I have to do stuff like this fairly often with a bunch of different format files so I just keep this around as a generic framework. I modify the regex statements, delimiter and number of fields as necessary but it's pretty much the same program every time.

Here's what I use - lifted almost completely from various posts here on PM...

#!/usr/bin/perl

use warnings;
use strict;

open INFILE, "< $ARGV[0]"
  or die "Could not open file $ARGV[0]: $!";

until(eof INFILE) {

    my $fn = $ARGV[0];

    open OUTFILE, "> $fn.filtered"
        or die "Could not open file $fn.filtered $!";

    while(<INFILE>) {

        my @line = split /\t/;

        $line[0] =~ s/(.{1,6}).*/$1/;
        $line[3] =~ s/(.{1,6}).*/$1/;
        $line[6] = $line[6]."\n";

        $_ = join("\t", $line[0], $line[1], $line[2], $line[3], $line[
+4], $line[5], $line[6]);

        print OUTFILE;

    }


}
[download]

BTW, this code processed an 8 million line/385 mb file in about 33 minutes the other day on my old, anemic Sun Ultra 5 workstation. No brownouts, no sweat. System load never got above 1.05.

Jack