In PHP, how do I allow "." and "-" using preg_match?

Question

I am trying to write a preg_match expression that will allow "." or "-" along with any letters or numbers, but I can't figure out how to do it.

Here is what I have:

preg_match("/^_?\w $/", $userName)

Any suggestions?

Thanks!

Answer 1

dot and dash are special pattern modifiers but you can escape them using backslashes to use them in patterns.

Here is the regexp you are asking for:

preg_match('{^_?[a-z0-9_\\.\\- ]+$}i', $userName);

Some explanation:

* I used single quotes just cuz i prefer them (:

* I used curly brackets to enclose the regexp... many characters can be used for this purpose including /

* I used double back-slashes. Two \\ evaluates to one \ inside single quoted string and then when this goes to preg engine, it escapes the next character (dot and dash)

* plus indicates one or more of the characters from the preceding group