Test if a regular expression is a valid one in PHP

I am writing a form validation class and wish to include regular expressions in the validation. Therefore, the regex provided isn’t guaranteed to be valid.

How can I (efficiently) check that the regex is valid?

Answer

Use the pattern in your preg_* calls. If the function returns false there is likely a problem with your pattern. As far as I know this is the easiest way to check if a regex pattern is valid in PHP.

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Here’s an example specifying the right kind of boolean check:

$invalidPattern = 'i am not valid regex';
$subject = 'This is some text I am searching in';
if (@preg_match($invalidPattern, $subject) === false) {
    // the regex failed and is likely invalid
}