#!/usr/bin/perl
use strict;
use warnings;

my %seen;
for my $file (@ARGV) {
    open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $!";
    while (<$fh>) {
        my ($set) = $_ =~ /^(\w+)/;
        powerset($set);
    }
}
sub powerset {
    my $set = shift @_;
    return if $seen{$set}++;
    print "$set\n";
    powerset($_) for subsets($set);
}