PHP script to create bcrypt hash password

bcrypt.php

#!/usr/bin/php
<?php

function create_salt(){
	$salt_source = "./ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

    $num = strlen($salt_source)-1;
    $salt = "";
    for($i=0; $i<22; $i++){
        $index = mt_rand(0, $num);
        $salt .= $salt_source[$index];
    }
    return $salt;
}

if ( count($argv) != 2 ){
	$script = basename(__FILE__);
	echo "Usage: $script password\n";
	exit;
}

$password = $argv[1];
$salt = create_salt();
$hash = crypt($password, '$2a$10$'.$salt);
print $hash . "\n";