how to strip all characters except for alphanumeric and underscore and dash?

Question

I'm not an expert with regex:( I'm trying to to strip all characters from the string except for alpanumeric and underscore and dash. Is this the correct syntax?:

preg_replace("/[^a-z0-9_-]+/i", "", $string);

Answer 1

Yes, but it can be optimised slightly:

preg_replace('/[^\w-]/', '', $string);

\w matches alphanumeric characters and underscores. This has the added advantage of allowing accented characters if your locale allows.

Answer 2

What you have looks like it will work. You may want to add spaces since they're not an alphanumeric character:

preg_replace("/[^a-z0-9_-\s]+/i", "", $string);