On Wed, 2008-12-24 at 11:40 +0530, Amit Saxena wrote: > Hi all, > > I am trying to use recursive regular expression in Perl. > > I am using an example from http://www.perl.com/pub/a/2003/06/06/regexps.html. > > Whenever I try to execute the program, it hangs and I have to do a CNTRL-C > to break it. > > Please let me know where I am wrong. > > *# cat t_r.pl* > #! /usr/bin/perl > > use warnings; > use strict; > > my $paren = qr/ \( [^)]+ \) /x; > > "Some (parenthesized) text" =~ /($paren)/; > print $1; # parenthesized > > $paren = qr/ > \( > ( > [^()]+ # Not parens > | > (??{ $paren }) # Another balanced group (not interpolated yet) > )+? > \) > /x; > > print "\n"; > > "Some (parenthesised and (gratuitously) sub-parenthesised text" =~ > /($paren)/; > print $1; # parenthesized > > print "\n"; > > *# perl t_r.pl* > (parenthesized) > <<Control-Break>> > *# perl -v* > > This is perl, v5.8.5 built for i386-linux-thread-multi > > Copyright 1987-2004, Larry Wall > > Perl may be copied only under the terms of either the Artistic License or > the > GNU General Public License, which may be found in the Perl 5 source kit. > > Complete documentation for Perl, including FAQ lists, should be found on > this system using `man perl' or `perldoc perl'. If you have access to the > Internet, point your browser at http://www.perl.com/, the Perl Home Page. > > *#*
I don't think you're doing anything wrong. I think the guy who wrote the web page didn't test his regex with a string with unbalanced parenthesis. Try: "Some (parenthesised and (gratuitously) sub-parenthesised) text" =~ /($paren)/; You cannot parse unbound-nested contexts with regular expressions. You need a finite-state automation (FSA) with a push-down stack. -- Just my 0.00000002 million dollars worth, Shawn Believe in the Gods but row away from the rocks. -- ancient Hindu proverb -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
