Tricky regex validation

Question

I need to validate string with 2 groups which are separated with one space with next rules:

Each group needs to be at least 2 character long but less or equal to 15
Both groups together can't be more than 20 chars long (not counting space)
Groups can only contain letters (that's simple, it's [a-zA-Z])

Following these rules, here are some examples

Firstname Lastname (Valid)
Somename T (Invalid, 2nd one is <2)
Somethingsomettt Here (Invalid, first one is > 15)
Somethingsome Somethingsome (Invalid, total > 20)

It'd be simple [a-zA-Z]{2,15} [a-zA-Z]{2,15} if it wasn't for that 2+2<=total<=20 condition.

Is it even possible to limit it this way? If it is - how?

UPDATE Just for the sake of it, resulting regex was supposed to be ^(?=[a-zA-Z ]{5,21}$)[a-zA-z]{2,15} [a-zA-Z]{2,15}$, @vks was closest one to it. Nevertheless, thanks @popovitsj and @Avinash Raj too.

Why not split on the space in the middle, and separately validate both pieces? This would allow you to trivially check the combined length. — ajp15243
– ajp15243, Commented Sep 29, 2014 at 18:43
Is there a reason you have to do this with one regular expression? — Bryan Oakley
– Bryan Oakley, Commented Sep 29, 2014 at 18:44
Looks like you have an extra - in the middle of your first character class ([a-z-A-Z]). — ajp15243
– ajp15243, Commented Sep 29, 2014 at 18:47

vks · Accepted Answer · 2014-09-29 19:09:24Z

1

^(?=.{5,21}$)[a-zA-Z]{2,15} [a-zA-Z]{2,15}$

Try this.See demo.

http://regex101.com/r/nA6hN9/30

edited Sep 29, 2014 at 19:09

answered Sep 29, 2014 at 18:56

vks

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wvdz · Accepted Answer · 2014-09-29 19:00:45Z

1

This can be done with lookahead. Something like this:

^(?=.{1,20}$)[a-zA-z]{2,14} [a-zA-Z]{2,14}$

edited Sep 29, 2014 at 19:00

answered Sep 29, 2014 at 18:46

wvdz

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13 Comments

Igor Yavych Over a year ago

Thanks, modified it to ^(?=[a-zA-Z ]{4,21}$)[a-zA-z]{2,15} [a-zA-Z]{2,15}$ which seems to work like I need.

Avinash Raj Over a year ago

@Flyer did you want to match Somethings Somethings?

vks Over a year ago

@Flyer this is incorrect.the minimum should be 5 not 4.

Igor Yavych Over a year ago

@Avinash Raj, yeah it should match since both are >=2 <=15, and total is 20 (not counting space)

wvdz Over a year ago

Who cares 14 or 15... and yours is incorrect too, it matches also tabs and enters instead of just a space in the middle.

|

Avinash Raj · Accepted Answer · 2014-09-29 19:13:32Z

1

You could try the below regex which uses negative lookahead,

(?!^.{22,})^[a-zA-Z]{2,15} [a-zA-Z]{2,15}$

DEMO

edited Sep 29, 2014 at 19:13

answered Sep 29, 2014 at 18:46

Avinash Raj

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