Note that crypt is intended to be a one-way function, much like breaking eggs to make an omelette. There is no (known) corresponding decrypt function. As a result, this function isn't all that useful for cryptography. (For that, see your nearby CPAN mirror.)

Here's an example that makes sure that whoever runs this program knows their own password:

    $pwd = (getpwuid($<))[1];
    $salt = substr($pwd, 0, 2);

    system "stty -echo";
    print "Password: ";
    chop($word = <STDIN>);
    print "\n";
    system "stty echo";

    if (crypt($word, $salt) ne $pwd) {
        die "Sorry...\n";
    } else {
        print "ok\n";
    }

Of course, typing in your own password to whomever asks you for it is unwise.