How to express the following regex expression?

Question

I am poor with Regular expressions, following is the requirement. I will be using this with Joi validators.

ID :

Name:

Should be alphanumeric
Cannot have any special characters except dash and underscore (- and _), but space is allowed.
Cannot have - or _ consecutively (Example: this-id is ok but this--id is not.

Have you looked at this: [Regular expression to validate username](https://stackoverflow.com/questions/12018245/regular-expression-to-validate-username) — quackenator, May 31 '17 at 18:34
You can experiment with regular expressions on websites like https://regex101.com/. Its a good way to learn how to match specific text. — DeathByTensors, May 31 '17 at 18:36

degant · Accepted Answer · 2017-05-31T19:26:48.457

3

Regex for ID:

^[-_]?(?:[A-Za-z0-9]+[-_]?)+$

[-_]? allows underscore or hyphen to appear at the start too
[A-Za-z0-9]+ matches one or more alphanumeric characters
[-_]? allows zero or one hyphen or underscore
Whole pattern is surrounded within a non capturing group and a + to indicate that it may repeat one or more times

Thus is ensures that no 2 hyphens or underscores appear in succession

Regex for Name:

^[-_]?(?:[A-Za-z0-9 ]+[-_]?)+$

EDIT: Improvement to fix underscore or hyphen appearing at the start too. Thanks to @ErikBrodyDreyer for the catch! :)

edited May 31 '17 at 19:26

answered May 31 '17 at 18:50

degant

That won't match the case where the ID begins with a hyphen or underscore, if that case needs to be accepted too. – E.D. May 31 '17 at 19:17
2

@ErikBrodyDreyer good point, missed that. Can be fixed by adding `[-_]?` at the start, outside the non-capturing group – degant May 31 '17 at 19:22

score 0 · Answer 2 · answered May 31 '17 at 19:23

0

([a-zA-Z0-9]*(_)?(?!\2)(\-)?(?!\3))+

this will do the work it will match also -_ prefix

answered May 31 '17 at 19:23

Or Davidi

score 0 · Answer 3 · answered May 31 '17 at 19:24

0

ID : ^(?!.*([_-])\1)[\w-]+$

Name : ^(?!.*([_-])\1)[\w -]+$

A \w is the same as [A-Za-z0-9_], so the underscore is included.

The (?!.*([_-])\1) is a negative lookahead that won't allow a double dash or double underscore after the start of the string ^.

answered May 31 '17 at 19:24

LukStorms

3 Answers3