Test if a string is regex
php, preg-match, regex
Solution
The only easy way to test if a regex is valid in PHP is to use it and check if a warning is thrown.
ini_set('track_errors', 'on');
$php_errormsg = '';
@preg_match('/[blah/', '');
if($php_errormsg) echo 'regex is invalid';
However, using arbitrary user input as a regex is a bad idea. There were security holes (buffer overflow => remote code execution) in the PCRE engine before and it might be possible to create specially crafted long regexes which require lots of cpu/memory to compile/execute.
Problem
Is there a good way of test if a string is a regex or normal string in PHP? Ideally I want to write a function to run a string through, that returns true or false. I had a look at `preg_last_error()`: ``` <?php preg_match('/[a-z]/', 'test'); var_dump(preg_last_error()); preg_match('invalid regex', 'test'); var_dump(preg_last_error()); ?> ``` Where obviously first one is not an error, and second one is. But `preg_last_error()` returns `int 0` both times. Any ideas?