I wrote a program to do batch renaming on my mp3s. Tried, rather. 

c:> rename.pl .*\.mp3 1(\d\d.*) 4$1

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What I want is 103_track.mp3 to turn into 403_track.mp3. What I get is a file named 4$1. Thanks in advance. 
my $inputMask = $ARGV[0];
my $regexSearch = $ARGV[1];
my $regexReplace= $ARGV[2];

my @files = <*.*>;

foreach my $file ( @files )
{
    if ( $file =~ /$inputMask/ )
    {
        my $oldname = $file;
        $file =~ s/$regexSearch/$regexReplace/;

        rename($oldname, $file) or die "$oldname to $file failed: $!";
        print "renamed $oldname to $file\n";
    }
}

[download]

In reply to s/// treat rhs as regex by chuckH

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