#!/usr/bin/env perl -l

use strict;
use warnings;

my @vars = ('abc,d', 'abcd', 'a,b,c,d');

for my $var (@vars) {
    print "var = '$var'";
    print 'm/,/: ', $var =~ /,/ ? 'not matches' : 'matches';
    print 'y/,/,/: ', $var =~ y/,/,/ ? 'not matches' : 'matches';
    print '! m/,/: ', $var !~ /,/ ? 'matches' : 'not matches';
    print '! y/,/,/: ', $var !~ y/,/,/ ? 'matches' : 'not matches';
}

##</code><code>##

var = 'abc,d'
m/,/: not matches
y/,/,/: not matches
! m/,/: not matches
! y/,/,/: not matches
var = 'abcd'
m/,/: matches
y/,/,/: matches
! m/,/: matches
! y/,/,/: matches
var = 'a,b,c,d'
m/,/: not matches
y/,/,/: not matches
! m/,/: not matches
! y/,/,/: not matches