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

I'm not an expert with regex:( I'm trying to to 开发者_JS百科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);

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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.

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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);

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Yes. :)

http://codepad.org/lkJTRP0P