X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlre.pod;h=15e58c1cf9dd44e0c93ec640a8e0d5a63db85ffc;hb=1f950eb4f39b89f547d5802df0c94526d900d2f2;hp=1610254da57bbbd32c80b1fe2219ba3105f1d9ec;hpb=1209ba901e0b2880eea69ad70613848af5543517;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlre.pod b/pod/perlre.pod index 1610254..15e58c1 100644 --- a/pod/perlre.pod +++ b/pod/perlre.pod @@ -121,7 +121,7 @@ to integral values less than a preset limit defined when perl is built. This is usually 32766 on the most common platforms. The actual limit can be seen in the error message generated by code such as this: - $_ **= $_ , / {$_} / for 2 .. 42; + $_ **= $_ , / {$_} / for 2 .. 42; By default, a quantified subpattern is "greedy", that is, it will match as many times as possible (given a particular starting location) while still @@ -169,7 +169,7 @@ You'll need to write something like C. In addition, Perl defines the following: \w Match a "word" character (alphanumeric plus "_") - \W Match a non-word character + \W Match a non-"word" character \s Match a whitespace character \S Match a non-whitespace character \d Match a digit character @@ -180,7 +180,7 @@ In addition, Perl defines the following: equivalent to C<(?:\PM\pM*)> \C Match a single C char (octet) even under utf8. -A C<\w> matches a single alphanumeric character, not a whole word. +A C<\w> matches a single alphanumeric character or C<_>, not a whole word. Use C<\w+> to match a string of Perl-identifier characters (which isn't the same as matching an English word). If C is in effect, the list of alphabetic characters generated by C<\w> is taken from the @@ -191,7 +191,7 @@ See L for details about C<\pP>, C<\PP>, and C<\X>. The POSIX character class syntax - [:class:] + [:class:] is also available. The available classes and their backslash equivalents (if available) are as follows: @@ -214,7 +214,7 @@ For example use C<[:upper:]> to match all the uppercase characters. Note that the C<[]> are part of the C<[::]> construct, not part of the whole character class. For example: - [01[:alpha:]%] + [01[:alpha:]%] matches one, zero, any alphabetic character, and the percentage sign. @@ -247,31 +247,27 @@ The assumedly non-obviously named classes are: =item cntrl - Any control character. Usually characters that don't produce - output as such but instead control the terminal somehow: - for example newline and backspace are control characters. - All characters with ord() less than 32 are most often control - classified as characters. +Any control character. Usually characters that don't produce output as +such but instead control the terminal somehow: for example newline and +backspace are control characters. All characters with ord() less than +32 are most often classified as control characters. =item graph - Any alphanumeric or punctuation character. +Any alphanumeric or punctuation (special) character. =item print - Any alphanumeric or punctuation character or space. +Any alphanumeric or punctuation (special) character or space. =item punct - Any punctuation character. +Any punctuation (special) character. =item xdigit - Any hexadecimal digit. Though this may feel silly - (/0-9a-f/i would work just fine) it is included - for completeness. - -=item +Any hexadecimal digit. Though this may feel silly (/0-9a-f/i would +work just fine) it is included for completeness. =back @@ -316,11 +312,11 @@ several patterns that you want to match against consequent substrings of your string, see the previous reference. The actual location where C<\G> will match can also be influenced by using C as an lvalue. See L. - + The bracketing construct C<( ... )> creates capture buffers. To -refer to the digit'th buffer use \EdigitE within the +refer to the digit'th buffer use \ within the match. Outside the match use "$" instead of "\". (The -\EdigitE notation works in certain circumstances outside +\ notation works in certain circumstances outside the match. See the warning below about \1 vs $1 for details.) Referring back to another part of the match is called a I. @@ -341,13 +337,13 @@ Examples: if (/(.)\1/) { # find first doubled char print "'$1' is the first doubled character\n"; } - + if (/Time: (..):(..):(..)/) { # parse out values $hours = $1; $minutes = $2; $seconds = $3; } - + Several special variables also refer back to portions of the previous match. C<$+> returns whatever the last bracket match matched. C<$&> returns the entire matched string. (At one point C<$0> did @@ -377,14 +373,15 @@ other two. Backslashed metacharacters in Perl are alphanumeric, such as C<\b>, C<\w>, C<\n>. Unlike some other regular expression languages, there are no backslashed symbols that aren't alphanumeric. So anything -that looks like \\, \(, \), \E, \E, \{, or \} is always +that looks like \\, \(, \), \<, \>, \{, or \} is always interpreted as a literal character, not a metacharacter. This was once used in a common idiom to disable or quote the special meanings of regular expression metacharacters in a string that you want to -use for a pattern. Simply quote all non-alphanumeric characters: +use for a pattern. Simply quote all non-"word" characters: $pattern =~ s/(\W)/\\$1/g; +(If C is set, then this depends on the current locale.) Today it is more common to use the quotemeta() function or the C<\Q> metaquoting escape sequence to disable all metacharacters' special meanings like this: @@ -500,9 +497,9 @@ Sometimes it's still easier just to say: For look-behind see below. -=item C<(?E=pattern)> +=item C<(?<=pattern)> -A zero-width positive look-behind assertion. For example, C=\t)\w+/> +A zero-width positive look-behind assertion. For example, C matches a word that follows a tab, without including the tab in C<$&>. Works only for fixed-width look-behind. @@ -574,7 +571,7 @@ so you should only do so if you are also using taint checking. Better yet, use the carefully constrained evaluation within a Safe module. See L for details about both these mechanisms. -=item C<(?p{ code })> +=item C<(??{ code })> B: This extended regular expression feature is considered highly experimental, and may be changed or deleted without notice. @@ -596,12 +593,12 @@ The following pattern matches a parenthesized group: (?: (?> [^()]+ ) # Non-parens without backtracking | - (?p{ $re }) # Group with matching parens + (??{ $re }) # Group with matching parens )* \) }x; -=item C<(?Epattern)> +=item C<< (?>pattern) >> B: This extended regular expression feature is considered highly experimental, and may be changed or deleted without notice. @@ -614,7 +611,7 @@ construct is useful for optimizations of what would otherwise be It may also be useful in places where the "grab all you can, and do not give anything back" semantic is desirable. -For example: C<^(?Ea*)ab> will never match, since C<(?Ea*)> +For example: C<< ^(?>a*)ab >> will never match, since C<< (?>a*) >> (anchored at the beginning of string, as above) will match I characters C at the beginning of string, leaving no C for C to match. In contrast, C will match the same as C, @@ -623,10 +620,10 @@ group C (see L<"Backtracking">). In particular, C inside C will match fewer characters than a standalone C, since this makes the tail match. -An effect similar to C<(?Epattern)> may be achieved by writing +An effect similar to C<< (?>pattern) >> may be achieved by writing C<(?=(pattern))\1>. This matches the same substring as a standalone C, and the following C<\1> eats the matched string; it therefore -makes a zero-length assertion into an analogue of C<(?E...)>. +makes a zero-length assertion into an analogue of C<< (?>...) >>. (The difference between these two constructs is that the second one uses a capturing group, thus shifting ordinals of backreferences in the rest of a regular expression.) @@ -662,13 +659,14 @@ hung. However, a tiny change to this pattern \) }x -which uses C<(?E...)> matches exactly when the one above does (verifying +which uses C<< (?>...) >> matches exactly when the one above does (verifying this yourself would be a productive exercise), but finishes in a fourth the time when used on a similar string with 1000000 Cs. Be aware, however, that this pattern currently triggers a warning message under -B<-w> saying it C<"matches the null string many times">): +the C pragma or B<-w> switch saying it +C<"matches the null string many times">): -On simple groups, such as the pattern C<(?E [^()]+ )>, a comparable +On simple groups, such as the pattern C<< (?> [^()]+ ) >>, a comparable effect may be achieved by negative look-ahead, as in C<[^()]+ (?! [^()] )>. This was only 4 times slower on a string with 1000000 Cs. @@ -676,7 +674,7 @@ The "grab all you can, and do not give anything back" semantic is desirable in many situations where on the first sight a simple C<()*> looks like the correct solution. Suppose we parse text with comments being delimited by C<#> followed by some optional (horizontal) whitespace. Contrary to -its appearence, C<#[ \t]*> I the correct subexpression to match +its appearance, C<#[ \t]*> I the correct subexpression to match the comment delimiter, because it may "give up" some whitespace if the remainder of the pattern can be made to match that way. The correct answer is either one of these: @@ -911,12 +909,12 @@ then it would take forever--or until you ran out of stack space. A powerful tool for optimizing such beasts is what is known as an "independent group", -which does not backtrack (see Lpattern)>>). Note also that +which does not backtrack (see Lpattern) >>>). Note also that zero-length look-ahead/look-behind assertions will not backtrack to make the tail match, since they are in "logical" context: only whether they match is considered relevant. For an example where side-effects of look-ahead I have influenced the -following match, see Lpattern)>>. +following match, see Lpattern) >>>. =head2 Version 8 Regular Expressions @@ -936,8 +934,10 @@ in C<[]>, which will match any one character from the list. If the first character after the "[" is "^", the class matches any character not in the list. Within a list, the "-" character specifies a range, so that C represents all characters between "a" and "z", -inclusive. If you want "-" itself to be a member of a class, put it -at the start or end of the list, or escape it with a backslash. (The +inclusive. If you want either "-" or "]" itself to be a member of a +class, put it at the start of the list (possibly after a "^"), or +escape it with a backslash. "-" is also taken literally when it is +at the end of the list, just before the closing "]". (The following all specify the same class of three characters: C<[-az]>, C<[az-]>, and C<[a\-z]>. All are different from C<[a-z]>, which specifies a class containing twenty-six characters.) @@ -1162,7 +1162,7 @@ Same as C, C, C respectively. Same as C, C, C respectively. -=item C<(?ES)> +=item C<< (?>S) >> Matches the best match for C and only that. @@ -1177,7 +1177,7 @@ else in the whole regular expression.) For this grouping operator there is no need to describe the ordering, since only whether or not C can match is important. -=item C<(?p{ EXPR })> +=item C<(??{ EXPR })> The ordering is the same as for the regular expression which is the result of EXPR.