Question

I am using regular expression to validate the mobile number with the following criteria:

1. Maximum of 12 numbers.
2. It should start with Zero.
3. Will allow only one space (at a non-defined point)
4. Followed by an optional extension number of up to five digits in length, not including the # sign

My Regular Expression looks like below: (I have tested this with “rubular” tester)

^((0((?=\d* \d*#)[\d ]{,11})(#\d{,5})?)|(0(?:\d{,10})(#\d{,5})?)|(0((?=\d* \d*$)[\d ]{,11})))$

But it’s not working in .net regular expression engine.

Can someone tell me, in the above one which part doesn’t work with .net regular expression engine? and if I can change anything in the above expression will it work in .Net regular expression engine?

Answer 1

The only problem in your regex is that you are not specifying the starting range anywhere.. so it should be {0,11} or {1,11} not {,11}

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You can also use this simplified regex

^(?=(\S*[\s]\S*|\S*)$)0(\s?\d){1,11}\s?(#(\s?\d){1,5})?\s?$

\S matches any character that is not space

(\S*[\s]\S*|\S*)$ matches 0 to many non space character followed by a space followed by 0 to many non space characters till end OR it matches all the non space character till end

(?=) is a positive lookahead which check if particular pattern occurs and if not it will not match!