for f in *; do
g=`expr "xxx$f" : 'xxx\(.*\)' | tr '[A-Z]' '[a-z]'`
mv "$f" "$g"
done

#!/usr/bin/perl -w
use strict;
# Open 'find' process to list files recursively with paths
open(FIND, "find |");
while() {
        chomp;
        next if $_ eq $0;        # Don't rename ourself
        rename($_, lc($_));
        }
close(FIND);