What are good regular expressions?

Question

I have worked for 5 years mainly in java desktop applications accessing Oracle databases and I have never used regular expressions. Now I enter Stack Overflow and I see a lot of

Answer 1

Validating strong passwords:

This one will validate a password with a length of 5 to 10 alphanumerical characters, with at least one upper case, one lower case and one digit:

^(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])[a-zA-Z0-9]{5,10}$