#!/usr/bin/perl -w
use strict;

die "Usage fileReference File2Check >outfile" if @ARGV != 2;
my ($fileRef, $file2Check) = @ARGV;
open (REF, "<$fileRef")    || die "unable to open $fileRef";
open (CHK, "<$file2Check") || die "unable to open $file2Check";

my %seen = map{chomp; $_ => 1 }(<REF>);

print grep { my $token = (split /,/,$_)[0];
             !$seen{$token}
           }(<CHK>);

__END__
fileref:
ab
gh
kl
mn
op

file2check:
ab, 1234
cd, 2343
ef, 1253
gh, 4543
ij, 2343
kl, 2453
mn, 4753

output:
cd, 2343
ef, 1253
ij, 2343