#! /usr/bin/perl -w

use strict;
use File::Find;

my $root = shift || '.';

find( sub
    {
      return unless /\.mp3$/ and /[ ']/;

      (my $new = $_) =~ tr/ '/__/;

      if( -e $new ) {
          warn "Can't rename $_ to $new (latter already exists).\n";
      }
      else {
          rename $_, $new or warn "Could not rename $_ to $new: $!\n";
      }
    },
    $root );