Regular Expression For Alphanumeric Characters and Underscores and character Limit

Question

I would like to have a regular expression that checks if a string contains upper and lowercase letters, numbers, and underscores as well as a character limit. These are the only Types allowed in the string.

However, the string does not have to contain all of the specified arguments.

Meaning that the string could be alphanumeric or alphanumeric with underscores or just numbers or just letters ETC.

I followed the suggestions provided here: Regular Expression for alphanumeric and underscores

and came up with the following Expression: ^([a-zA-Z0-9_]){3,15}$

So the Question is: What Is wrong with my REGEX?

And what is your question? Do you want us to test your regex for you? — Wiktor Stribiżew, May 02 '17 at 14:24
The following Regex only checks if the string Matches Fully meaning the string must contain all specified arguments. @WiktorStribiżew — KING, May 02 '17 at 14:26
So, what is the question? Matching 3 to 15 alphanum/`_` chars in a string with any other chars? — Wiktor Stribiżew, May 02 '17 at 14:26
The question is what is wrong with my REGEX @WiktorStribiżew — KING, May 02 '17 at 14:27
Well, if I guessed the requirements right in my above comment, you need `Regex.IsMatch(s, "(?:[^a-zA-Z0-9_]*[a-zA-Z0-9_]){3}")` — Wiktor Stribiżew, May 02 '17 at 14:28
@WiktorStribiżew I believe that Works made a slight change but if you post your answer I'll mark it as the correct one — KING, May 02 '17 at 14:38

Wiktor Stribiżew · Accepted Answer · 2017-05-02T14:49:48.247

Your regex - ^([a-zA-Z0-9_]){3,15}$ - matches a whole string that is 3 to 15 chars long and only consists of ASCII letters, digits or _ symbol.

It appears you want to detect a string that contains at least 3 characters from the specified ranges (letter/digit/underscore).

You may use

[a-zA-Z0-9_](?:[^a-zA-Z0-9_]*[a-zA-Z0-9_]){2}

Or a less linear:

(?:[^a-zA-Z0-9_]*[a-zA-Z0-9_]){3}

Use the patterns with Regex.IsMatch, this method allows partial matches.

Details:

[a-zA-Z0-9_] - matches a single char from the ranges specified
(?: - start of a non-capturing group matching a sequence of....
- [^a-zA-Z0-9_]* - 0+ chars other than those defined in the negated character class
- [a-zA-Z0-9_] - a char from the ranges specified
){2} - ....2 times exactly.

Regular Expression For Alphanumeric Characters and Underscores and character Limit

1 Answers1