c# - How Do I format a telephone number using regex -

i need format telephone numbers in specific way. unfortunately business rules prohibit me doing front. (separate input boxes etc..)

the format needs +1-xxx-xxx-xxxx "+1" constant. (we don't business internationally)

here regex pattern test input:

"\\d*([2-9]\\d{2})(\\d*)([2-9]\\d{2})(\\d*)(\\d{4})\\d*" 

(which stole somewhere else)

then perform regex.replace() so:

regex.replace(telephonenumber, "+1-$1-$3-$5"); **this blows up** 

if telephone number has "+1" in string, prepends +1-+1-xxx-xxx-xxxx

can please help?

you can add (?:\+1\d*)? catch optional prefix before number. it's caught replaced if it's there.

you don't need use \d* before , after number. optional, don't change anything.

you don't need capture parts won't use, makes easier see ends in replacement.

str = regex.replace(str, @"(?:\+1\d*)?([2-9]\d{2})\d*([2-9]\d{2})\d*(\d{4})", "+1-$1-$2-$3"); 

you might consider using more specific \d* separators though, example [\- /]?. non-specific pattern risk catching that's not phone number, example changing "i have 234 cats, 528 dogs , 4509 horses." "i have +1-234-528-4509 horses.".

str = regex.replace(str, @"(?:\+1[\- /]?)?([2-9]\d{2})[\- /]?([2-9]\d{2})[\- /]?(\d{4})", "+1-$1-$2-$3");