Something like this?

#!/usr/bin/perl

use strict;
use warnings;

my ($cur_rec, $prev_rec, $line) = ("", "", "");

while ($line = <STDIN>) {
    $cur_rec = join("", (split(/\|/, $line))[1..4]);
    if ($cur_rec ne $prev_rec) {
        print $line;
    }
    $prev_rec = $cur_rec;
}
[download]

With this script, you can process files of arbitrary length, because the while file isn't stuffed into a hash. It processes from standard input to standard output, thus you can give it any file you like, instead of hardcoding filenames in the script. It's a lot more efficient than opening, writing, and closing the same file over and over in a loop.

Arjen