X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfaq6.pod;h=c4512e695afb7159754713bcb9f2cc686a24fbe1;hb=510179aa6f5aa7ad3c9e95a67b4958c9aa11a67f;hp=5100c351e8cf769f5788c965a0435b10242b8153;hpb=0e06870bf080a38cda51c06c6612359afc2334e1;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlfaq6.pod b/pod/perlfaq6.pod index 5100c35..c4512e6 100644 --- a/pod/perlfaq6.pod +++ b/pod/perlfaq6.pod @@ -1,6 +1,6 @@ =head1 NAME -perlfaq6 - Regexes ($Revision: 1.27 $, $Date: 1999/05/23 16:08:30 $) +perlfaq6 - Regular Expressions ($Revision: 1.8 $, $Date: 2002/01/31 04:27:55 $) =head1 DESCRIPTION @@ -115,7 +115,7 @@ Here's code that finds everything between START and END in a paragraph: undef $/; # read in whole file, not just one line or paragraph while ( <> ) { - while ( /START(.*?)END/sm ) { # /s makes . cross line boundaries + while ( /START(.*?)END/sgm ) { # /s makes . cross line boundaries print "$1\n"; } } @@ -186,7 +186,7 @@ properties of bitwise xor on ASCII strings. $old = 'test'; $new = 'success'; - s{(\Q$old\E} + s{(\Q$old\E)} { uc $new | (uc $1 ^ $1) . (uc(substr $1, -1) ^ substr $1, -1) x (length($new) - length $1) @@ -194,7 +194,7 @@ properties of bitwise xor on ASCII strings. print; -And here it is as a subroutine, modelled after the above: +And here it is as a subroutine, modeled after the above: sub preserve_case($$) { my ($old, $new) = @_; @@ -212,6 +212,21 @@ This prints: this is a SUcCESS case +As an alternative, to keep the case of the replacement word if it is +longer than the original, you can use this code, by Jeff Pinyan: + + sub preserve_case { + my ($from, $to) = @_; + my ($lf, $lt) = map length, @_; + + if ($lt < $lf) { $from = substr $from, 0, $lt } + else { $from .= substr $to, $lf } + + return uc $to | ($from ^ uc $from); + } + +This changes the sentence to "this is a SUcCess case." + Just to show that C programmers can write C in any programming language, if you prefer a more C-like solution, the following script makes the substitution have the same case, letter by letter, as the original. @@ -368,20 +383,30 @@ A slight modification also removes C++ comments: =head2 Can I use Perl regular expressions to match balanced text? -Although Perl regular expressions are more powerful than "mathematical" -regular expressions because they feature conveniences like backreferences -(C<\1> and its ilk), they still aren't powerful enough--with -the possible exception of bizarre and experimental features in the -development-track releases of Perl. You still need to use non-regex -techniques to parse balanced text, such as the text enclosed between -matching parentheses or braces, for example. +Historically, Perl regular expressions were not capable of matching +balanced text. As of more recent versions of perl including 5.6.1 +experimental features have been added that make it possible to do this. +Look at the documentation for the (??{ }) construct in recent perlre manual +pages to see an example of matching balanced parentheses. Be sure to take +special notice of the warnings present in the manual before making use +of this feature. + +CPAN contains many modules that can be useful for matching text +depending on the context. Damian Conway provides some useful +patterns in Regexp::Common. The module Text::Balanced provides a +general solution to this problem. + +One of the common applications of balanced text matching is working +with XML and HTML. There are many modules available that support +these needs. Two examples are HTML::Parser and XML::Parser. There +are many others. An elaborate subroutine (for 7-bit ASCII only) to pull out balanced and possibly nested single chars, like C<`> and C<'>, C<{> and C<}>, or C<(> and C<)> can be found in -http://www.perl.com/CPAN/authors/id/TOMC/scripts/pull_quotes.gz . +http://www.cpan.org/authors/id/TOMC/scripts/pull_quotes.gz . -The C::Scan module from CPAN contains such subs for internal use, +The C::Scan module from CPAN also contains such subs for internal use, but they are undocumented. =head2 What does it mean that regexes are greedy? How can I get around it? @@ -616,11 +641,20 @@ programming language, you insensitive scoundrel! =head2 How can I match strings with multibyte characters? -This is hard, and there's no good way. Perl does not directly support -wide characters. It pretends that a byte and a character are -synonymous. The following set of approaches was offered by Jeffrey -Friedl, whose article in issue #5 of The Perl Journal talks about this -very matter. +Starting from Perl 5.6 Perl has had some level of multibyte character +support. Perl 5.8 or later is recommended. Supported multibyte +character repertoires include Unicode, and legacy encodings +through the Encode module. See L, L, +and L. + +If you are stuck with older Perls, you can do Unicode with the +C module, and character conversions using the +C and C modules. If you are using +Japanese encodings, you might try using the jperl 5.005_03. + +Finally, the following set of approaches was offered by Jeffrey +Friedl, whose article in issue #5 of The Perl Journal talks about +this very matter. Let's suppose you have some weird Martian encoding where pairs of ASCII uppercase letters encode single Martian letters (i.e. the two @@ -694,15 +728,11 @@ in L. =head1 AUTHOR AND COPYRIGHT -Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. +Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. All rights reserved. -When included as part of the Standard Version of Perl, or as part of -its complete documentation whether printed or otherwise, this work -may be distributed only under the terms of Perl's Artistic License. -Any distribution of this file or derivatives thereof I -of that package require that special arrangements be made with -copyright holder. +This documentation is free; you can redistribute it and/or modify it +under the same terms as Perl itself. Irrespective of its distribution, all code examples in this file are hereby placed into the public domain. You are permitted and