Question

Problem Statement:

I’m trying to build a regular expression which accepts two consecutive special characters like: /_ or \\ or ./ or -- or \- or any other combination of special charcters (./\_-),in the regular expression mentioned below:

^[a-zA-Z0-9\d]{1}[a-zA-Z0-9\d._/\-]{0,49}$

What i’m doing wrong here?

Answer 1

mlorbetske’s regex can be rewritten a bit to remove the use of conditional regex. I also remove the redundant 0-9 from the regex, since it has been covered by \d.

^[a-zA-Z\d](?:[a-zA-Z\d]|(?<![._/\\\-])[._/\\\-]){0,49}$

The portion (?:[a-zA-Z\d]|(?<![._/\\\-])[._/\\\-]) matches alphanumeric character, OR special character ., _, /, \, - if the character preceding it is not a special character already. I also make the group non-capturing (?:pattern), since it seems that the regex is used for validation only.

I made use of the zero-width negative look-behind assertion (?<!pattern) to assert the character in front is not one of the special characters.