#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

sub strip_paren {
   my $input = $_[0];
   our $re;

   $re = qr/
        ( [^()]+ )
        (?: 
          \(
            (
              (?:
               (??{$re})
              )+
            )+
          \)
        )?
       /x;

   my @output = ();
      @output = $input =~ /$re/g;

   return @output;
}

sub print_crud {
   print "\nLine: ", shift, "\n";
   foreach my $line (@_) {
      next if not defined $line;
      print "  '$line'\n";
   }
}

while (<DATA>) {
    chomp;
    print_crud( $_, strip_paren($_));
}
exit;

__DATA__
A
A B
A B C 
(A B) C
A (B) C
A (B C D)
A(B C D)
A (B C D) E
A (B C D)E
A (B C D) (E F G)
A (B C D) (E F G) I
A B (C (D E) (F G)) (H I)
A B (C (D E) (F G)) (H I) J
[download]