How to write a regex either mathes to empty character set or contains a specific sequence

Question

I need to write a regex for a text-box field validation on the JSF page. I need this field to be an empty, or contains a sequence of [a-z]1[a-z]54. How can I do that?

You don't need to do a regex conditional. Just disjunct the entire regex match with `string.length == 0` — quantumtremor, Dec 26 '14 at 09:09
@MitchWheat I mean, if the string doesn't match [a-z]1[a-z]54 then it shall match an empty string. — St.Antario, Dec 26 '14 at 09:09
@quantumtremor I know, but unfortunately I need to do it via regex. Is it possible — St.Antario, Dec 26 '14 at 09:10
possible duplicate of [Regex empty string or email](http://stackoverflow.com/questions/5063977/regex-empty-string-or-email) — Max Leske, Dec 26 '14 at 10:06
why the vote to close? it's not asking for an off-site resource, there are 3 answers here all basically equivalent — Jasen, Dec 26 '14 at 10:41

score 4 · Answer 1 · answered Dec 26 '14 at 09:14

4

You could try this also,

^([a-z]1[a-z]54)?$

? after the capturing group would make the whole capturing group as an optional one.

DEMO

answered Dec 26 '14 at 09:14

Avinash Raj

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score 3 · Answer 2 · edited Dec 26 '14 at 09:19

3

try this one: ^([a-z]1[a-z]54|)$

edited Dec 26 '14 at 09:19

vks

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answered Dec 26 '14 at 09:11

Jasen

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score 2 · Answer 3 · answered Dec 26 '14 at 09:14

2

This regex may help you ^[a-z]{1,54}$|^$

answered Dec 26 '14 at 09:14

Guillaume S

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How to write a regex either mathes to empty character set or contains a specific sequence

3 Answers3