#!perl
use warnings;
use strict;
use CGI;
my $string = join ';',('elem1=comment1','elem1_drp=cause1',
'elem2=comment2','elem2_drp=cause2',
'elem3=comment3','elem3_drp=cause3');

my $q = CGI->new($string);
for my $k ( sort $q->param ) {
  if ($k =~ /(.+)_drp$/){
    print join'|', $q->param( $1 ),$q->param( $k )."\n";
  }
}