You can easily replace `ls` with glob, `basename` with File::Basename and `pwd` with Cwd::getcwd. Then your script would also work elsewhere.

As a note on your coding style, Perl is not the shell, so there is little need to quote parameters when passing them to functions.

chdir( "$dir" );
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is better written as

chdir( $dir );
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You can use the /i switch to make your regular expressions match case insensitively, so /\.mp3$/i will also match .Mp3.

It also assumes you are willing to edit the script every time you want to run it on some different directory (other than "/steeler/mp3", which doesn't exist on most "unixy-type" systems ;)

And it assumes that if the directory contains any mp3 file, then it contains nothing but mp3 files -- all files get listed in your "m3u" file (including the m3u file, if the script has been run previously on that path).

And it assumes that there will never be a problem with opening "m3u" files for output, or that you don't care when open fails.

There's no need to make any of these assumptions (and no need for chdir):

#!/usr/bin/perl

use strict;
use warnings;
use File::Find::Rule;
use File::Spec;

die "Usage: $0 path/to/search\n" unless ( @ARGV == 1 and -d $ARGV[0] )
+;

my @dirs = File::Find::Rule->directory()->in( $ARGV[0] )
    or die "Can't find anything in $ARGV[0]\n";

for my $dir ( @dirs ) {
    my @mp3s = File::Find::Rule->maxdepth(1)->file()->name("*.[Mm][Pp]
+3")->in($dir);
    if ( @mp3s ) {
        ( my $m3u = ( File::Spec->splitdir( $dir ))[-1] ) =~ s/[\s.']+
+//g;
        if ( open( M3U, ">", "$dir/$m3u.m3u" )) {
            print M3U "$_\n" for ( @mp3s );
            close M3U;
            warn sprintf( "%d mp3s listed in %s\n", scalar @mp3s, "$di
+r/$m3u.m3u" );
        }
        else {
            warn "Unable to create $dir/$m3u.m3u : $!\n";
        }
    }
}
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I find it peculiar that the file system is scanned twice. The following avoids that:

#!/usr/bin/perl

use strict;
use warnings;

use File::Find::Rule qw( );
use Path::Class      qw( file );

die "Usage: $0 path/to/search\n"
   if @ARGV != 1 || !-d $ARGV[0];

my @scan = File::Find::Rule
   ->name(qr/\.mp3\z/i)
   #->file
   ->in( $ARGV[0] );

my $last_dir = '';
my $fh;

for (@scan) {
   my $file = file($_);
   my $dir = $file->dir;

   if ($dir ne $last_dir) {
      $dir = $last_dir;

      my $m3u = $dir->dir_list(-1);
      $m3u =~ s/[\s.']+//g;
      $m3u = $dir->file("$m3u.m3u");

      open($fh, '>', $m3u)
         or warn("Unable to create \"$m3u\": $!\n");
   }

   print($fh "$_\n");
}
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Untested.

Note that this (and previous solutions) will probably create an m3u named "..m3u" if you pass "." for argument and that directory contains mp3s. This can be solved by changing
->in( $ARGV[0] )
to
->in( dir($ARGV[0])->absolute )
(Don't forget to import dir.)

(Should have been a reply to the OP. The OP was notified.)