Why not:

use strict;
use IO::File;

use constant INDEX_FILE => './index.html';

my $fh = IO::File->new(INDEX_FILE)
  or die INDEX_FILE, ":$!";

while(<$fh>) {
  if(m!<a href=["']([^"']+)!i) {
    my $mp3 = $1;

    system('mpg123', "-p none -b 500 -q $mp3")
      if($mp3 =~ m!$ARGV[0]!i);
  }
}
[download]

Or, even better (not perl, and uses filesystem instead):

find . -type f -iname '*.mp3' | grep "pattern here" | xargs mpg123 -p 
+none -b 500 -q
[download]

have fun.