Matching nested balanced delimiters with regular expressions is a hard thing to do. Actually, with true regular expressions, it is impossible. Even when backreferences are added, it's still impossible.

However, perl5.6 adds experimental features to the regular expression syntax which actually make it possible to match nested delimiters with a single (but complicated :) regular expression. I used the example from perlre from perl5.6 for matching balanced parentheses and came up with this code: 

#!/usr/local/bin/perl

require 5.006;

my $braces;
$braces = qr/(\{(?:(?>[^\{\}]+)|(??{$braces}))*\})/;

sub extract_braces {
  my($str, $level) = @_;
  while ($str =~ m!$braces!g) {
    my $inside = $1;
    print "\t" x $level, $inside, "\n";
    $inside =~ s/\{(.*)\}/$1/;
    extract_braces($inside, $level + 1);
  }
}

my $str = '0a { 1a { 1.1a } 1b { 1.2a    } 1c { 1.3a { 1.3.1a } 1.3b }
+  } 0b { 2a { 2.1a}  } 0c';

extract_braces($str, 0);

__END__

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The experimental regex features used here are (??{}) for postponed evaluation, and (?>) for a non-backtracking match.

In reply to Re: Braces by chipmunk
in thread Braces by sangam1

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