sub process_files {
    my ($function, $parm, $message, $extension, @list) = @_;
    ...

##</code><code>##

sub process_files {
    my ( $SubArgs ) = @_;

    my $function  = $SubArgs->{ function }
    my $message   = $SubArgs->{ message }
    my $parm      = $SubArgs->{ parm } || "";  #  If no parameter, default to "".
    my $extension = $SubArgs->{ extension };
    my @list      = @{ $SubArgs->{ list } };
    ...

##</code><code>##

    foreach my $file (@list) {
        my $Newfile = substr($file, 0, 2);
        $Newfile = $Newfile . $extension;
        print "($function) $message $file to $Newfile\n";

        @args = ("$function", "$parm", "$Newfile", "$file");
        system(@args) == 0 or die "system @args failed: $?";

        push @returnlist, $Newfile;
    }

##</code><code>##

# rename files to 01.mp3, 02.mp3, etc.
my @mp3list = 
   process_files( { function => "mv", message => "renaming", extension => "\.mp3", list => @list } );
 
# call mpg123 to convert .mp3 to .wav
my @wavlist = 
   process_files( { function => "mpg123", param => "-qw", message => "converting", extension => "\.wav", list => @mp3list } );
 
# call sox to convert each .wav to .cdr
my @cdrlist = 
   process_files( { function => "sox", message => "converting", extension => "\.cdr", list => @wavlist } );