once

#!/usr/bin/env perl

# Print stdin once if it has changed since last time

use strict;
use warnings;
no warnings 'uninitialized';

my $file = $ARGV[0] || die "Specify cache file";
$file = "/tmp/once_" . $ENV{USER} . "_" . $file;

undef $/;

my $data = <STDIN>;
my $old_data;

if (-e $file) {
    open(my $fileh, "<", $file) || die $!;
    $old_data = <$fileh>;
}

exit 0 if $data eq $old_data;

print $data;

open(my $fileh, ">", $file)
    or die "cannot open > $file: $!";
print $fileh $data;