#!/usr/bin/perl
use strict;
use warnings;
use File::Spec;
use Cache::FileCache ();

unless ( @ARGV ) {
    my $script = (File::Spec->splitpath($0))[2];
    die "$script another_program -and -its -args\n"
      . "caches the output from the command and only prints if it diff
+ers fro"
      . "m the last time $script was run. This allows you to say `$scr
+ipt who"
      . "is -i somedomain.org` and only have output show up when the w
+hois ou"
      . "tput changes\n";
}

my $pid;
my $sleep_count = 0;
do {
    $pid = open KID_TO_READ, "-|", @ARGV;
    unless (defined $pid) {
        warn "cannot fork: $!";
        die "bailing out" if $sleep_count++ > 6;
        sleep 10;
    }
} until defined $pid;

my $self = File::Spec->rel2abs( $0 );
my $cache = Cache::FileCache->new( { namespace => $self } );
my $old = $cache->get( "@ARGV" );
my $new = do { local $/; <KID_TO_READ> };

if ($new ne $old) {
    print $new;
    $cache->set( "@ARGV", $new );
}
close KID_TO_READ or warn "kid exited $?";