RegEx preceded dash

Question

I want to code a regular expression pattern that needs to check the following:

Every dash (-) character must be immediately preceded and followed by a letter or number; consecutive dashes are not permitted.

How to do this?

provide some examples for valid and invalid matches. – Avinash Raj Dec 10 '14 at 04:18 — Avinash Raj, Dec 10 '14 at 04:18

Avinash Raj · Answer 1 · 2014-12-10T06:07:59.953

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You could use the below simple regex which uses negative lookahead assertion.

^(?!-|.*-$|.*-[\W_]|.*[\W_]-).*$

DEMO

.*-[\W_]|.*[\W_]- part in the negative lookahead assertion ensures that the - isn't preceded nor followed by a non-word character or _ symbol.

edited Dec 10 '14 at 06:07

answered Dec 10 '14 at 04:18

Avinash Raj

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score 0 · Accepted Answer · answered Dec 10 '14 at 04:29

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^(?!(?:.*-(?=$|-))|-).*$

Try this.See demo.

https://regex101.com/r/aZ6zX0/4

This uses negative lookahead to make sure - is not followed by - or $ and does not start with -.

answered Dec 10 '14 at 04:29

vks

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This one successfully validates `@-#`, which is obviously not a valid input. – Alex Skalozub Dec 10 '14 at 06:02
@AlexSkalozub that's an easy fix.You can replace `.*` by whatever you want.But OP has not specified anything – vks Dec 10 '14 at 06:03

score 0 · Answer 3 · answered Dec 10 '14 at 05:58

We only know every dash should be surrounded with letters or digits, but we have no clue if the whole string is limited to letters, digits and dashes. Also it was not specified if string is required to contain dashes at all.

Assuming @#$abc-def#% is a valid string, we need to go with something like:

@"^[^-]+?(?:(?<=[\da-z])-(?=[\da-z])[^-]+?)*$"

DEMO

If only letters, digits and dashes are allowed, it is even simpler:

@"^[\da-z]+(?:-[\da-z]+)*$"

DEMO

RegEx preceded dash

3 Answers3