#!/usr/bin/perl
use strict;
use warnings;
use CGI;
use Data::Dumper;

my $cgi = CGI->new();

my %p = $cgi->Vars;
# if you don't like the \0 delimiter, replace it by your own one; e.g.:
s/\0/[whatever I want]/g for values %p;

print Dumper \%p;

__END__

$ perl T.pl a=1 b=1 b=2 b=3 
$VAR1 = {
          'a' => '1',
          'b' => '1[whatever I want]2[whatever I want]3'
        };