Hackery

Currency On-Screen Display

Wed 10 Jun 2009

Here's a quick hack demonstrating a nice juxtaposition between the power of a CPAN module - in this case Christopher Laco's Finance::Currency::Convert::WebserviceX - and the elegance and utility of the little known osd_cat, putting together a desktop currency rates widget in a handful of lines:

#!/usr/bin/perl

use strict;
use IO::File;
use Finance::Currency::Convert::WebserviceX;

# Configuration
my @currencies = map { uc } @ARGV || qw(USD GBP);
my $base_currency = 'AUD';
my $refresh = 300;   # seconds
my $font = '9x15bold';
# X colours: http://sedition.com/perl/rgb.html
my $colour = 'goldenrod3';
my $align = 'right';
my $pos = 'top';
my $offset = 25;

my $lines = scalar @currencies;
my $osd_refresh = $refresh + 1;
my $osd = IO::File->new(
  "|osd_cat -l $lines -d $osd_refresh -c '$colour' -f $font -p $pos -A $align -o $offset"
) or die "can't open to osd_cat $!";
$osd->autoflush(1);
local $SIG{PIPE} = sub { die "pipe failed: $!" };

my $cc = Finance::Currency::Convert::WebserviceX->new;

while (1) {
  my $output = '';
  $output .= "$_ " . $cc->convert(1, $base_currency, $_) . "\n" for @currencies;
  $osd->print($output);
  sleep $refresh;
}

Most of this is just housekeeping around splitting out various osd_cat options for tweaking, and allowing the set of currencies to display to be passed in as arguments. I haven't bothered setting up any option handling in order to keep the example short, but that would be straightforward.

To use, you just run from the command line in the background:

./currency_osd &

and it shows up in the top right corner of your screen, like so:

Tweak to taste, of course.