters such as Greek sigma have more than two code points that are case- + equivalent, and these are treated specially. Setting PCRE2_UCP without + PCRE2_UTF allows Unicode-style case processing for non-UTF character encodings such as UCS-2. SCRIPT RUNS - The pattern constructs (*script_run:...) and (*atomic_script_run:...), - with synonyms (*sr:...) and (*asr:...), verify that the string matched - within the parentheses is a script run. In concept, a script run is a - sequence of characters that are all from the same Unicode script. How- + The pattern constructs (*script_run:...) and (*atomic_script_run:...), + with synonyms (*sr:...) and (*asr:...), verify that the string matched + within the parentheses is a script run. In concept, a script run is a + sequence of characters that are all from the same Unicode script. How- ever, because some scripts are commonly used together, and because some - diacritical and other marks are used with multiple scripts, it is not + diacritical and other marks are used with multiple scripts, it is not that simple. Every Unicode character has a Script property, mostly with a value cor- - responding to the name of a script, such as Latin, Greek, or Cyrillic. + responding to the name of a script, such as Latin, Greek, or Cyrillic. There are also three special values: "Unknown" is used for code points that have not been assigned, and also - for the surrogate code points. In the PCRE2 32-bit library, characters - whose code points are greater than the Unicode maximum (U+10FFFF), - which are accessible only in non-UTF mode, are assigned the Unknown + for the surrogate code points. In the PCRE2 32-bit library, characters + whose code points are greater than the Unicode maximum (U+10FFFF), + which are accessible only in non-UTF mode, are assigned the Unknown script. - "Common" is used for characters that are used with many scripts. These - include punctuation, emoji, mathematical, musical, and currency sym- + "Common" is used for characters that are used with many scripts. These + include punctuation, emoji, mathematical, musical, and currency sym- bols, and the ASCII digits 0 to 9. - "Inherited" is used for characters such as diacritical marks that mod- + "Inherited" is used for characters such as diacritical marks that mod- ify a previous character. These are considered to take on the script of the character that they modify. - Some Inherited characters are used with many scripts, but many of them - are only normally used with a small number of scripts. For example, + Some Inherited characters are used with many scripts, but many of them + are only normally used with a small number of scripts. For example, U+102E0 (Coptic Epact thousands mark) is used only with Arabic and Cop- - tic. In order to make it possible to check this, a Unicode property + tic. In order to make it possible to check this, a Unicode property called Script Extension exists. Its value is a list of scripts that ap- ply to the character. For the majority of characters, the list contains - just one script, the same one as the Script property. However, for - characters such as U+102E0 more than one Script is listed. There are - also some Common characters that have a single, non-Common script in + just one script, the same one as the Script property. However, for + characters such as U+102E0 more than one Script is listed. There are + also some Common characters that have a single, non-Common script in their Script Extension list. The next section describes the basic rules for deciding whether a given - string of characters is a script run. Note, however, that there are - some special cases involving the Chinese Han script, and an additional - constraint for decimal digits. These are covered in subsequent sec- + string of characters is a script run. Note, however, that there are + some special cases involving the Chinese Han script, and an additional + constraint for decimal digits. These are covered in subsequent sec- tions. Basic script run rules A string that is less than two characters long is a script run. This is - the only case in which an Unknown character can be part of a script - run. Longer strings are checked using only the Script Extensions prop- + the only case in which an Unknown character can be part of a script + run. Longer strings are checked using only the Script Extensions prop- erty, not the basic Script property. - If a character's Script Extension property is the single value "Inher- + If a character's Script Extension property is the single value "Inher- ited", it is always accepted as part of a script run. This is also true - for the property "Common", subject to the checking of decimal digits + for the property "Common", subject to the checking of decimal digits described below. All the remaining characters in a script run must have - at least one script in common in their Script Extension lists. In set- + at least one script in common in their Script Extension lists. In set- theoretic terminology, the intersection of all the sets of scripts must not be empty. - A simple example is an Internet name such as "google.com". The letters + A simple example is an Internet name such as "google.com". The letters are all in the Latin script, and the dot is Common, so this string is a script run. However, the Cyrillic letter "o" looks exactly the same as - the Latin "o"; a string that looks the same, but with Cyrillic "o"s is + the Latin "o"; a string that looks the same, but with Cyrillic "o"s is not a script run. - More interesting examples involve characters with more than one script + More interesting examples involve characters with more than one script in their Script Extension. Consider the following characters: U+060C Arabic comma U+06D4 Arabic full stop - The first has the Script Extension list Arabic, Hanifi Rohingya, Syr- - iac, and Thaana; the second has just Arabic and Hanifi Rohingya. Both - of them could appear in script runs of either Arabic or Hanifi Ro- - hingya. The first could also appear in Syriac or Thaana script runs, + The first has the Script Extension list Arabic, Hanifi Rohingya, Syr- + iac, and Thaana; the second has just Arabic and Hanifi Rohingya. Both + of them could appear in script runs of either Arabic or Hanifi Ro- + hingya. The first could also appear in Syriac or Thaana script runs, but the second could not. The Chinese Han script - The Chinese Han script is commonly used in conjunction with other - scripts for writing certain languages. Japanese uses the Hiragana and - Katakana scripts together with Han; Korean uses Hangul and Han; Tai- - wanese Mandarin uses Bopomofo and Han. These three combinations are - treated as special cases when checking script runs and are, in effect, - "virtual scripts". Thus, a script run may contain a mixture of Hira- - gana, Katakana, and Han, or a mixture of Hangul and Han, or a mixture - of Bopomofo and Han, but not, for example, a mixture of Hangul and - Bopomofo and Han. PCRE2 (like Perl) follows Unicode's Technical Stan- - dard 39 ("Unicode Security Mechanisms", http://unicode.org/re- + The Chinese Han script is commonly used in conjunction with other + scripts for writing certain languages. Japanese uses the Hiragana and + Katakana scripts together with Han; Korean uses Hangul and Han; Tai- + wanese Mandarin uses Bopomofo and Han. These three combinations are + treated as special cases when checking script runs and are, in effect, + "virtual scripts". Thus, a script run may contain a mixture of Hira- + gana, Katakana, and Han, or a mixture of Hangul and Han, or a mixture + of Bopomofo and Han, but not, for example, a mixture of Hangul and + Bopomofo and Han. PCRE2 (like Perl) follows Unicode's Technical Stan- + dard 39 ("Unicode Security Mechanisms", http://unicode.org/re- ports/tr39/) in allowing such mixtures. Decimal digits - Unicode contains many sets of 10 decimal digits in different scripts, - and some scripts (including the Common script) contain more than one - set. Some of these decimal digits them are visually indistinguishable - from the common ASCII digits. In addition to the script checking de- - scribed above, if a script run contains any decimal digits, they must + Unicode contains many sets of 10 decimal digits in different scripts, + and some scripts (including the Common script) contain more than one + set. Some of these decimal digits them are visually indistinguishable + from the common ASCII digits. In addition to the script checking de- + scribed above, if a script run contains any decimal digits, they must all come from the same set of 10 adjacent characters. VALIDITY OF UTF STRINGS - When the PCRE2_UTF option is set, the strings passed as patterns and + When the PCRE2_UTF option is set, the strings passed as patterns and subjects are (by default) checked for validity on entry to the relevant functions. If an invalid UTF string is passed, a negative error code is - returned. The code unit offset to the offending character can be ex- - tracted from the match data block by calling pcre2_get_startchar(), + returned. The code unit offset to the offending character can be ex- + tracted from the match data block by calling pcre2_get_startchar(), which is used for this purpose after a UTF error. - In some situations, you may already know that your strings are valid, - and therefore want to skip these checks in order to improve perfor- - mance, for example in the case of a long subject string that is being - scanned repeatedly. If you set the PCRE2_NO_UTF_CHECK option at com- - pile time or at match time, PCRE2 assumes that the pattern or subject + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance, for example in the case of a long subject string that is being + scanned repeatedly. If you set the PCRE2_NO_UTF_CHECK option at com- + pile time or at match time, PCRE2 assumes that the pattern or subject it is given (respectively) contains only valid UTF code unit sequences. - If you pass an invalid UTF string when PCRE2_NO_UTF_CHECK is set, the - result is undefined and your program may crash or loop indefinitely or - give incorrect results. There is, however, one mode of matching that - can handle invalid UTF subject strings. This is enabled by passing - PCRE2_MATCH_INVALID_UTF to pcre2_compile() and is discussed below in - the next section. The rest of this section covers the case when + If you pass an invalid UTF string when PCRE2_NO_UTF_CHECK is set, the + result is undefined and your program may crash or loop indefinitely or + give incorrect results. There is, however, one mode of matching that + can handle invalid UTF subject strings. This is enabled by passing + PCRE2_MATCH_INVALID_UTF to pcre2_compile() and is discussed below in + the next section. The rest of this section covers the case when PCRE2_MATCH_INVALID_UTF is not set. - Passing PCRE2_NO_UTF_CHECK to pcre2_compile() just disables the UTF - check for the pattern; it does not also apply to subject strings. If - you want to disable the check for a subject string you must pass this + Passing PCRE2_NO_UTF_CHECK to pcre2_compile() just disables the UTF + check for the pattern; it does not also apply to subject strings. If + you want to disable the check for a subject string you must pass this same option to pcre2_match() or pcre2_dfa_match(). UTF-16 and UTF-32 strings can indicate their endianness by special code - knows as a byte-order mark (BOM). The PCRE2 functions do not handle + knows as a byte-order mark (BOM). The PCRE2 functions do not handle this, expecting strings to be in host byte order. - Unless PCRE2_NO_UTF_CHECK is set, a UTF string is checked before any + Unless PCRE2_NO_UTF_CHECK is set, a UTF string is checked before any other processing takes place. In the case of pcre2_match() and - pcre2_dfa_match() calls with a non-zero starting offset, the check is + pcre2_dfa_match() calls with a non-zero starting offset, the check is applied only to that part of the subject that could be inspected during - matching, and there is a check that the starting offset points to the - first code unit of a character or to the end of the subject. If there - are no lookbehind assertions in the pattern, the check starts at the - starting offset. Otherwise, it starts at the length of the longest - lookbehind before the starting offset, or at the start of the subject - if there are not that many characters before the starting offset. Note + matching, and there is a check that the starting offset points to the + first code unit of a character or to the end of the subject. If there + are no lookbehind assertions in the pattern, the check starts at the + starting offset. Otherwise, it starts at the length of the longest + lookbehind before the starting offset, or at the start of the subject + if there are not that many characters before the starting offset. Note that the sequences \b and \B are one-character lookbehinds. - In addition to checking the format of the string, there is a check to + In addition to checking the format of the string, there is a check to ensure that all code points lie in the range U+0 to U+10FFFF, excluding - the surrogate area. The so-called "non-character" code points are not + the surrogate area. The so-called "non-character" code points are not excluded because Unicode corrigendum #9 makes it clear that they should not be. - Characters in the "Surrogate Area" of Unicode are reserved for use by - UTF-16, where they are used in pairs to encode code points with values - greater than 0xFFFF. The code points that are encoded by UTF-16 pairs - are available independently in the UTF-8 and UTF-32 encodings. (In - other words, the whole surrogate thing is a fudge for UTF-16 which un- + Characters in the "Surrogate Area" of Unicode are reserved for use by + UTF-16, where they are used in pairs to encode code points with values + greater than 0xFFFF. The code points that are encoded by UTF-16 pairs + are available independently in the UTF-8 and UTF-32 encodings. (In + other words, the whole surrogate thing is a fudge for UTF-16 which un- fortunately messes up UTF-8 and UTF-32.) - Setting PCRE2_NO_UTF_CHECK at compile time does not disable the error - that is given if an escape sequence for an invalid Unicode code point - is encountered in the pattern. If you want to allow escape sequences - such as \x{d800} (a surrogate code point) you can set the PCRE2_EX- - TRA_ALLOW_SURROGATE_ESCAPES extra option. However, this is possible - only in UTF-8 and UTF-32 modes, because these values are not repre- + Setting PCRE2_NO_UTF_CHECK at compile time does not disable the error + that is given if an escape sequence for an invalid Unicode code point + is encountered in the pattern. If you want to allow escape sequences + such as \x{d800} (a surrogate code point) you can set the PCRE2_EX- + TRA_ALLOW_SURROGATE_ESCAPES extra option. However, this is possible + only in UTF-8 and UTF-32 modes, because these values are not repre- sentable in UTF-16. Errors in UTF-8 strings @@ -11330,10 +11402,10 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR4 PCRE2_ERROR_UTF8_ERR5 - The string ends with a truncated UTF-8 character; the code specifies - how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 - characters to be no longer than 4 bytes, the encoding scheme (origi- - nally defined by RFC 2279) allows for up to 6 bytes, and this is + The string ends with a truncated UTF-8 character; the code specifies + how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 + characters to be no longer than 4 bytes, the encoding scheme (origi- + nally defined by RFC 2279) allows for up to 6 bytes, and this is checked first; hence the possibility of 4 or 5 missing bytes. PCRE2_ERROR_UTF8_ERR6 @@ -11343,13 +11415,13 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR10 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of - the character do not have the binary value 0b10 (that is, either the + the character do not have the binary value 0b10 (that is, either the most significant bit is 0, or the next bit is 1). PCRE2_ERROR_UTF8_ERR11 PCRE2_ERROR_UTF8_ERR12 - A character that is valid by the RFC 2279 rules is either 5 or 6 bytes + A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code points are excluded by RFC 3629. PCRE2_ERROR_UTF8_ERR13 @@ -11359,8 +11431,8 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR14 - A 3-byte character has a value in the range 0xd800 to 0xdfff; this - range of code points are reserved by RFC 3629 for use with UTF-16, and + A 3-byte character has a value in the range 0xd800 to 0xdfff; this + range of code points are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8. PCRE2_ERROR_UTF8_ERR15 @@ -11369,26 +11441,26 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR18 PCRE2_ERROR_UTF8_ERR19 - A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes - for a value that can be represented by fewer bytes, which is invalid. - For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- + A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes + for a value that can be represented by fewer bytes, which is invalid. + For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- rect coding uses just one byte. PCRE2_ERROR_UTF8_ERR20 The two most significant bits of the first byte of a character have the - binary value 0b10 (that is, the most significant bit is 1 and the sec- - ond is 0). Such a byte can only validly occur as the second or subse- + binary value 0b10 (that is, the most significant bit is 1 and the sec- + ond is 0). Such a byte can only validly occur as the second or subse- quent byte of a multi-byte character. PCRE2_ERROR_UTF8_ERR21 - The first byte of a character has the value 0xfe or 0xff. These values + The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string. Errors in UTF-16 strings - The following negative error codes are given for invalid UTF-16 + The following negative error codes are given for invalid UTF-16 strings: PCRE2_ERROR_UTF16_ERR1 Missing low surrogate at end of string @@ -11398,7 +11470,7 @@ VALIDITY OF UTF STRINGS Errors in UTF-32 strings - The following negative error codes are given for invalid UTF-32 + The following negative error codes are given for invalid UTF-32 strings: PCRE2_ERROR_UTF32_ERR1 Surrogate character (0xd800 to 0xdfff) @@ -11408,47 +11480,47 @@ VALIDITY OF UTF STRINGS MATCHING IN INVALID UTF STRINGS You can run pattern matches on subject strings that may contain invalid - UTF sequences if you call pcre2_compile() with the PCRE2_MATCH_IN- - VALID_UTF option. This is supported by pcre2_match(), including JIT + UTF sequences if you call pcre2_compile() with the PCRE2_MATCH_IN- + VALID_UTF option. This is supported by pcre2_match(), including JIT matching, but not by pcre2_dfa_match(). When PCRE2_MATCH_INVALID_UTF is - set, it forces PCRE2_UTF to be set as well. Note, however, that the + set, it forces PCRE2_UTF to be set as well. Note, however, that the pattern itself must be a valid UTF string. - Setting PCRE2_MATCH_INVALID_UTF does not affect what pcre2_compile() - generates, but if pcre2_jit_compile() is subsequently called, it does + Setting PCRE2_MATCH_INVALID_UTF does not affect what pcre2_compile() + generates, but if pcre2_jit_compile() is subsequently called, it does generate different code. If JIT is not used, the option affects the be- haviour of the interpretive code in pcre2_match(). When PCRE2_MATCH_IN- - VALID_UTF is set at compile time, PCRE2_NO_UTF_CHECK is ignored at + VALID_UTF is set at compile time, PCRE2_NO_UTF_CHECK is ignored at match time. - In this mode, an invalid code unit sequence in the subject never - matches any pattern item. It does not match dot, it does not match - \p{Any}, it does not even match negative items such as [^X]. A lookbe- - hind assertion fails if it encounters an invalid sequence while moving - the current point backwards. In other words, an invalid UTF code unit + In this mode, an invalid code unit sequence in the subject never + matches any pattern item. It does not match dot, it does not match + \p{Any}, it does not even match negative items such as [^X]. A lookbe- + hind assertion fails if it encounters an invalid sequence while moving + the current point backwards. In other words, an invalid UTF code unit sequence acts as a barrier which no match can cross. You can also think of this as the subject being split up into fragments - of valid UTF, delimited internally by invalid code unit sequences. The - pattern is matched fragment by fragment. The result of a successful - match, however, is given as code unit offsets in the entire subject + of valid UTF, delimited internally by invalid code unit sequences. The + pattern is matched fragment by fragment. The result of a successful + match, however, is given as code unit offsets in the entire subject string in the usual way. There are a few points to consider: - The internal boundaries are not interpreted as the beginnings or ends - of lines and so do not match circumflex or dollar characters in the + The internal boundaries are not interpreted as the beginnings or ends + of lines and so do not match circumflex or dollar characters in the pattern. - If pcre2_match() is called with an offset that points to an invalid - UTF-sequence, that sequence is skipped, and the match starts at the + If pcre2_match() is called with an offset that points to an invalid + UTF-sequence, that sequence is skipped, and the match starts at the next valid UTF character, or the end of the subject. At internal fragment boundaries, \b and \B behave in the same way as at - the beginning and end of the subject. For example, a sequence such as - \bWORD\b would match an instance of WORD that is surrounded by invalid + the beginning and end of the subject. For example, a sequence such as + \bWORD\b would match an instance of WORD that is surrounded by invalid UTF code units. - Using PCRE2_MATCH_INVALID_UTF, an application can run matches on arbi- - trary data, knowing that any matched strings that are returned are + Using PCRE2_MATCH_INVALID_UTF, an application can run matches on arbi- + trary data, knowing that any matched strings that are returned are valid UTF. This can be useful when searching for UTF text in executable or other binary files. @@ -11462,8 +11534,8 @@ AUTHOR REVISION - Last updated: 23 February 2020 - Copyright (c) 1997-2020 University of Cambridge. + Last updated: 08 December 2021 + Copyright (c) 1997-2021 University of Cambridge. ------------------------------------------------------------------------------ diff --git a/doc/pcre2api.3 b/doc/pcre2api.3 index 30964db..47d4d07 100644 --- a/doc/pcre2api.3 +++ b/doc/pcre2api.3 @@ -1,4 +1,4 @@ -.TH PCRE2API 3 "30 November 2021" "PCRE2 10.40" +.TH PCRE2API 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE2 - Perl-compatible regular expressions (revised API) .sp @@ -2015,8 +2015,8 @@ point. However, this applies only to characters whose code points are less than 256. By default, higher-valued code points never match escapes such as \ew or \ed. .P -When PCRE2 is built with Unicode support (the default), the Unicode properties -of all characters can be tested with \ep and \eP, or, alternatively, the +When PCRE2 is built with Unicode support (the default), certain Unicode +character properties can be tested with \ep and \eP, or, alternatively, the PCRE2_UCP option can be set when a pattern is compiled; this causes \ew and friends to use Unicode property support instead of the built-in tables. PCRE2_UCP also causes upper/lower casing operations on characters with code @@ -4025,6 +4025,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 30 November 2021 +Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. .fi diff --git a/doc/pcre2build.3 b/doc/pcre2build.3 index 60931bf..c251dbf 100644 --- a/doc/pcre2build.3 +++ b/doc/pcre2build.3 @@ -1,4 +1,4 @@ -.TH PCRE2BUILD 3 "20 March 2020" "PCRE2 10.35" +.TH PCRE2BUILD 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE2 - Perl-compatible regular expressions (revised API) . @@ -122,8 +122,9 @@ locked this out by setting PCRE2_NEVER_UTF. UTF support allows the libraries to process character code points up to 0x10ffff in the strings that they handle. Unicode support also gives access to the Unicode properties of characters, using pattern escapes such as \eP, \ep, -and \eX. Only the general category properties such as \fILu\fP and \fINd\fP are -supported. Details are given in the +and \eX. Only the general category properties such as \fILu\fP and \fINd\fP, +script names, and some bi-directional properties are supported. Details are +given in the .\" HREF \fBpcre2pattern\fP .\" @@ -633,6 +634,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 20 March 2020 -Copyright (c) 1997-2020 University of Cambridge. +Last updated: 08 December 2021 +Copyright (c) 1997-2021 University of Cambridge. .fi diff --git a/doc/pcre2compat.3 b/doc/pcre2compat.3 index c463034..8333d3e 100644 --- a/doc/pcre2compat.3 +++ b/doc/pcre2compat.3 @@ -1,4 +1,4 @@ -.TH PCRE2COMPAT 3 "01 December 2021" "PCRE2 10.40" +.TH PCRE2COMPAT 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE2 - Perl-compatible regular expressions (revised API) .SH "DIFFERENCES BETWEEN PCRE2 AND PERL" @@ -50,9 +50,9 @@ interprets them. 6. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE2 is built with Unicode support (the default). The properties that can be tested with \ep and \eP are limited to the general category properties such as Lu and -Nd, script names such as Greek or Han, and the derived properties Any and L&. -Both PCRE2 and Perl support the Cs (surrogate) property, but in PCRE2 its use -is limited. See the +Nd, script names such as Greek or Han, Bidi_Class, Bidi_Control, and the +derived properties Any and LC (synonym L&). Both PCRE2 and Perl support the Cs +(surrogate) property, but in PCRE2 its use is limited. See the .\" HREF \fBpcre2pattern\fP .\" @@ -222,6 +222,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 01 December 2021 +Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. .fi diff --git a/doc/pcre2pattern.3 b/doc/pcre2pattern.3 index 87c7252..eb9bb0f 100644 --- a/doc/pcre2pattern.3 +++ b/doc/pcre2pattern.3 @@ -1,4 +1,4 @@ -.TH PCRE2PATTERN 3 "01 December 2021" "PCRE2 10.40" +.TH PCRE2PATTERN 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE2 - Perl-compatible regular expressions (revised API) .SH "PCRE2 REGULAR EXPRESSION DETAILS" @@ -779,13 +779,15 @@ escape sequences are: \eP{\fIxx\fP} a character without the \fIxx\fP property \eX a Unicode extended grapheme cluster .sp -The property names represented by \fIxx\fP above are case-sensitive. There is -support for Unicode script names, Unicode general category properties, "Any", -which matches any character (including newline), and some special PCRE2 -properties (described in the +The property names represented by \fIxx\fP above are not case-sensitive, and in +accordance with Unicode's "loose matching" rules, spaces, hyphens, and +underscores are ignored. There is support for Unicode script names, Unicode +general category properties, "Any", which matches any character (including +newline), Bidi_Control, Bidi_Class, and some special PCRE2 properties +(described .\" HTML .\" -next section). +below). .\" Other Perl properties such as "InMusicalSymbols" are not supported by PCRE2. Note that \eP{Any} does not match any characters, so always causes a match @@ -1025,9 +1027,9 @@ The following general category property codes are supported: Zp Paragraph separator Zs Space separator .sp -The special property L& is also supported: it matches a character that has -the Lu, Ll, or Lt property, in other words, a letter that is not classified as -a modifier or "other". +The special property LC, which has the synonym L&, is also supported: it +matches a character that has the Lu, Ll, or Lt property, in other words, a +letter that is not classified as a modifier or "other". .P The Cs (Surrogate) property applies only to characters whose code points are in the range U+D800 to U+DFFF. These characters are no different to any other @@ -1059,6 +1061,45 @@ properties in PCRE2 by default, though you can make them do so by setting the PCRE2_UCP option or by starting the pattern with (*UCP). . . +.SS "Bi-directional properties for \ep and \eP" +.rs +.sp +Two properties relating to bi-directional text are supported: +.sp + \ep{Bidi_Control} matches a Bidi control character + \ep{Bidi_Class: } matches a character with the given class +.sp +The recognized classes are: +.sp + AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space +.sp +For Bidi_Class, an equals sign may be used instead of a colon. The class names +are case-insensitive. As for other properties, only the short names are +recognized. +. +. .SS Extended grapheme clusters .rs .sp @@ -3909,6 +3950,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 01 December 2021 +Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. .fi diff --git a/doc/pcre2syntax.3 b/doc/pcre2syntax.3 index 937c817..4478857 100644 --- a/doc/pcre2syntax.3 +++ b/doc/pcre2syntax.3 @@ -1,4 +1,4 @@ -.TH PCRE2SYNTAX 3 "30 August 2021" "PCRE2 10.38" +.TH PCRE2SYNTAX 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE2 - Perl-compatible regular expressions (revised API) .SH "PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY" @@ -333,6 +333,39 @@ Yi, Zanabazar_Square. . . +.SH "BIDI_PROPERTIES FOR \ep AND \eP" +.rs +.sp + \ep{Bidi_Control} matches a Bidi control character + \ep{Bidi_Class: } matches a character with the given class +.sp +The recognized classes are: +.sp + AL Arabic letter + AN Arabic number + B paragraph separator + BN boundary neutral + CS common separator + EN European number + ES European separator + ET European terminator + FSI first strong isolate + L left-to-right + LRE left-to-right embedding + LRI left-to-right isolate + LRO left-to-right override + NSM non-spacing mark + ON other neutral + PDF pop directional format + PDI pop directional isolate + R right-to-left + RLE right-to-left embedding + RLI right-to-left isolate + RLO right-to-left override + S segment separator + WS which space +. +. .SH "CHARACTER CLASSES" .rs .sp @@ -684,6 +717,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 30 August 2021 +Last updated: 08 December 2021 Copyright (c) 1997-2021 University of Cambridge. .fi diff --git a/doc/pcre2unicode.3 b/doc/pcre2unicode.3 index 055a4ce..12db95e 100644 --- a/doc/pcre2unicode.3 +++ b/doc/pcre2unicode.3 @@ -1,4 +1,4 @@ -.TH PCRE2UNICODE 3 "23 February 2020" "PCRE2 10.35" +.TH PCRE2UNICODE 3 "08 December 2021" "PCRE2 10.40" .SH NAME PCRE - Perl-compatible regular expressions (revised API) .SH "UNICODE AND UTF SUPPORT" @@ -42,8 +42,8 @@ When PCRE2 is built with Unicode support, the escape sequences \ep{..}, \eP{..}, and \eX can be used. This is not dependent on the PCRE2_UTF setting. The Unicode properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal number, the -Unicode script names such as Arabic or Han, and the derived properties Any and -L&. Full lists are given in the +Unicode script names such as Arabic or Han, Bidi_Class, Bidi_Control, and the +derived properties Any and LC (synonym L&). Full lists are given in the .\" HREF \fBpcre2pattern\fP .\" @@ -52,7 +52,7 @@ and \fBpcre2syntax\fP .\" documentation. Only the short names for properties are supported. For example, -\ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported. +\ep{L} matches a letter. Its longer synonym, \ep{Letter}, is not supported. Furthermore, in Perl, many properties may optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE2 does not support this. . @@ -457,6 +457,6 @@ Cambridge, England. .rs .sp .nf -Last updated: 23 February 2020 -Copyright (c) 1997-2020 University of Cambridge. +Last updated: 08 December 2021 +Copyright (c) 1997-2021 University of Cambridge. .fi