Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I need to extract a text in between nested paranthesis, and I would like to have the text in between the outermost one. For eg., if the text is given as <code start>I am (giving this (text to (tell you) that this) will give) you the result.<code end> In this case, I need the phrase, (giving this (text to (tell you) that this) will give) This should hold for any number of nested paranthesis. Is there a way to achieve this using Regular Expressions? Or is it the conventional way that is best suited for this? Is there a function which can give the matching paranthesis locations in a given string? As I am a beginner to Regular Expressions of Perl, a code snippet would be of immense help to me.

Replies are listed 'Best First'.
Re: RegEx for Matching paranthesis
by larsen (Parson) on Feb 17, 2004 at 14:38 UTC
    Perl is nice: you can solve your problem remaining a beginner in Regexp :)) (just kidding): take a look at Text::Balanced, maybe it can help you.
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Re: RegEx for Matching paranthesis
by Roger (Parson) on Feb 17, 2004 at 15:21 UTC
    I would recommend using the CPAN module as suggested by larsen. However I am presenting this solution just for fun... :-)
    use strict;
use warnings;

my $str = 'I am (giving this (text to (tell you) that this) will give)
+ you the result)))';

my $match = '';

{
    local $_ = $str;
    my $n = 0;

    s/([()]|.)/
      if ($1 eq '(') {
            $n++;
            $match .= $1
      } elsif ($1 eq ')') {
            if ($n) {
                $n--;
                $match .= $1
            }
      } else {
            $match .= $1 if $n
      }
    /gex;
}

print "$match\n";

__END__

# output
(giving this (text to (tell you) that this) will give)

    [download]

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[d/l]
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Re: RegEx for Matching paranthesis
by Taulmarill (Deacon) on Feb 17, 2004 at 14:36 UTC
    if you want only the text betwen the most left "(" and the most right ")" then this should do:
    /^[^(]*(.*?)[^)]*$/

    ---edit---

    oh, yes, after
    $text =~ /^[^(]*(.*?)[^)]*$/;
    the snippet you want is in $1.
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[d/l]
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Re: RegEx for Matching paranthesis
by borisz (Canon) on Feb 18, 2004 at 00:48 UTC
    Here is a regex taht match nested braces. 
    
my $match;
$match = qr/(?:\((?:(?>[^\(\)]+)|(??{$match}))*\))/;

if ( $text =~ /($match)/ ) {
  print $1; # text between nested ( and )
}

    [download]
    Boris
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Re: RegEx for Matching paranthesis
by I0 (Priest) on Feb 18, 2004 at 01:49 UTC 
    $_ = qq(For eg., if the text is given as
<code start>I am (giving this (text to (tell you) that this) will give
+) you the result.
<code end> In this case, I need the phrase, (giving this (text to (tel
+l you) that this) will give)
This should hold for any number of nested paranthesis.);
(my $re = $_) =~ s/((\()|(\))|.)/${['(','']}[!$2]\Q$1\E${[')','']}[!$3
+]/gs;
print eval{(/$re/)[0]},"\n";
warn $@ if $@;

    [download]
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Re: RegEx for Matching paranthesis
by eyepopslikeamosquito (Archbishop) on Feb 18, 2004 at 07:53 UTC

    See perlfaq6 "Can I use Perl regular expressions to match balanced text?" but be sure you're looking at a recent version (Perl 5.8 or above) since earlier versions don't mention the excellent Text::Balanced solution.

    It's also discussed in the Perl Cookbook, Recipe 6.17 (Matching Nested Patterns).

    /-\

[reply]

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