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73
doc/html/pcre2compat.html
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@ -18,33 +18,41 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
<P>
This document describes some of the differences in the ways that PCRE2 and Perl
handle regular expressions. The differences described here are with respect to
Perl version 5.32.0, but as both Perl and PCRE2 are continually changing, the
Perl version 5.34.0, but as both Perl and PCRE2 are continually changing, the
information may at times be out of date.
</P>
<P>
1. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
1. When PCRE2_DOTALL (equivalent to Perl's /s qualifier) is not set, the
behaviour of the '.' metacharacter differs from Perl. In PCRE2, '.' matches the
next character unless it is the start of a newline sequence. This means that,
if the newline setting is CR, CRLF, or NUL, '.' will match the code point LF
(0x0A) in ASCII/Unicode environments, and NL (either 0x15 or 0x25) when using
EBCDIC. In Perl, '.' appears never to match LF, even when 0x0A is not a newline
indicator.
</P>
<P>
2. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
have are given in the
<a href="pcre2unicode.html"><b>pcre2unicode</b></a>
page.
</P>
<P>
2. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
3. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
they do not mean what you might think. For example, (?!a){3} does not assert
that the next three characters are not "a". It just asserts that the next
character is not "a" three times (in principle; PCRE2 optimizes this to run the
assertion just once). Perl allows some repeat quantifiers on other assertions,
for example, \b* (but not \b{3}, though oddly it does allow ^{3}), but these
do not seem to have any use. PCRE2 does not allow any kind of quantifier on
non-lookaround assertions.
for example, \b* , but these do not seem to have any use. PCRE2 does not allow
any kind of quantifier on non-lookaround assertions.
</P>
<P>
3. Capture groups that occur inside negative lookaround assertions are counted,
4. Capture groups that occur inside negative lookaround assertions are counted,
but their entries in the offsets vector are set only when a negative assertion
is a condition that has a matching branch (that is, the condition is false).
Perl may set such capture groups in other circumstances.
</P>
<P>
4. The following Perl escape sequences are not supported: \F, \l, \L, \u,
5. The following Perl escape sequences are not supported: \F, \l, \L, \u,
\U, and \N when followed by a character name. \N on its own, matching a
non-newline character, and \N{U+dd..}, matching a Unicode code point, are
supported. The escapes that modify the case of following letters are
@ -55,7 +63,7 @@ PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are interpreted as ECMAScript
interprets them.
</P>
<P>
5. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is
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&.
@ -67,14 +75,14 @@ supports (such as \p{Letter}) are not supported by PCRE2, nor is it permitted
to prefix any of these properties with "Is".
</P>
<P>
6. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
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 quotes. In Perl,
they cause variable interpolation (but of course 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 just like any
other character. Note the following examples:
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 just like any other character. Note the
following examples:
<pre>
Pattern PCRE2 matches Perl matches
@ -88,19 +96,19 @@ The \Q...\E sequence is recognized both inside and outside character classes
by both PCRE2 and Perl.
</P>
<P>
7. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code})
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
<a href="pcre2callout.html"><b>pcre2callout</b></a>
documentation for details.
</P>
<P>
8. Subroutine calls (whether recursive or not) were treated as atomic groups up
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.
</P>
<P>
9. In PCRE2, if any of the backtracking control verbs are used in a group that
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 surrounding pattern. This is
not always the case in Perl. In particular, if (*THEN) is present in a group
@ -109,20 +117,20 @@ the group does not contain any | characters. Note that such groups are
processed as anchored at the point where they are tested.
</P>
<P>
10. If a pattern contains more than one backtracking control verb, the first
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.
</P>
<P>
11. There are some differences that are concerned with the settings of captured
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 unset, but in PCRE2 it is set to
"b".
</P>
<P>
12. PCRE2's handling of duplicate capture group numbers and names is not as
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 translate between numbers and
names. In particular, a pattern such as (?|(?&#60;a&#62;A)|(?&#60;b&#62;B)), where the two
@ -132,42 +140,43 @@ to distinguish which group matched, because both names map to capture group
number 1. To avoid this confusing situation, an error is given at compile time.
</P>
<P>
13. Perl used to recognize comments in some places that PCRE2 does not, for
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 may still be some cases where
Perl behaves differently.
</P>
<P>
14. Perl, when in warning mode, gives warnings for character classes such as
15. Perl, when in warning mode, gives warnings for character classes such as
[A-\d] or [a-[:digit:]]. It then treats the hyphens as literals. PCRE2 has no
warning features, so it gives an error in these cases because they are almost
certainly user mistakes.
</P>
<P>
15. In PCRE2, the upper/lower case character properties Lu and Ll are not
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 (5.32), \p{Lu} and \p{Ll} match all
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.
</P>
<P>
16. From release 5.32.0, Perl locks out the use of \K in lookaround
17. From release 5.32.0, Perl locks out the use of \K in lookaround
assertions. 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.
</P>
<P>
17. PCRE2 provides some extensions to the Perl regular expression facilities.
18. PCRE2 provides some extensions to the Perl regular expression facilities.
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 5.32:
list is with respect to Perl 5.34:
<br>
<br>
(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 requires them all to have the same length.
different length of string. Perl used to require them all to have the same
length, but the latest version has some variable length support.
<br>
<br>
(b) From PCRE2 10.23, backreferences to groups of fixed length are supported
@ -221,12 +230,12 @@ extension to the lookaround facilities. The default, Perl-compatible
lookarounds are atomic.
</P>
<P>
18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
19. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
modifier restricts /i case-insensitive matching to pure ascii, ignoring Unicode
rules. This separation cannot be represented with PCRE2_UCP.
</P>
<P>
19. Perl has different limits than PCRE2. See the
20. Perl has different limits than PCRE2. See the
<a href="pcre2limit.html"><b>pcre2limit</b></a>
documentation for details. Perl went with 5.10 from recursion to iteration
keeping the intermediate matches on the heap, which is ~10% slower but does not
@ -248,7 +257,7 @@ Cambridge, England.
REVISION
</b><br>
<P>
Last updated: 30 August 2021
Last updated: 01 December 2021
<br>
Copyright &copy; 1997-2021 University of Cambridge.
<br>

18
doc/html/pcre2pattern.html
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@ -1341,15 +1341,17 @@ end of the subject in both modes, and if all branches of a pattern start with
<P>
Outside a character class, a dot in the pattern matches any one character in
the subject string except (by default) a character that signifies the end of a
line.
line. One or more characters may be specified as line terminators (see
<a href="#newlines">"Newline conventions"</a>
above).
</P>
<P>
When a line ending is defined as a single character, dot never matches that
character; when the two-character sequence CRLF is used, dot does not match CR
if it is immediately followed by LF, but otherwise it matches all characters
(including isolated CRs and LFs). When any Unicode line endings are being
recognized, dot does not match CR or LF or any of the other line ending
characters.
Dot never matches a single line-ending character. When the two-character
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.
</P>
<P>
The behaviour of dot with regard to newlines can be changed. If the
@ -3859,7 +3861,7 @@ Cambridge, England.
</P>
<br><a name="SEC32" href="#TOC1">REVISION</a><br>
<P>
Last updated: 30 August 2021
Last updated: 01 December 2021
<br>
Copyright &copy; 1997-2021 University of Cambridge.
<br>

159
doc/pcre2.txt
View File

@ -4899,57 +4899,63 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
This document describes some of the differences in the ways that PCRE2
and Perl handle regular expressions. The differences described here are
with respect to Perl version 5.32.0, but as both Perl and PCRE2 are
with respect to Perl version 5.34.0, but as both Perl and PCRE2 are
continually changing, the information may at times be out of date.
1. PCRE2 has only a subset of Perl's Unicode support. Details of what
1. When PCRE2_DOTALL (equivalent to Perl's /s qualifier) is not set,
the behaviour of the '.' metacharacter differs from Perl. In PCRE2, '.'
matches the next character unless it is the start of a newline se-
quence. This means that, if the newline setting is CR, CRLF, or NUL,
'.' will match the code point LF (0x0A) in ASCII/Unicode environments,
and NL (either 0x15 or 0x25) when using EBCDIC. In Perl, '.' appears
never to match LF, even when 0x0A is not a newline indicator.
2. PCRE2 has only a subset of Perl's Unicode support. Details of what
it does have are given in the pcre2unicode page.
2. Like Perl, PCRE2 allows repeat quantifiers on parenthesized asser-
3. Like Perl, PCRE2 allows repeat quantifiers on parenthesized asser-
tions, but they do not mean what you might think. For example, (?!a){3}
does not assert that the next three characters are not "a". It just as-
serts that the next character is not "a" three times (in principle;
PCRE2 optimizes this to run the assertion just once). Perl allows some
repeat quantifiers on other assertions, for example, \b* (but not
\b{3}, though oddly it does allow ^{3}), but these do not seem to have
any use. PCRE2 does not allow any kind of quantifier on non-lookaround
assertions.
repeat quantifiers on other assertions, for example, \b* , but these do
not seem to have any use. PCRE2 does not allow any kind of quantifier
on non-lookaround assertions.
3. Capture groups that occur inside negative lookaround assertions are
counted, but their entries in the offsets vector are set only when a
negative assertion is a condition that has a matching branch (that is,
the condition is false). Perl may set such capture groups in other
4. Capture groups that occur inside negative lookaround assertions are
counted, but their entries in the offsets vector are set only when a
negative assertion is a condition that has a matching branch (that is,
the condition is false). Perl may set such capture groups in other
circumstances.
4. The following Perl escape sequences are not supported: \F, \l, \L,
5. The following Perl escape sequences are not supported: \F, \l, \L,
\u, \U, and \N when followed by a character name. \N on its own, match-
ing a non-newline character, and \N{U+dd..}, matching a Unicode code
point, are supported. The escapes that modify the case of following
letters are implemented by Perl's general string-handling and are not
ing a non-newline character, and \N{U+dd..}, matching a Unicode code
point, are supported. The escapes that modify the case of following
letters are implemented by Perl's general string-handling and are not
part of its pattern matching engine. If any of these are encountered by
PCRE2, an error is generated by default. However, if either of the
PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are
PCRE2, an error is generated by default. However, if either of the
PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are
interpreted as ECMAScript interprets them.
5. The Perl escape sequences \p, \P, and \X are supported only if PCRE2
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
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".
6. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
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
quotes. In Perl, they cause variable interpolation (but of course PCRE2
does not have variables). Also, Perl does "double-quotish backslash in-
terpolation" on any backslashes between \Q and \E which, its documenta-
tion says, "may lead to confusing results". PCRE2 treats a backslash
between \Q and \E just like any other character. Note the following ex-
amples:
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
just like any other character. Note the following examples:
Pattern PCRE2 matches Perl matches
@ -4963,16 +4969,16 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
The \Q...\E sequence is recognized both inside and outside character
classes by both PCRE2 and Perl.
7. 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.
8. Subroutine calls (whether recursive or not) were treated as atomic
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.
9. In PCRE2, if any of the backtracking control verbs are used in a
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,
@ -4981,18 +4987,18 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
| characters. Note that such groups are processed as anchored at the
point where they are tested.
10. If a pattern contains more than one backtracking control verb, the
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.
11. There are some differences that are concerned with the settings of
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".
12. PCRE2's handling of duplicate capture group numbers and names is
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
@ -5002,90 +5008,91 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
group matched, because both names map to capture group number 1. To
avoid this confusing situation, an error is given at compile time.
13. Perl used to recognize comments in some places that PCRE2 does not,
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
may still be some cases where Perl behaves differently.
14. Perl, when in warning mode, gives warnings for character classes
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.
15. In PCRE2, the upper/lower case character properties Lu and Ll are
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 (5.32), \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.
16. From release 5.32.0, Perl locks out the use of \K in lookaround as-
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,
but is ignored in negative assertions.
17. PCRE2 provides some extensions to the Perl regular expression fa-
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 5.32:
PCRE2 for some time before. This list is with respect to Perl 5.34:
(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 requires them all to have the
same 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.
18. 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.
19. Perl has different limits than PCRE2. See the pcre2limit documenta-
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.
@ -5098,7 +5105,7 @@ AUTHOR
REVISION
Last updated: 30 August 2021
Last updated: 01 December 2021
Copyright (c) 1997-2021 University of Cambridge.
------------------------------------------------------------------------------
@ -7277,14 +7284,16 @@ 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-
fies the end of a line.
fies the end of a line. One or more characters may be specified as line
terminators (see "Newline conventions" above).
When a line ending is defined as a single character, dot never matches
that character; when the two-character sequence CRLF is used, dot does
not match CR if it is immediately followed by LF, but otherwise it
matches all characters (including isolated CRs and LFs). When any Uni-
code line endings are being recognized, dot does not match CR or LF or
any of the other line ending characters.
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
@ -9650,7 +9659,7 @@ AUTHOR
REVISION
Last updated: 30 August 2021
Last updated: 01 December 2021
Copyright (c) 1997-2021 University of Cambridge.
------------------------------------------------------------------------------

74
doc/pcre2compat.3
View File

@ -1,4 +1,4 @@
.TH PCRE2COMPAT 3 "30 August 2021" "PCRE2 10.38"
.TH PCRE2COMPAT 3 "01 December 2021" "PCRE2 10.40"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "DIFFERENCES BETWEEN PCRE2 AND PERL"
@ -6,31 +6,38 @@ PCRE2 - Perl-compatible regular expressions (revised API)
.sp
This document describes some of the differences in the ways that PCRE2 and Perl
handle regular expressions. The differences described here are with respect to
Perl version 5.32.0, but as both Perl and PCRE2 are continually changing, the
Perl version 5.34.0, but as both Perl and PCRE2 are continually changing, the
information may at times be out of date.
.P
1. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
1. When PCRE2_DOTALL (equivalent to Perl's /s qualifier) is not set, the
behaviour of the '.' metacharacter differs from Perl. In PCRE2, '.' matches the
next character unless it is the start of a newline sequence. This means that,
if the newline setting is CR, CRLF, or NUL, '.' will match the code point LF
(0x0A) in ASCII/Unicode environments, and NL (either 0x15 or 0x25) when using
EBCDIC. In Perl, '.' appears never to match LF, even when 0x0A is not a newline
indicator.
.P
2. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
have are given in the
.\" HREF
\fBpcre2unicode\fP
.\"
page.
.P
2. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
3. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
they do not mean what you might think. For example, (?!a){3} does not assert
that the next three characters are not "a". It just asserts that the next
character is not "a" three times (in principle; PCRE2 optimizes this to run the
assertion just once). Perl allows some repeat quantifiers on other assertions,
for example, \eb* (but not \eb{3}, though oddly it does allow ^{3}), but these
do not seem to have any use. PCRE2 does not allow any kind of quantifier on
non-lookaround assertions.
for example, \eb* , but these do not seem to have any use. PCRE2 does not allow
any kind of quantifier on non-lookaround assertions.
.P
3. Capture groups that occur inside negative lookaround assertions are counted,
4. Capture groups that occur inside negative lookaround assertions are counted,
but their entries in the offsets vector are set only when a negative assertion
is a condition that has a matching branch (that is, the condition is false).
Perl may set such capture groups in other circumstances.
.P
4. The following Perl escape sequences are not supported: \eF, \el, \eL, \eu,
5. The following Perl escape sequences are not supported: \eF, \el, \eL, \eu,
\eU, and \eN when followed by a character name. \eN on its own, matching a
non-newline character, and \eN{U+dd..}, matching a Unicode code point, are
supported. The escapes that modify the case of following letters are
@ -40,7 +47,7 @@ generated by default. However, if either of the PCRE2_ALT_BSUX or
PCRE2_EXTRA_ALT_BSUX options is set, \eU and \eu are interpreted as ECMAScript
interprets them.
.P
5. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE2 is
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&.
@ -53,14 +60,14 @@ documentation for details. The long synonyms for property names that Perl
supports (such as \ep{Letter}) are not supported by PCRE2, nor is it permitted
to prefix any of these properties with "Is".
.P
6. PCRE2 supports the \eQ...\eE escape for quoting substrings. Characters
7. PCRE2 supports the \eQ...\eE 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 quotes. In Perl,
they cause variable interpolation (but of course PCRE2 does not have
variables). Also, Perl does "double-quotish backslash interpolation" on any
backslashes between \eQ and \eE which, its documentation says, "may lead to
confusing results". PCRE2 treats a backslash between \eQ and \eE just like any
other character. Note the following examples:
they cause variable interpolation (PCRE2 does not have variables). Also, Perl
does "double-quotish backslash interpolation" on any backslashes between \eQ
and \eE which, its documentation says, "may lead to confusing results". PCRE2
treats a backslash between \eQ and \eE just like any other character. Note the
following examples:
.sp
Pattern PCRE2 matches Perl matches
.sp
@ -75,7 +82,7 @@ other character. Note the following examples:
The \eQ...\eE sequence is recognized both inside and outside character classes
by both PCRE2 and Perl.
.P
7. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code})
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
.\" HREF
@ -83,11 +90,11 @@ external function to be called during pattern matching. See the
.\"
documentation for details.
.P
8. Subroutine calls (whether recursive or not) were treated as atomic groups up
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.
.P
9. In PCRE2, if any of the backtracking control verbs are used in a group that
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 surrounding pattern. This is
not always the case in Perl. In particular, if (*THEN) is present in a group
@ -95,18 +102,18 @@ 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 point where they are tested.
.P
10. If a pattern contains more than one backtracking control verb, the first
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.
.P
11. There are some differences that are concerned with the settings of captured
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 unset, but in PCRE2 it is set to
"b".
.P
12. PCRE2's handling of duplicate capture group numbers and names is not as
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 translate between numbers and
names. In particular, a pattern such as (?|(?<a>A)|(?<b>B)), where the two
@ -115,37 +122,38 @@ 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 avoid this confusing situation, an error is given at compile time.
.P
13. Perl used to recognize comments in some places that PCRE2 does not, for
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 may still be some cases where
Perl behaves differently.
.P
14. Perl, when in warning mode, gives warnings for character classes such as
15. Perl, when in warning mode, gives warnings for character classes such as
[A-\ed] or [a-[:digit:]]. It then treats the hyphens as literals. PCRE2 has no
warning features, so it gives an error in these cases because they are almost
certainly user mistakes.
.P
15. In PCRE2, the upper/lower case character properties Lu and Ll are not
16. In PCRE2, the upper/lower case character properties Lu and Ll are not
affected when case-independent matching is specified. For example, \ep{Lu}
always matches an upper case letter. I think Perl has changed in this respect;
in the release at the time of writing (5.32), \ep{Lu} and \ep{Ll} match all
in the release at the time of writing (5.34), \ep{Lu} and \ep{Ll} match all
letters, regardless of case, when case independence is specified.
.P
16. From release 5.32.0, Perl locks out the use of \eK in lookaround
17. From release 5.32.0, Perl locks out the use of \eK in lookaround
assertions. 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,
\eK is acted on when it occurs in positive assertions, but is ignored in
negative assertions.
.P
17. PCRE2 provides some extensions to the Perl regular expression facilities.
18. PCRE2 provides some extensions to the Perl regular expression facilities.
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 5.32:
list is with respect to Perl 5.34:
.sp
(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 requires them all to have the same length.
different length of string. Perl used to require them all to have the same
length, but the latest version has some variable length support.
.sp
(b) From PCRE2 10.23, backreferences to groups of fixed length are supported
in lookbehinds, provided that there is no possibility of referencing a
@ -186,11 +194,11 @@ the pattern.
extension to the lookaround facilities. The default, Perl-compatible
lookarounds are atomic.
.P
18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
19. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
modifier restricts /i case-insensitive matching to pure ascii, ignoring Unicode
rules. This separation cannot be represented with PCRE2_UCP.
.P
19. Perl has different limits than PCRE2. See the
20. Perl has different limits than PCRE2. See the
.\" HREF
\fBpcre2limit\fP
.\"
@ -214,6 +222,6 @@ Cambridge, England.
.rs
.sp
.nf
Last updated: 30 August 2021
Last updated: 01 December 2021
Copyright (c) 1997-2021 University of Cambridge.
.fi

23
doc/pcre2pattern.3
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@ -1,4 +1,4 @@
.TH PCRE2PATTERN 3 "3o0 August 2021" "PCRE2 10.38"
.TH PCRE2PATTERN 3 "01 December 2021" "PCRE2 10.40"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "PCRE2 REGULAR EXPRESSION DETAILS"
@ -1335,14 +1335,19 @@ end of the subject in both modes, and if all branches of a pattern start with
.sp
Outside a character class, a dot in the pattern matches any one character in
the subject string except (by default) a character that signifies the end of a
line.
line. One or more characters may be specified as line terminators (see
.\" HTML <a href="#newlines">
.\" </a>
"Newline conventions"
.\"
above).
.P
When a line ending is defined as a single character, dot never matches that
character; when the two-character sequence CRLF is used, dot does not match CR
if it is immediately followed by LF, but otherwise it matches all characters
(including isolated CRs and LFs). When any Unicode line endings are being
recognized, dot does not match CR or LF or any of the other line ending
characters.
Dot never matches a single line-ending character. When the two-character
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.
.P
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.
@ -3904,6 +3909,6 @@ Cambridge, England.
.rs
.sp
.nf
Last updated: 30 August 2021
Last updated: 01 December 2021
Copyright (c) 1997-2021 University of Cambridge.
.fi