in reply to pattern matching nested { }'s

Using Regexp::Common you should do this quite easily.

#!/usr/bin/perl -w
use strict;
use Regexp::Common;

my $text = <<TEXT;
   onValidate
   {
    stuff in here
    {
       other stuff
    }
   }
   keep this
   {
       remove this {and {this}}
   }
TEXT

$text =~ s/$RE{balanced}{-parens=>'{}'}//g;

print $text;

[download]

It will print:

   onValidate

   keep this

Update [1] If you'd rather do this without a module, you can try this regular expression:

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

[download]
(I am not a RegEx guru. I got it by just printing $RE{balanced}{-parens=>'{}'} and adjusting it a bit.)

Update [2] And to explain how all this works, here goes:

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new($re)->explain;

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The regular expression:

(?-imsx:(?:\{(?:(?>[^\{\}]+)|(??{$re}))*\}))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    \{                       '{'
----------------------------------------------------------------------
    (?:                      group, but do not capture (0 or more
                             times (matching the most amount
                             possible)):
----------------------------------------------------------------------
      (?>                      match (and do not backtrack
                               afterwards):
----------------------------------------------------------------------
        [^\{\}]+                 any character except: '\{', '\}' (1
                                 or more times (matching the most
                                 amount possible))
----------------------------------------------------------------------
      )                        end of look-ahead
----------------------------------------------------------------------
     |                        OR
----------------------------------------------------------------------
      (??{$re})                run this block of Perl code (that
                               isn't interpolated until RIGHT NOW)
----------------------------------------------------------------------
    )*                       end of grouping
----------------------------------------------------------------------
    \}                       '}'
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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Replies are listed 'Best First'.
Re: Re: pattern matching nested { }'s
by Gerard (Pilgrim) on Mar 02, 2004 at 10:28 UTC
    Thanks for your reply. I think I was a little unclear in my original post. Only the { } immediately after onValidate should match. For example: 
     
   onValidate
   {
    stuff in here
    {
       other stuff
    }
   }

    [download]
    should all be removed and 
       keep this
   {
       remove this {and {this}}
   }

    [download]
    should all be kept.

    Thanks, Gerard.
[reply]
[d/l]
[select]

      Well, in that case, just say it to your replacement command:

      $text =~ s/(onValidate)\s*$re/$1/g;

# or even $text =~ s/(?<=onValidate)\s*$re//g;

print $text;

      [download]

      It gives:

         onValidate
   keep this
   {
       remove this {and {this}}
   }
[reply]
[d/l]

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