use strict;
use warnings;

my $Usage = "Usage:  $0  [-f] directory_path\n";

my $force;
if ( @ARGV > 1 and $ARGV[0] eq '-f' ) {
    $force = shift;
}
die $Usage unless ( @ARGV == 1 );

my $dirname = shift;

if ( -e $dirname and ! $force ) {
    die "$dirname exists.  Use '-f' option to delete the existing $dirname\n$Usage";
}
...