Question

I would like to know how to strip all non-alphanumeric characters from a string except for underscores and dashes in PHP.

Answer 1

Use preg_replace:

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

The first argument to preg_replace is a regular expression. This one contains:

• / – starting delimiter — start the regex
• [ – start character class — define characters that can be matched
• ^ – negative — make the character class match only characters that don’t match the selection that follows
• \w – word character — so don’t match word characters. These are A-Za-z0-9 and _ (underscore)
• - – hyphen — don’t match hypens either
• ] – close the character class
• / – ending delimiter — close the regex

Note that this only matches hyphens (i.e. -). It does not match genuine dash characters (– or —).