Use the File::Copy Module like so:

#!/usr/bin/perl -w

use strict;
use File::Copy;

my $current_filename = "foo";
my $new_filename     = "foo" . localtime;

move($current_filename, $new_filename)
        or die "Couldn't move $current_filename to $new_filename: $!\n
+";
[download]

Be aware that this code creates a file with spaces in the filename, which is generally considered not a nice thing (tm).
hope this helps
davis