X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlre.pod;h=42017ddf6629661a082bb46ab08273ae43864308;hb=93592fd5aeec89ac25994a493ef54e1d7a572d65;hp=c35b49fe72e0c9ac42645f815eba33d331515a25;hpb=e1f17637d1ade6d468d3aebe31c7b7a17f6fc053;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlre.pod b/pod/perlre.pod index c35b49f..42017dd 100644 --- a/pod/perlre.pod +++ b/pod/perlre.pod @@ -62,7 +62,7 @@ Extend your pattern's legibility by permitting whitespace and comments. =item p X

X X -Preserve the string matched such that ${^PREMATCH}, {$^MATCH}, and +Preserve the string matched such that ${^PREMATCH}, ${^MATCH}, and ${^POSTMATCH} are available for use after matching. =item g and c @@ -102,7 +102,7 @@ X =head3 Metacharacters -The patterns used in Perl pattern matching evolved from the ones supplied in +The patterns used in Perl pattern matching evolved from those supplied in the Version 8 regex routines. (The routines are derived (distantly) from Henry Spencer's freely redistributable reimplementation of the V8 routines.) See L for @@ -271,6 +271,7 @@ X X X X \g{name} Named backreference \k Named backreference \K Keep the stuff left of the \K, don't include it in $& + \N Any character but \n \v Vertical whitespace \V Not vertical whitespace \h Horizontal whitespace @@ -315,26 +316,34 @@ they must always be used within a character class expression. # this is not, and will generate a warning: $string =~ /[:alpha:]/; -The available classes and their backslash equivalents (if available) are -as follows: -X +The following table shows the mapping of POSIX character class +names, common escapes, literal escape sequences and their equivalent +Unicode style property names. +X X<\p> X<\p{}> X X X X X X X X X X X X X X - alpha - alnum - ascii - blank [1] - cntrl - digit \d - graph - lower - print - punct - space \s [2] - upper - word \w [3] - xdigit +B up to Perl 5.10 the property names used were shared with +standard Unicode properties, this was changed in Perl 5.11, see +L for details. + + POSIX Esc Class Property Note + -------------------------------------------------------- + alnum [0-9A-Za-z] IsPosixAlnum + alpha [A-Za-z] IsPosixAlpha + ascii [\000-\177] IsASCII + blank [\011 ] IsPosixBlank [1] + cntrl [\0-\37\177] IsPosixCntrl + digit \d [0-9] IsPosixDigit + graph [!-~] IsPosixGraph + lower [a-z] IsPosixLower + print [ -~] IsPosixPrint + punct [!-/:-@[-`{-~] IsPosixPunct + space [\11-\15 ] IsPosixSpace [2] + \s [\11\12\14\15 ] IsPerlSpace [2] + upper [A-Z] IsPosixUpper + word \w [0-9A-Z_a-z] IsPerlWord [3] + xdigit [0-9A-Fa-f] IsXDigit =over @@ -344,8 +353,9 @@ A GNU extension equivalent to C<[ \t]>, "all horizontal whitespace". =item [2] -Not exactly equivalent to C<\s> since the C<[[:space:]]> includes -also the (very rare) "vertical tabulator", "\cK" or chr(11) in ASCII. +Note that C<\s> and C<[[:space:]]> are B equivalent as C<[[:space:]]> +includes also the (very rare) "vertical tabulator", "\cK" or chr(11) in +ASCII. =item [3] @@ -361,33 +371,22 @@ whole character class. For example: matches zero, one, any alphabetic character, and the percent sign. -The following equivalences to Unicode \p{} constructs and equivalent -backslash character classes (if available), will hold: -X X<\p> X<\p{}> +=over 4 + +=item C<$> + +Currency symbol + +=item C<+> C<< < >> C<=> C<< > >> C<|> C<~> + +Mathematical symbols + +=item C<^> C<`> - [[:...:]] \p{...} backslash - - alpha IsAlpha - alnum IsAlnum - ascii IsASCII - blank - cntrl IsCntrl - digit IsDigit \d - graph IsGraph - lower IsLower - print IsPrint - punct IsPunct - space IsSpace - IsSpacePerl \s - upper IsUpper - word IsWord - xdigit IsXDigit - -For example C<[[:lower:]]> and C<\p{IsLower}> are equivalent. - -If the C pragma is not used but the C pragma is, the -classes correlate with the usual isalpha(3) interface (except for -"word" and "blank"). +Modifier symbols (accents) + + +=back The other named classes are: @@ -432,9 +431,9 @@ X POSIX traditional Unicode - [[:^digit:]] \D \P{IsDigit} - [[:^space:]] \S \P{IsSpace} - [[:^word:]] \W \P{IsWord} + [[:^digit:]] \D \P{IsPosixDigit} + [[:^space:]] \S \P{IsPosixSpace} + [[:^word:]] \W \P{IsPerlWord} Perl respects the POSIX standard in that POSIX character classes are only supported within a character class. The POSIX character classes @@ -519,6 +518,10 @@ backreference only if at least 11 left parentheses have opened before it. And so on. \1 through \9 are always interpreted as backreferences. +If the bracketing group did not match, the associated backreference won't +match either. (This can happen if the bracketing group is optional, or +in a different branch of an alternation.) + X<\g{1}> X<\g{-1}> X<\g{name}> X X In order to provide a safer and easier way to construct patterns using backreferences, Perl provides the C<\g{N}> notation (starting with perl @@ -704,6 +707,10 @@ will match C in any case, some spaces, and an exact (I repetition of the previous word, assuming the C modifier, and no C modifier outside this group. +These modifiers do not carry over into named subpatterns called in the +enclosing group. In other words, a pattern such as C<((?i)(&NAME))> does not +change the case-sensitivity of the "NAME" pattern. + Note that the C

modifier is special in that it can only be enabled, not disabled, and that its presence anywhere in a pattern has a global effect. Thus C<(?-p)> and C<(?-p:...)> are meaningless and will warn @@ -943,13 +950,6 @@ The assignment to C<$^R> above is properly localized, so the old value of C<$^R> is restored if the assertion is backtracked; compare L<"Backtracking">. -Due to an unfortunate implementation issue, the Perl code contained in these -blocks is treated as a compile time closure that can have seemingly bizarre -consequences when used with lexically scoped variables inside of subroutines -or loops. There are various workarounds for this, including simply using -global variables instead. If you are using this construct and strange results -occur then check for the use of lexically scoped variables. - For reasons of security, this construct is forbidden if the regular expression involves run-time interpolation of variables, unless the perilous C pragma has been used (see L), or the @@ -971,9 +971,15 @@ so you should only do so if you are also using taint checking. Better yet, use the carefully constrained evaluation within a Safe compartment. See L for details about both these mechanisms. -Because Perl's regex engine is currently not re-entrant, interpolated -code may not invoke the regex engine either directly with C or C), -or indirectly with functions such as C. +B: Use of lexical (C) variables in these blocks is +broken. The result is unpredictable and will make perl unstable. The +workaround is to use global (C) variables. + +B: Because Perl's regex engine is currently not re-entrant, +interpolated code may not invoke the regex engine either directly with +C or C), or indirectly with functions such as +C. Invoking the regex engine in these blocks will make perl +unstable. =item C<(??{ code })> X<(??{})>