How can I validate a password based on my rules?

Question

I have three rules:

• at least 6 characters
• it should be containing both digit(s) and letter(s)
• signs are acceptable like $, @, ^, &, * etc ...

How can I do that?

Here is what I've tried so far:

if ( preg_match($password, "/([0-9]|[a-zA-Z]){6,}/") ) {
    // password is valid
} else {
    // password isn't valid
}

Note1: being capital or lowercase letters doesn't matter.

Note2: starting with whatever doesn't matter.

---

Here is some acceptable examples:

urj2fr
948ff4k
#gk4%rg45
f9493^#0
kf94k39f43

Here is some unacceptable examples:

frki5       // length problem
gerkewkgr%  // lack of digit problem