#!/usr/local/bin/perl -w use strict; open(FILE, "<dav94t325m") || die "Cannot open file\n"; my $start = $ARGV[0] || 0; foreach (0 .. $start) { <FILE> || die "unexpected end of file\n"; }; my ($num, $sum) = (0, 0); my $l = undef; while (<FILE>) { $num = (split /:/)[2]; $sum += $num; $l = $num unless defined $l; } close(FILE); print $sum / $l - 0.5, "\n";