use strict; use warnings; my %pairs; while () { my @names = split; for my $first (0..$#names - 1) { for my $second ($first + 1 .. $#names) { my $p = join '_', @names[$first, $second]; $pairs{$p}++; } } } while (my ($k, $v) = each %pairs) { print "$k: $v\n"; } __DATA__ tomD gly4 phil aesG tomD gly4 phil aesG phil aesG tomD gly4