Documentation update
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Philip Hazel
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@ -18,33 +18,41 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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<P>
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This document describes some of the differences in the ways that PCRE2 and Perl
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handle regular expressions. The differences described here are with respect to
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Perl version 5.32.0, but as both Perl and PCRE2 are continually changing, the
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Perl version 5.34.0, but as both Perl and PCRE2 are continually changing, the
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information may at times be out of date.
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</P>
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<P>
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1. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
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1. When PCRE2_DOTALL (equivalent to Perl's /s qualifier) is not set, the
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behaviour of the '.' metacharacter differs from Perl. In PCRE2, '.' matches the
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next character unless it is the start of a newline sequence. This means that,
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if the newline setting is CR, CRLF, or NUL, '.' will match the code point LF
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(0x0A) in ASCII/Unicode environments, and NL (either 0x15 or 0x25) when using
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EBCDIC. In Perl, '.' appears never to match LF, even when 0x0A is not a newline
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indicator.
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</P>
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<P>
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2. PCRE2 has only a subset of Perl's Unicode support. Details of what it does
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have are given in the
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<a href="pcre2unicode.html"><b>pcre2unicode</b></a>
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page.
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</P>
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<P>
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2. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
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3. Like Perl, PCRE2 allows repeat quantifiers on parenthesized assertions, but
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they do not mean what you might think. For example, (?!a){3} does not assert
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that the next three characters are not "a". It just asserts that the next
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character is not "a" three times (in principle; PCRE2 optimizes this to run the
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assertion just once). Perl allows some repeat quantifiers on other assertions,
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for example, \b* (but not \b{3}, though oddly it does allow ^{3}), but these
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do not seem to have any use. PCRE2 does not allow any kind of quantifier on
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non-lookaround assertions.
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for example, \b* , but these do not seem to have any use. PCRE2 does not allow
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any kind of quantifier on non-lookaround assertions.
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</P>
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<P>
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3. Capture groups that occur inside negative lookaround assertions are counted,
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4. Capture groups that occur inside negative lookaround assertions are counted,
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but their entries in the offsets vector are set only when a negative assertion
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is a condition that has a matching branch (that is, the condition is false).
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Perl may set such capture groups in other circumstances.
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</P>
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<P>
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4. The following Perl escape sequences are not supported: \F, \l, \L, \u,
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5. The following Perl escape sequences are not supported: \F, \l, \L, \u,
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\U, and \N when followed by a character name. \N on its own, matching a
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non-newline character, and \N{U+dd..}, matching a Unicode code point, are
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supported. The escapes that modify the case of following letters are
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@ -55,7 +63,7 @@ PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are interpreted as ECMAScript
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interprets them.
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</P>
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<P>
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5. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is
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6. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is
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built with Unicode support (the default). The properties that can be tested
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with \p and \P are limited to the general category properties such as Lu and
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Nd, script names such as Greek or Han, and the derived properties Any and L&.
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@ -67,14 +75,14 @@ supports (such as \p{Letter}) are not supported by PCRE2, nor is it permitted
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to prefix any of these properties with "Is".
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</P>
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<P>
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6. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
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7. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
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in between are treated as literals. However, this is slightly different from
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Perl in that $ and @ are also handled as literals inside the quotes. In Perl,
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they cause variable interpolation (but of course PCRE2 does not have
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variables). Also, Perl does "double-quotish backslash interpolation" on any
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backslashes between \Q and \E which, its documentation says, "may lead to
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confusing results". PCRE2 treats a backslash between \Q and \E just like any
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other character. Note the following examples:
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they cause variable interpolation (PCRE2 does not have variables). Also, Perl
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does "double-quotish backslash interpolation" on any backslashes between \Q
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and \E which, its documentation says, "may lead to confusing results". PCRE2
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treats a backslash between \Q and \E just like any other character. Note the
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following examples:
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<pre>
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Pattern PCRE2 matches Perl matches
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@ -88,19 +96,19 @@ The \Q...\E sequence is recognized both inside and outside character classes
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by both PCRE2 and Perl.
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</P>
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<P>
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7. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code})
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8. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code})
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constructions. However, PCRE2 does have a "callout" feature, which allows an
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external function to be called during pattern matching. See the
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<a href="pcre2callout.html"><b>pcre2callout</b></a>
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documentation for details.
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</P>
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<P>
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8. Subroutine calls (whether recursive or not) were treated as atomic groups up
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9. Subroutine calls (whether recursive or not) were treated as atomic groups up
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to PCRE2 release 10.23, but from release 10.30 this changed, and backtracking
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into subroutine calls is now supported, as in Perl.
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</P>
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<P>
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9. In PCRE2, if any of the backtracking control verbs are used in a group that
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10. In PCRE2, if any of the backtracking control verbs are used in a group that
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is called as a subroutine (whether or not recursively), their effect is
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confined to that group; it does not extend to the surrounding pattern. This is
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not always the case in Perl. In particular, if (*THEN) is present in a group
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@ -109,20 +117,20 @@ the group does not contain any | characters. Note that such groups are
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processed as anchored at the point where they are tested.
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</P>
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<P>
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10. If a pattern contains more than one backtracking control verb, the first
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11. If a pattern contains more than one backtracking control verb, the first
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one that is backtracked onto acts. For example, in the pattern
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A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure in C
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triggers (*PRUNE). Perl's behaviour is more complex; in many cases it is the
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same as PCRE2, but there are cases where it differs.
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</P>
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<P>
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11. There are some differences that are concerned with the settings of captured
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12. There are some differences that are concerned with the settings of captured
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strings when part of a pattern is repeated. For example, matching "aba" against
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the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE2 it is set to
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"b".
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</P>
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<P>
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12. PCRE2's handling of duplicate capture group numbers and names is not as
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13. PCRE2's handling of duplicate capture group numbers and names is not as
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general as Perl's. This is a consequence of the fact the PCRE2 works internally
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just with numbers, using an external table to translate between numbers and
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names. In particular, a pattern such as (?|(?<a>A)|(?<b>B)), where the two
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@ -132,42 +140,43 @@ to distinguish which group matched, because both names map to capture group
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number 1. To avoid this confusing situation, an error is given at compile time.
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</P>
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<P>
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13. Perl used to recognize comments in some places that PCRE2 does not, for
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14. Perl used to recognize comments in some places that PCRE2 does not, for
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example, between the ( and ? at the start of a group. If the /x modifier is
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set, Perl allowed white space between ( and ? though the latest Perls give an
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error (for a while it was just deprecated). There may still be some cases where
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Perl behaves differently.
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</P>
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<P>
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14. Perl, when in warning mode, gives warnings for character classes such as
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15. Perl, when in warning mode, gives warnings for character classes such as
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[A-\d] or [a-[:digit:]]. It then treats the hyphens as literals. PCRE2 has no
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warning features, so it gives an error in these cases because they are almost
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certainly user mistakes.
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</P>
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<P>
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15. In PCRE2, the upper/lower case character properties Lu and Ll are not
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16. In PCRE2, the upper/lower case character properties Lu and Ll are not
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affected when case-independent matching is specified. For example, \p{Lu}
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always matches an upper case letter. I think Perl has changed in this respect;
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in the release at the time of writing (5.32), \p{Lu} and \p{Ll} match all
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in the release at the time of writing (5.34), \p{Lu} and \p{Ll} match all
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letters, regardless of case, when case independence is specified.
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</P>
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<P>
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16. From release 5.32.0, Perl locks out the use of \K in lookaround
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17. From release 5.32.0, Perl locks out the use of \K in lookaround
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assertions. From release 10.38 PCRE2 does the same by default. However, there
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is an option for re-enabling the previous behaviour. When this option is set,
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\K is acted on when it occurs in positive assertions, but is ignored in
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negative assertions.
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</P>
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<P>
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17. PCRE2 provides some extensions to the Perl regular expression facilities.
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18. PCRE2 provides some extensions to the Perl regular expression facilities.
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Perl 5.10 included new features that were not in earlier versions of Perl, some
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of which (such as named parentheses) were in PCRE2 for some time before. This
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list is with respect to Perl 5.32:
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list is with respect to Perl 5.34:
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<br>
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<br>
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(a) Although lookbehind assertions in PCRE2 must match fixed length strings,
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each alternative toplevel branch of a lookbehind assertion can match a
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different length of string. Perl requires them all to have the same length.
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different length of string. Perl used to require them all to have the same
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length, but the latest version has some variable length support.
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<br>
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<br>
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(b) From PCRE2 10.23, backreferences to groups of fixed length are supported
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@ -221,12 +230,12 @@ extension to the lookaround facilities. The default, Perl-compatible
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lookarounds are atomic.
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</P>
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<P>
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18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
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19. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
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modifier restricts /i case-insensitive matching to pure ascii, ignoring Unicode
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rules. This separation cannot be represented with PCRE2_UCP.
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</P>
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<P>
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19. Perl has different limits than PCRE2. See the
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20. Perl has different limits than PCRE2. See the
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<a href="pcre2limit.html"><b>pcre2limit</b></a>
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documentation for details. Perl went with 5.10 from recursion to iteration
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keeping the intermediate matches on the heap, which is ~10% slower but does not
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@ -248,7 +257,7 @@ Cambridge, England.
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REVISION
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</b><br>
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<P>
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Last updated: 30 August 2021
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Last updated: 01 December 2021
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<br>
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Copyright © 1997-2021 University of Cambridge.
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<br>
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@ -1341,15 +1341,17 @@ end of the subject in both modes, and if all branches of a pattern start with
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<P>
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Outside a character class, a dot in the pattern matches any one character in
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the subject string except (by default) a character that signifies the end of a
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line.
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line. One or more characters may be specified as line terminators (see
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<a href="#newlines">"Newline conventions"</a>
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above).
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</P>
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<P>
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When a line ending is defined as a single character, dot never matches that
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character; when the two-character sequence CRLF is used, dot does not match CR
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if it is immediately followed by LF, but otherwise it matches all characters
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(including isolated CRs and LFs). When any Unicode line endings are being
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recognized, dot does not match CR or LF or any of the other line ending
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characters.
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Dot never matches a single line-ending character. When the two-character
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sequence CRLF is the only line ending, dot does not match CR if it is
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immediately followed by LF, but otherwise it matches all characters (including
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isolated CRs and LFs). When ANYCRLF is selected for line endings, no occurences
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of CR of LF match dot. When all Unicode line endings are being recognized, dot
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does not match CR or LF or any of the other line ending characters.
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</P>
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<P>
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The behaviour of dot with regard to newlines can be changed. If the
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@ -3859,7 +3861,7 @@ Cambridge, England.
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</P>
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<br><a name="SEC32" href="#TOC1">REVISION</a><br>
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<P>
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Last updated: 30 August 2021
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Last updated: 01 December 2021
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<br>
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Copyright © 1997-2021 University of Cambridge.
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<br>
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|
|
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@ -4899,29 +4899,36 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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This document describes some of the differences in the ways that PCRE2
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and Perl handle regular expressions. The differences described here are
|
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with respect to Perl version 5.32.0, but as both Perl and PCRE2 are
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with respect to Perl version 5.34.0, but as both Perl and PCRE2 are
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continually changing, the information may at times be out of date.
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1. PCRE2 has only a subset of Perl's Unicode support. Details of what
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1. When PCRE2_DOTALL (equivalent to Perl's /s qualifier) is not set,
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the behaviour of the '.' metacharacter differs from Perl. In PCRE2, '.'
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matches the next character unless it is the start of a newline se-
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quence. This means that, if the newline setting is CR, CRLF, or NUL,
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'.' will match the code point LF (0x0A) in ASCII/Unicode environments,
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and NL (either 0x15 or 0x25) when using EBCDIC. In Perl, '.' appears
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never to match LF, even when 0x0A is not a newline indicator.
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2. PCRE2 has only a subset of Perl's Unicode support. Details of what
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it does have are given in the pcre2unicode page.
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2. Like Perl, PCRE2 allows repeat quantifiers on parenthesized asser-
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3. Like Perl, PCRE2 allows repeat quantifiers on parenthesized asser-
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tions, but they do not mean what you might think. For example, (?!a){3}
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does not assert that the next three characters are not "a". It just as-
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serts that the next character is not "a" three times (in principle;
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PCRE2 optimizes this to run the assertion just once). Perl allows some
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repeat quantifiers on other assertions, for example, \b* (but not
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\b{3}, though oddly it does allow ^{3}), but these do not seem to have
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any use. PCRE2 does not allow any kind of quantifier on non-lookaround
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assertions.
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repeat quantifiers on other assertions, for example, \b* , but these do
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not seem to have any use. PCRE2 does not allow any kind of quantifier
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on non-lookaround assertions.
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3. Capture groups that occur inside negative lookaround assertions are
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4. Capture groups that occur inside negative lookaround assertions are
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counted, but their entries in the offsets vector are set only when a
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negative assertion is a condition that has a matching branch (that is,
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the condition is false). Perl may set such capture groups in other
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circumstances.
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4. The following Perl escape sequences are not supported: \F, \l, \L,
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5. The following Perl escape sequences are not supported: \F, \l, \L,
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\u, \U, and \N when followed by a character name. \N on its own, match-
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ing a non-newline character, and \N{U+dd..}, matching a Unicode code
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point, are supported. The escapes that modify the case of following
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@ -4931,7 +4938,7 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are
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interpreted as ECMAScript interprets them.
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5. The Perl escape sequences \p, \P, and \X are supported only if PCRE2
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6. The Perl escape sequences \p, \P, and \X are supported only if PCRE2
|
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is built with Unicode support (the default). The properties that can be
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tested with \p and \P are limited to the general category properties
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such as Lu and Nd, script names such as Greek or Han, and the derived
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|
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@ -4941,15 +4948,14 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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supports (such as \p{Letter}) are not supported by PCRE2, nor is it
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permitted to prefix any of these properties with "Is".
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6. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
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7. PCRE2 supports the \Q...\E escape for quoting substrings. Characters
|
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in between are treated as literals. However, this is slightly different
|
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from Perl in that $ and @ are also handled as literals inside the
|
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quotes. In Perl, they cause variable interpolation (but of course PCRE2
|
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does not have variables). Also, Perl does "double-quotish backslash in-
|
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terpolation" on any backslashes between \Q and \E which, its documenta-
|
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tion says, "may lead to confusing results". PCRE2 treats a backslash
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between \Q and \E just like any other character. Note the following ex-
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amples:
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quotes. In Perl, they cause variable interpolation (PCRE2 does not have
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variables). Also, Perl does "double-quotish backslash interpolation" on
|
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any backslashes between \Q and \E which, its documentation says, "may
|
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lead to confusing results". PCRE2 treats a backslash between \Q and \E
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just like any other character. Note the following examples:
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Pattern PCRE2 matches Perl matches
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@ -4963,16 +4969,16 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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The \Q...\E sequence is recognized both inside and outside character
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classes by both PCRE2 and Perl.
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7. Fairly obviously, PCRE2 does not support the (?{code}) and
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8. Fairly obviously, PCRE2 does not support the (?{code}) and
|
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(??{code}) constructions. However, PCRE2 does have a "callout" feature,
|
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which allows an external function to be called during pattern matching.
|
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See the pcre2callout documentation for details.
|
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8. Subroutine calls (whether recursive or not) were treated as atomic
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9. Subroutine calls (whether recursive or not) were treated as atomic
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groups up to PCRE2 release 10.23, but from release 10.30 this changed,
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and backtracking into subroutine calls is now supported, as in Perl.
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|
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9. In PCRE2, if any of the backtracking control verbs are used in a
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10. In PCRE2, if any of the backtracking control verbs are used in a
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group that is called as a subroutine (whether or not recursively),
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their effect is confined to that group; it does not extend to the sur-
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rounding pattern. This is not always the case in Perl. In particular,
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|
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@ -4981,18 +4987,18 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
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| characters. Note that such groups are processed as anchored at the
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point where they are tested.
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10. If a pattern contains more than one backtracking control verb, the
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11. If a pattern contains more than one backtracking control verb, the
|
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first one that is backtracked onto acts. For example, in the pattern
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A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure
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in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases
|
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it is the same as PCRE2, but there are cases where it differs.
|
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|
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11. There are some differences that are concerned with the settings of
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12. There are some differences that are concerned with the settings of
|
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captured strings when part of a pattern is repeated. For example,
|
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matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 un-
|
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set, but in PCRE2 it is set to "b".
|
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|
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12. PCRE2's handling of duplicate capture group numbers and names is
|
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13. PCRE2's handling of duplicate capture group numbers and names is
|
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not as general as Perl's. This is a consequence of the fact the PCRE2
|
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works internally just with numbers, using an external table to trans-
|
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late between numbers and names. In particular, a pattern such as
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|
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@ -5002,39 +5008,40 @@ 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-
|
||||
|
|
@ -5076,12 +5083,12 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
|
|||
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
|
||||
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
|
||||
|
|
@ -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.
|
||||
------------------------------------------------------------------------------
|
||||
|
||||
|
|
|
|||
|
|
@ -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
|
||||
|
|
|
|||
|
|
@ -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
|
||||
|
|
|
|||
Loading…
Reference in New Issue