#!/usr/bin/perl

use strict;
use warnings;

my $maxfile = "/sys/class/leds/tpacpi\:\:kbd_backlight/max_brightness";
my $current = "/sys/class/leds/tpacpi\:\:kbd_backlight/brightness";

my ($max, $now, $new);
if (open(my $m, '<', $maxfile)) {
    $max = readline($m);
    chomp $max;
    close($m);
} else {
    print "Failed to read $maxfile\n";
    exit;
}
print STDERR "max = $max\n";

if (open(my $c, '<', $current)) {
    $now = readline($c);
    chomp $now;
    close($c);
} else {
    print "Failed to read $current\n";
    exit;
}
print STDERR "now = $now\n";

if (open(my $fh, '>', $current)) {
    $new = (($now+1) % ($max+1));
    chomp $new;
    print $fh $new;
    close($fh);
} else {
    print "Failed to write $current\n";
    exit;
}
print STDERR "new = $new\n";