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Regular expression to check if password is "8 characters including 1 uppercase letter, 1 special character, alphanumeric characters"


Question

I want a regular expression to check that

a password must be eight characters including one uppercase letter, one special character and alphanumeric characters.

And here is my validation expression which is for eight characters including one uppercase letter, one lowercase letter, and one number or special character.

(?=^.{8,}$)((?=.*\d)|(?=.*\W+))(?![.\n])(?=.*[A-Z])(?=.*[a-z]).*$"

How I can write it for a password that must be eight characters including one uppercase letter, one special character and alphanumeric characters?

2018/02/16
1
102
2/16/2018 6:24:57 PM

Accepted Answer

The regular expression you are after will most likely be huge and a nightmare to maintain especially for people who are not that familiar with regular expressions.

I think it would be easier to break your regex down and do it one bit at a time. It might take a bit more to do, but I am pretty sure that maintaining it and debugging it would be easier. This would also allow you to provide more directed error messages to your users (other than just Invalid Password) which should improve user experience.

From what I am seeing you are pretty fluent in regex, so I would presume that giving you the regular expressions to do what you need would be futile.

Seeing your comment, this is how I would go about it:

  • Must be eight characters Long: You do not need a regex for this. Using the .Length property should be enough.

  • Including one uppercase letter: You can use the [A-Z]+ regular expression. If the string contains at least one upper case letter, this regular expression will yield true.

  • One special character: You can use either the \W which will match any character which is not a letter or a number or else, you can use something like so [[email protected]#] to specify a custom list of special characters. Note though that characters such as $, ^, ( and ) are special characters in the regular expression language, so they need to be escaped like so: \$. So in short, you might use the \W.

  • Alphanumeric characters: Using the \w+ should match any letter and number and underscore.

Take a look at this tutorial for more information.

2015/09/23
132
9/23/2015 9:22:13 AM


So many answers.... all bad!

Regular expressions don't have an AND operator, so it's pretty hard to write a regex that matches valid passwords, when validity is defined by something AND something else AND something else...

But, regular expressions do have an OR operator, so just apply DeMorgan's theorem, and write a regex that matches invalid passwords.

anything with less than 8 characters OR anything with no numbers OR anything with no uppercase OR anything with no special characters

So:

^(.{0,7}|[^0-9]*|[^A-Z]*|[a-zA-Z0-9]*)$

If anything matches that, then it's an invalid password.

2015/11/08

The answer is to not use a regular expression. This is sets and counting.

Regular expressions are about order.

In your life as a programmer you will asked to do many things that do not make sense. Learn to dig a level deeper. Learn when the question is wrong.

The question (if it mentioned regular expressions) is wrong.

Pseudocode (been switching between too many languages, of late):

if s.length < 8:
    return False
nUpper = nLower = nAlphanum = nSpecial = 0
for c in s:
    if isUpper(c):
        nUpper++
    if isLower(c):
        nLower++
    if isAlphanumeric(c):
        nAlphanum++
    if isSpecial(c):
        nSpecial++
return (0 < nUpper) and (0 < nAlphanum) and (0 < nSpecial)

Bet you read and understood the above code almost instantly. Bet you took much longer with the regex, and are less certain it is correct. Extending the regex is risky. Extended the immediate above, much less so.

Note also the question is imprecisely phrased. Is the character set ASCII or Unicode, or ?? My guess from reading the question is that at least one lowercase character is assumed. So I think the assumed last rule should be:

return (0 < nUpper) and (0 < nLower) and (0 < nAlphanum) and (0 < nSpecial)

(Changing hats to security-focused, this is a really annoying/not useful rule.)

Learning to know when the question is wrong is massively more important than clever answers. A clever answer to the wrong question is almost always wrong.


As an example how this could be done with a readable/maintainable regex.

For a longer regex you should always use RegexOptions.IgnorePatternWhitespace to allow whitespace and comments in the expression for better readability.

String[] passwords = { "foobar", "Foobar", "Foobar1", "Fooobar12" };

foreach (String s in passwords) {

    Match password = Regex.Match(s, @"
                                      ^              # Match the start of the string
                                       (?=.*\p{Lu})  # Positive lookahead assertion, is true when there is an uppercase letter
                                       (?=.*\P{L})   # Positive lookahead assertion, is true when there is a non-letter
                                       \S{8,}        # At least 8 non whitespace characters
                                      $              # Match the end of the string
                                     ", RegexOptions.IgnorePatternWhitespace);

    if (password.Success) {
        Console.WriteLine(s + ": valid");
    }
    else {
        Console.WriteLine(s + ": invalid");
    }
}

Console.ReadLine();
2012/09/17

If you need only one upper case and special character then this should work:

@"^(?=.{8,}$)(?=[^A-Z]*[A-Z][^A-Z]*$)\w*\W\w*$"
2012/02/28

The regular expression you was looking for is: /^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[[email protected]#\$%\^&\*\[\]"\';:_\-<>\., =\+\/\\]).{8,}$/u.

Example and test: http://regexr.com/3fhr4

2017/03/17

Source: https://stackoverflow.com/questions/9477906
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