How can I validate regex?

Question

I'd like to test the validity of a regular expression in PHP, preferably before it's used. Is the only way to do this actually trying a preg_match() and seeing if it returns FALSE?

Is there a simpler/proper way to test for a valid regular expression?

Answer 1

// This is valid, both opening ( and closing ) var_dump(preg_match('~Valid(Regular)Expression~', '') === false); // This is invalid, no opening ( for the closing ) var_dump(preg_match('~InvalidRegular)Expression~', '') === false); 

As the user pozs said, also consider putting @ in front of preg_match() (@preg_match()) in a testing environment to prevent warnings or notices.

To validate a RegExp just run it against null (no need to know the data you want to test against upfront). If it returns explicit false (=== false), it's broken. Otherwise it's valid though it need not match anything.

So there's no need to write your own RegExp validator. It's wasted time...

Answer 2

I created a simple function that can be called to checking preg

function is_preg_error() {     $errors = array(         PREG_NO_ERROR               => 'Code 0 : No errors',         PREG_INTERNAL_ERROR         => 'Code 1 : There was an internal PCRE error',         PREG_BACKTRACK_LIMIT_ERROR  => 'Code 2 : Backtrack limit was exhausted',         PREG_RECURSION_LIMIT_ERROR  => 'Code 3 : Recursion limit was exhausted',         PREG_BAD_UTF8_ERROR         => 'Code 4 : The offset didn\'t correspond to the begin of a valid UTF-8 code point',         PREG_BAD_UTF8_OFFSET_ERROR  => 'Code 5 : Malformed UTF-8 data',     );      return $errors[preg_last_error()]; } 

You can call this function using the follow code :

preg_match('/(?:\D+|<\d+>)*[!?]/', 'foobar foobar foobar'); echo is_preg_error(); 

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