Question

I need a regular expression to validate a string with the following conditions

1. String might contain any of digits space + – () / .
   If string contain anything else then it should be invalid
2. If there is any + in the string then it should be at the beginning and there should at most one + , otherwise it would be invalid, if there are more than one + then it is invalid
3. String should be 7 to 20 character long
4. It is not compulsory to have all these digits space + – () / .
   But it is compulsory to contain at least 7 digit

Answer 1

I think you are validating phone numbers with E.164 format. Phone number can contain many other format. It can contain . too. Multiple spaces in a number is not uncommon. So its better to format all the numbers to a common format and store that format in db. If that common format is wrong you can throw error.

I validate those phone numbers like this.

function validate_phone($phone){
    // replace anything non-digit and add + at beginning
    $e164 = "+". preg_replace('/\D+/', '', $phone);
    // check validity by length;
    return (strlen($e164)>6 && strlen($e164)<21);
}

Here I store $e164 in Db if its valid.

Even after that you can not validate a phone number. A valid phone number format does not mean its a valid number. For this an sms or call is generated against the number and activation code is sent. Once the user inputs the code phone number is fully validated.