--- embedaddon/pcre/doc/pcrecompat.3 2012/02/21 23:05:52 1.1.1.1 +++ embedaddon/pcre/doc/pcrecompat.3 2014/06/15 19:46:05 1.1.1.5 @@ -1,4 +1,4 @@ -.TH PCRECOMPAT 3 +.TH PCRECOMPAT 3 "10 November 2013" "PCRE 8.34" .SH NAME PCRE - Perl-compatible regular expressions .SH "DIFFERENCES BETWEEN PCRE AND PERL" @@ -8,8 +8,8 @@ This document describes the differences in the ways th regular expressions. The differences described here are with respect to Perl versions 5.10 and above. .P -1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what -it does have are given in the +1. PCRE has only a subset of Perl's Unicode support. Details of what it does +have are given in the .\" HREF \fBpcreunicode\fP .\" @@ -23,10 +23,8 @@ just once). Perl allows repeat quantifiers on other as these do not seem to have any use. .P 3. Capturing subpatterns that occur inside negative lookahead assertions are -counted, but their entries in the offsets vector are never set. Perl sets its -numerical variables from any such patterns that are matched before the -assertion fails to match something (thereby succeeding), but only if the -negative lookahead assertion contains just one branch. +counted, but their entries in the offsets vector are never set. Perl sometimes +(but not always) sets its numerical variables from inside negative assertions. .P 4. Though binary zero characters are supported in the subject string, they are not allowed in a pattern string because it is passed as a normal C string, @@ -50,11 +48,7 @@ Perl documentation says "Because Perl hides the need f the internal representation of Unicode characters, there is no need to implement the somewhat messy concept of surrogates." .P -7. PCRE implements a simpler version of \eX than Perl, which changed to make -\eX match what Unicode calls an "extended grapheme cluster". This is more -complicated than an extended Unicode sequence, which is what PCRE matches. -.P -8. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in +7. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in between are treated as literals. 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 PCRE does not have variables). Note the @@ -70,7 +64,7 @@ following examples: .sp The \eQ...\eE sequence is recognized both inside and outside character classes. .P -9. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) +8. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) constructions. However, there is support for recursive patterns. This is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout" feature allows an external function to be called during pattern matching. See @@ -80,7 +74,7 @@ the .\" documentation for details. .P -10. Subpatterns that are called as subroutines (whether or not recursively) are +9. Subpatterns that are called as subroutines (whether or not recursively) are always treated as atomic groups in PCRE. This is like Python, but unlike Perl. Captured values that are set outside a subroutine call can be reference from inside in PCRE, but not in Perl. There is a discussion that explains these @@ -95,14 +89,28 @@ in the .\" page. .P -11. If (*THEN) is present in a group that is called as a subroutine, its action -is limited to that group, even if the group does not contain any | characters. +10. If any of the backtracking control verbs are used in a subpattern that is +called as a subroutine (whether or not recursively), their effect is confined +to that subpattern; 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 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 subpatterns are +processed as anchored at the point where they are tested. .P -12. There are some differences that are concerned with the settings of captured +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 PCRE, but there are examples where it differs. +.P +12. Most backtracking verbs in assertions have their normal actions. They are +not confined to the assertion. +.P +13. 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 PCRE it is set to "b". .P -13. PCRE's handling of duplicate subpattern numbers and duplicate subpattern +14. PCRE's handling of duplicate subpattern numbers and duplicate subpattern names is not as general as Perl's. This is a consequence of the fact the PCRE works internally just with numbers, using an external table to translate between numbers and names. In particular, a pattern such as (?|(?A)|(?