I am writing a PHP script that accepts a regular expression pattern from the user which is used by preg_match(). How can I check that the pattern is valid?
Just test it.
preg_match() will return
FALSE if the pattern is not valid.
Return values: preg_match() returns the number of times pattern matches. That will be either 0 times (no match) or 1 time because preg_match() will stop searching after the first match. preg_match_all() on the contrary will continue until it reaches the end of subject. preg_match() returns FALSE if an error occurred.