Trying to create a regex for HH:MM A

Question

Trying to create a regular expression HH:MM A. required two digit for HH and MM and space then Meridien AM/PM - caps only.

Find many answers on other posts but it didn't work exactly. Mostly I used to do with time picker control. But wants to go with regex for current scenario.

((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AP][M]))

above one also allowed, 1:23 AM or 1:23AM. Need only, 01:23 AM allowed. 12 hours format. can you guide on this. It allows leading 0 and space options. Thanks.

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spender · Answer 1 · 2021-06-30T00:42:43.550

2

Yes. The second alternative for the first 2 digits allows the 0 to be optional.

Just remove the "zero or one" quantifier ? from the 0 and you'll make it non-optional:

((1[0-2]|0[1-9]):([0-5][0-9]) ?([AP]M))

You can use exactly the same technique to make the optional (space) character non-optional too.

BTW [MM] is equivalent to just M

edited Jun 30 '21 at 00:42

answered Jun 30 '21 at 00:32

spender

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thanks for comments. this also allows, `02:10AM` as valid, but valid needs to be, `02:10 AM` (with a space). I am not sure which expression needs to be added for one space. – user16346412 Jun 30 '21 at 00:34
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@user16346412 So, I've just explained how to make an optional quantifier go away. There's only one left in the expression. Can you spot it? – spender Jun 30 '21 at 00:37
:) Thanks @Spender, looks like, this is able to work, just removed `?` as spotted above, so expression like, `((1[0-2]|0[1-9]):([0-5][0-9]) ([AP]M))` – user16346412 Jun 30 '21 at 00:39
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Why did you include `?` in the first place if you clearly want the space to be mandatory? – Hao Wu Jun 30 '21 at 00:40
I found this expression from some post and then played around and filtered out close to my need. But was not sure exactly on how it decodes. And missed that. Thanks for all comments. – user16346412 Jun 30 '21 at 00:44

score 0 · Accepted Answer · answered Jun 30 '21 at 00:39

0

You can use regex demo

(?:(?:0[1-9])|(?:1[0-2])):(?:[0-5][0-9]) [AP]M

answered Jun 30 '21 at 00:39

DecPK

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One thing, why its using `?:` for each expression group ? – user16346412 Jun 30 '21 at 00:49
It won't capture the group if you add `?:` [read](https://stackoverflow.com/questions/3705842/what-does-do-in-regex). That means whatever is matched in (?:_______), even though it's enclosed by () it won't appear in the list of matches – DecPK Jun 30 '21 at 00:50
Ok. Got it. It will not capture (). Thank you again, its really detail and useful. – user16346412 Jun 30 '21 at 00:56
You don't need the non capture groups. `(?:0[1-9]|1[0-2]):[0-5][0-9] [AP]M` See https://regex101.com/r/SK3ERg/1 – The fourth bird Jun 30 '21 at 08:58
@decpk How did you generate that spanky image? – spender Jun 30 '21 at 09:35

Trying to create a regex for HH:MM A

2 Answers2