Larry Wall's file renamer, slightly modified

rename.pl

#!/usr/bin/perl

use strict;
use warnings;

die "Usage: rename <expression> <files>\n"  unless (@ARGV >= 2);

my $op = eval 'sub { ' . shift . ' }'; # crazily dangerous - type carefully!
die $@ if $@;

for (@ARGV) {
    my $was = $_;

    $op->($_);

    unless($was eq $_) {
        rename($was, $_) or warn "Couldn't rename $was -> $_ - $!\n";
    }
}