#! /usr/bin/perl -w

# onchange file ... command
# run command if any of the given files/directories
# change

use strict;
use warnings;
use File::Find;
use Digest::MD5;

my $Command = pop @ARGV;
my $Files = [@ARGV];
my $Last_digest = '';

sub has_changed {
        my $files = shift;
        my $ctx = Digest::MD5->new;
        find(sub {$ctx->add($File::Find::name, (stat($_))[9])}, grep {-e $_} @$files);
        my $digest = $ctx->digest;
        my $has_changed = $digest ne $Last_digest;
        $Last_digest = $digest;
        return($has_changed);
};

while (1) {
        system($Command) if has_changed($Files);
        sleep 1;
};