use strict;
use File::Find;

my $cod    = shift or die 'some error message';
my $dbpath = '/path/to/somewhere';
my @files;

@ARGV = '.' unless @ARGV;

find sub {
   push(@files, $_) if /\.mp3\z/;
}, @ARGV;

open(DB, ">$dbpath/$cod.txt") || die $!;

print DB map { s/\.mp3\z/\n/; $_ } sort @files;