Regular Expression to Validate Specific Input While Allowing Empty Input

Question

I'm trying to validate a textbox containing a variety of acceptable inputs:

"123456789"
"123456789+1"
""

I'm using this regular expression to validate the first two conditions:

^[0-9]{9}\+[0-9]$

But now I can't figure out how to allow the user not to enter anything, I've tried things like encapsulating the expression in ()? , or changing the {9} to {0,9}, but this allows for a variable number of numbers in the first group (as it MUST be 9, or none)

Any help would be greatly appreciated!!

Brian Campbell · Accepted Answer · 2010-09-02 20:27:26Z

3

Try

^([0-9]{9}\+[0-9])?$

The ? means "0 or 1 copies of the preceding expression." In this case, the entire parenthesized expression is made optional.

Also, if you want the \+[0-9] part to be optional, you will likely want to do the same to that; wrap in in parentheses and make it optional with ?:

^([0-9]{9}(\+[0-9])?)?$

edited Sep 2, 2010 at 20:27

answered Sep 2, 2010 at 20:14

Brian Campbell

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3 Comments

Brett Over a year ago

This one allows me to have options 2 and 3 from my list, but not option 1

Brian Campbell Over a year ago

@Brett My second example should allow you to have option 1 as well. You can test it here: rubular.com/r/bxFzEVFMZO

Brett Over a year ago

Wonderful, thanks!! yeah, that makes sense to have the second part in parenthesis too, I've been reading about these and feel like I'm learning a bit, but keep getting hic-cups.. thanks!

Charles · Accepted Answer · 2010-09-02 20:15:34Z

1

^(?:[0-9]{9}\+[0-9])?$

answered Sep 2, 2010 at 20:15

Charles

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1 Comment

Brett Over a year ago

Like Brian, this one allows me to have options 2 and 3 from my list, but not option 1

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