Regex to allow only particular numbers

Question

I have a field which should only take values divisible of 12. Such as 12,24,36,48,60,72,84,96,108,120. I used below regex :

12|24|36|48|60|72|84|96|108|120

But this also allows values such as 12abc, 12-!&. It's allowing alphabets or special characters with the numbers. Is there any regex to only allow 12,24,36,48,60,72,84,96,108,120 as input.

if you only need those specific numbers you could put a start and end char to the regex ^(12|24|36|48|60|72|84|96|108|120)$, but in general I think @Pointy is right. — Carlo Moretti
– Carlo Moretti, Commented Aug 9, 2019 at 15:07
function isValid (input){ return (input % 12 === 0) && (input>11) && (input<121); } function doingStuffWithInput(input) { if (isValid(input)){ //do stuff } else{ alert("error, not valid"); } If you wish to do it without regex — Sharon
– Sharon, Commented Aug 9, 2019 at 15:13
This page about anchors might be helpful rexegg.com/regex-anchors.html — The fourth bird
– The fourth bird, Commented Aug 9, 2019 at 15:16

Sean T · Accepted Answer · 2019-08-09 15:09:01Z

3

If you're using html5 controls use step, min and max.

<input type="number" step="12" min="0" max="120" name="multiplesOfTwelve"/>

edited Aug 9, 2019 at 15:09

answered Aug 9, 2019 at 15:08

Sean T

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7 Comments

Pointy Over a year ago

Probably also min=0 or min=12

collapsar Over a year ago

You'd still need server-side validation ( and that should not be regex-based ) to filter for fabricated POST requests.

Sean T Over a year ago

@collapsar They've not specified what server side framework they're using so it's hard for me to state that :)

T.J. Crowder Over a year ago

@collapsar - Well, that's a truism, not really a specific to Sean's answer. :-) No client-side validation is sufficient on its own.

collapsar Over a year ago

@T.J.Crowder You are right. The Q however only asks for (regex-based) validation in general which would include client- and server-side, while this answer is limited to the client.

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T.J. Crowder · Accepted Answer · 2019-08-09 15:13:03Z

I agree with Pointy that this doesn't sound like a job for regex. If you're using HTML5 input validation, definitely go for the approach Sean T shows.

But from what you've said it's matching, it's just that you don't have start-of-input (^) and end-of-input anchors ($):

^(?:12|24|36|48|60|72|84|96|108|120)$

(You need the non-capturing group or the anchors become part of the alternative they're next to.)

If you want to allow harmless spaces:

^\s*(?:12|24|36|48|60|72|84|96|108|120)\s*$

Obviously in either case (doing something like this or Sean's HTML5 approach), if this is being sent to a server, you need to validate it on the server as well.

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