Regex for password must contain at least eight characters, at least one number and both lower and uppercase letters and special characters

Question

I want a regular expression to check that:

A password contains at least eight characters, including at least one number and includes both lower and uppercase letter

Answer 1

Not directly answering the question, but does it really have to be a regex?

I used to do lots of Perl, and got used to solving problems with regexes. However, when they get more complicated with all the look-aheads and other quirks, you need to write dozens of unit tests to kill all those little bugs.

Furthermore, a regex is typically a few times slower than an imperative or a functional solution.

For example, the following (not very FP) Scala function solves the original question about three times faster than the regex of the most popular answer. What it does is also so clear that you don't need a unit test at all:

def validatePassword(password: String): Boolean = {
  if (password.length < 8)
    return false

  var lower = false
  var upper = false
  var numbers = false
  var special = false

  password.foreach { c =>
    if (c.isDigit)       numbers = true
    else if (c.isLower)  lower = true
    else if (c.isUpper)  upper = true
    else                 special = true
  }

  lower && upper && numbers && special
}