sub scandir {
    my $dir=shift;
    my $test=join '|', map quotemeta, @_;
    chdir $dir;
    for (glob '*') {
        next unless /^($test)(.*)/;
        my $new="$1D$2";
        print "`$_' => `$new'\n";
        if (-e $new) {
            warn "Warning: `$new' exists\n";
            # or do something more complex...
            next;
        } else {
            rename $_, $new or die "Can't rename to `$new': $!\n";
        }
    }
}