How to validate password with regular expression

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})


Description

* ?= – means apply the assertion formula, meaningless by itself, always work with other combination.
* . – means any characters except new line “\n”
* * – means length can be zero or more
* () – grouping
* (?=.*\d) – \d means digit from 0-9. Only digit is allow here.
* (?=.*[a-z]) – [a-z] means lowercase characters from a to z. Only lowercase characters is allow here.
* (?=.*[A-Z]) – [A-Z] means uppercase characters from A to Z. Only uppercase characters is allow here.
* (?=.*[@#$%]) – [@#$%] means special character “@#$%”. Only special characters “@#$%” is allow here.
* {6,20} – the length of the string, minimum characters is 6, maximum characters is 20.

Whole combination is means, 6 to 20 characters string with at least one digit, one upper case letter, one lower case letter and one special symbol (”@#$%”). This regular expression pattern is very useful to implement a strong and complex password.

P.S The grouping formula order is doesn’t matter.