CODEWITHSUNDEEP
javascriptregex
dagda1
dagda1

Reputation: 28760

regex for matching numbers and dashes when in valid

I have the following regex [0-9-]{4}-[0-9-]{2}-[0-9-]{2}$.

I want it not to match when it is an iso date:

e.g. 1970-01-01

But I would like it to match when it is like 1979------ or --------29.

or -----11---.

If I was using just javascript I would say str.indexOf('--') !== -1

Upvotes: 0

Views: 46

Answers (2)

Federico Piazza
Federico Piazza

Reputation: 30985

You can use a trick with a negative lookahead like this:

(?!\d{4}-\d{2}-\d{2})^[0-9-]{4}-[0-9-]{2}-[0-9-]{2}$

Working demo enter image description here

Btw, you can shorten your regex like this:

(?!\d{4}-\d{2}-\d{2})^[\d-]{4}-[\d-]{2}-[\d-]{2}$

Update: as ctwheels mentioned in his comment, you can make the regex more efficient by using anchors in the lookarounds like this:

^(?!\d{4}-\d{2}-\d{2})[0-9-]{4}-[0-9-]{2}-[0-9-]{2}$

Upvotes: 0

Tim Biegeleisen
Tim Biegeleisen

Reputation: 520878

You might find the following pattern satisfactory:

^(?=.*\-\-)(?=.*[0-9]{2})(?:[0-9]{4}|\-{4})-(?:[0-9]{2}|\-{2})-(?:[0-9]{2}|\-{2})$

The first lookahead at the start of the pattern asserts that -- appears at least once, ensuring that the date is not a complete ISO date. The second lookahead asserts that at least one date component is present, preventing ---------- from being a match.

Demo

Upvotes: 1

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