Script To Rename && Convert Music Files

mistersnorfles · 08-18-2007, 10:18 PM

I am just starting to learn Perl and I am trying to write a script that will go through all of my music files and do the following:

1) Change all spaces in file names into underscores.
2) Change all uppercase letters file names into lowercase.
3) Find all .m4a files in my music directory && convert them into .mp3 format
4) Remove the old .m4a files.

I understand there is probably software out there, already designed to do this, but I am just writing this as a programming exercise to learn better.

Below is what I have come up with so far. Bear with me if there is something stupid I've written here -- I'm still learning.

Anyhow, I am worried about running any scripts that I have written that rename or remove files, because I am not sure how things are interpolated in the backticks before running the command (backticks being the little tilted single-quote looking things around the command to be run...), and don't want a weird character to be fed into the regex, and have it start wiping out files I don't want it to.

Here is what I have so far:

Code:

#!/usr/bin/perl -w
use File::Find;

$music_dir="/mnt/storage/music";

find(\&Wanted, $music_dir);

sub Wanted{
	$_ eq "." and next;
	$_ eq ".." and next;

	my $new_filename = $_;	
	
	#Change all letters to lowercase
	$new_filename =~ s/(\w+)/\L$1/g;

	#Change whitespace to underscore
	$new_filename =~ s/(\s+)/_/g;
	rename $File::Find::name, "$File::Find::dir/$new_filename";
	
	#Then convert it to the proper format && remove the old copy.

	if ($new_filename =~ /(\w+)[.]{1}m4a$/){
	
          `faad $File::Find:dir/$new_filename`
	     or die "Couldn't transcode $File::Find::dir/$new_filename from .m4a to .wav: $!";

	  `lame -m j $new_filename $1.mp3`
	     or die "Couldn't transcode $File::Find::dir/$new_filename from .wav to .mp3: $!";

	   `rm $File::Find::dir/$new_filename`
	     or die "Couldn't remove $File::Find::dir/$new_filename: $!";

	   `rm $File::Find::dir/$1.wav`
	     or die "Couldn't remove $File::Find::dir/$new_filename: $!";
	}
}

Does this look like it will work? I am especially worried about my regular expressions. Do they look sensible? Anybody have any suggestions on how to make it work better?

Also, if anyone has some good documentation on what goes on inside those backticks, I'd love to hear all about it...

Thanks,
Mr. Snorfles

rickh · 08-19-2007, 03:39 PM

http://www.linuxquestions.org/questi...d.php?t=555911

That thread addresses some of your questions. You situation is a little different because you're dealing with m4a files, but it looks to me like you have that under control.

The "backtick" function has been deprecated, and (for me) using the new format makes it easier to understand. Replace the backtics with $() ... like this: $ echo $(uname -r)

mistersnorfles · 08-19-2007, 06:25 PM

Thanks a bunch rickh, I'd never heard of the $() function. I'll look into that...

Thanks for the help!

--Mr. Snorfles

chrism01 · 08-19-2007, 08:02 PM

Instread of a regex, I'd used the lc() fn to convert case.
http://perldoc.perl.org/functions/lc.html
Also, mandate
use locale;
at the top of your prog to deal with any accented chars (even if you don't have any, it's good practice)
Also,
use strict;
forces declarations and traps some other possible errors. Again, it's best practice to use that and the "-w" switch together. They do different checks.
To do a test compile without running prog do
perl -wc yourprog.pl
which will just do a test compile and syntax check.
The other thing is to comment out the rm cmds until you've tested the rest.
Use the unlink() fn instead of rm.
http://perldoc.perl.org/functions/unlink.html

HTH

mistersnorfles · 08-19-2007, 08:34 PM

Yeah I figured there was a lowercase function, but I just didn't know what it was called. I agree, lc() will definitely be an easier way to do this. Thanks Chris.

By the way, as fan as using unlink() vs rm, what are the benefits?

Same with $() vs `command` -- why is the former the better choice?

Thanks for the help folks.

--Mr. Snorfles

chrism01 · 08-19-2007, 08:47 PM

unlink - give it a scalar containing full path, or just filename if perl prog is in same dir as file to remove.
If you don't require to trap/gather the output from external cmds, you can use system() http://perldoc.perl.org/functions/system.html
The doc page explains this more fully.

Personally, I'd use something like the following instead of File::Find:

Code:

opendir(DIR, $dirname) or die "can't opendir $dirname: $!";
while (defined($file = readdir(DIR))) 
{
    next if $file =~ /^\.\.?$/;     # skip . and ..
    # do something with "$dirname/$file"
}    
closedir(DIR);

but TMTOWTDI, YMMV

mistersnorfles · 08-19-2007, 09:48 PM

Thanks again for all the help. I made the suggested modifications --except for $() which I couldn't figure out -- and everything worked wonderfully. Here was the script I ended up running:

Code:

#!/usr/bin/perl -w
use File::Find;
use locale;
use strict;

my $music_dir="/mnt/storage/music";

find(\&Wanted, $music_dir);

sub Wanted{
	$_ eq "." and next;
	$_ eq ".." and next;

	my $new_filename = $_;	
	
	#Change all letters to lowercase
	$new_filename=lc($new_filename);

	#Change whitespace to underscore
	$new_filename =~ s/(\s+)/_/g;
	rename( $File::Find::name, "$File::Find::dir/$new_filename");
	
	#Then convert it to the proper format && remove the old copy.
	if ($new_filename =~ /([\w',]+)[.]{1}m4a$/){
	  my $filename_no_ext = $1;
          
         (system("faad", "$File::Find::dir/$new_filename") or $new_filename =~ s/m4a$/wav/)
           or die "Couldn't transcode $File::Find::dir/$new_filename from .m4a to .wav: $!";
		   
	  system("lame", "-m","j", "$new_filename", "$filename_no_ext.mp3")
	   and die "Couldn't transcode $File::Find::dir/$new_filename from .wav to .mp3: $!";
		
	  unlink("$File::Find::dir/$new_filename")
           or die "Couldn't remove $File::Find::dir/$new_filename: $!";
   	  unlink("$File::Find::dir/$filename_no_ext.m4a")
           or die "Couldn't remove $File::Find::dir/$new_filename: $!";
	}
}

Went off without a hitch...

Thanks,
Mr. Snorfles

chrism01 · 08-20-2007, 08:03 PM

I assume this
(system
is a typo?
Also,
and die "
should be 'or die' ?