#!/usr/bin/perl -w
use Audio::Mixer;
use Term::ReadKey;
use Term::Size;

#sudo apt-get install libaudio-mixer-perl libterm-readkey-perl libterm-size-perl

Audio::Mixer::init_mixer();

END { Audio::Mixer::close_mixer(); ReadMode 0; print "\n"; }

sub vol
{
  my @v = (Audio::Mixer::get_cval('vol'),
	   Audio::Mixer::get_cval('pcm'));
  my $n = 0;
  $n += $_ for @v;
  $n/4;
}

sub incvol
{
  my $i = shift;
  my $v = vol();
  Audio::Mixer::set_cval('vol', $i + $v);
  Audio::Mixer::set_cval('pcm', $i + $v);
}

sub dispvol
{
  my $w = Term::Size::chars;
  my $barwidth = $w - 11;

  $|++;
  printf "
 [%-${barwidth}s] (%i%%) 
", 
    '#' x int($barwidth*vol()/100), vol;
}

ReadMode 4;
my $prefix;

dispvol;
while (defined($_ = ReadKey))
{
  if (m/\d/) { $prefix .= $_; }
  elsif (m/[hjkl]/)
  {
    $prefix ||= 2;
    m/[hj]/ && ($prefix *= -1);
    incvol $prefix;
    undef $prefix;
  }
  else { exit }
  dispvol;
}