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

open (FH,"<prev_file") or die;
my @prev = <FH>;
close FH;

open (FH,"<current") or die;
my @current = <FH>;
close FH;

foreach (0 .. $#prev) {
    print $prev[$_] if ($prev[$_] ne $current[$_]);
}

##</code><code>##

grep> cd pub
grep> more beer