RegEx to not to contain "--"

Question

I want to validate a string with alpha numeric values, but if the string contains -- (double dash) anywhere in the string, it should be invalid.

valid:

• apple123
• -apple-123
• app-le123
• a-p-p-l-e-1-2-3

invalid:

• --apple123
• app--le123

---

https://stackoverflow.com/a/1240365/1920590

The above old post have the answer ^(?!.*bar).*$ which does the negation, but it does not work for same character repetition like --.

Can anyone help me to figure out to modify the ^(?!.*bar).*$ to identify -- as a string.

Answer 1

You may use a negative lookahead:

^(?!.*--)[\w-]+$

• (?!.*--) is a negative lookahead assertion that will fail the match if -- appears anywhere in input.
• [\w-] matches a word character [a-zA-Z0-9_] or a hyphen

RegEx Demo