#!/usr/bin/perl
use strict; use warnings;
use List::Util qw(sum);

my @array = ();
while (<DATA>) {
   next if /start/;
   chomp;
   my (undef,undef,undef,$col4,undef) = split (/\s*/, $_,5);
   push (@array, $col4);
}

my $sum = sum(@array);    print $sum,"\/";
my $n = scalar(@array);   print $n,"\n";
print "average = ", $sum/$n,"\n";

__DATA__
chr    start    end    length foo
e r t 6 r
4 A 6 4 f
4 3 4 5 f
L 0 L 2 f
0 0 0 1 0
3 4 5 6 7