#!/usr/bin/perl

use strict;
use warnings;

chomp (my @lines = <DATA>);
for my $i (0 .. $#lines) {
    (my $re = $lines[$i]) =~ s/_/|/g; # create $re outside the inner loop
    for my $j ($i + 1 .. $#lines) {
        my $count = () = $lines[$j] =~ /$re/g;
        if ($count >= 2) {
            print "$lines[$i] and $lines[$j]\n";
        }
    }
}
__DATA__
one_two
one_three_two
three_one
one_four
four_three_one