Regular Expression: Prevent from matching empty string

Question

I have this regex string

(hour)?|(minute)?|(second)?

which will match hourminutesecond or hourminute or hoursecond...

However, the regex also match an empty string ""

How can I exclude the empty string from the list of matches?

You can try: (?=.)(hour|minute|second)?

anubhava
– anubhava

2020-10-29 06:58:42 +00:00
Commented Oct 29, 2020 at 6:58 — anubhava
– anubhava, Commented Oct 29, 2020 at 6:58

Tim Biegeleisen · Accepted Answer · 2020-10-29 06:59:13Z

1

One quick fix here would be to add a positive lookahead which asserts that at least one character be present:

(?=.)(?:hour)?(?:minute)?(?:second)?

Note that the | in your current pattern are not doing what you think they are. The ? you place after each time term already make each term optional.

Demo

answered Oct 29, 2020 at 6:59

Tim Biegeleisen

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The fourth bird · Accepted Answer · 2020-10-29 16:14:49Z

0

If you don't need the separated capture groups for further processing, you could match at least one of the alternatives making none of them optional using a non capture group (?:

(?:hour|minute|second)

Regex demo

answered Oct 29, 2020 at 16:14

The fourth bird

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