Hi fionbarr,

Here is one possible way:

use strict;
my $n = 2;
my $cnt;
my $sum;

while(<>) {
    chomp;
    $cnt++;
    my (undef, $v) = split(/\|/);
    $sum += $v;
    print "cnt: $cnt v: $v sum: $sum\n";
    if (($cnt % $n) == 0) {
        print "avg: " . $sum / $n . "\n";;
        $sum = 0 ;
    }
}
[download]

You can use 'perldoc -f glob' or shell commands to redirect all the input data to stdin.