How can I validate regex?

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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Alternative - Regular Expression Online Tester

• RegExr
• PHP Regular Expression Tester
• Regular Expression Tool

// 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...

If you want to dynamically test a regex preg_match(...) === false seems to be your only option. PHP doesn't have a mechanism for compiling regular expressions before they are used.

Also you may find preg_last_error an useful function.

On the other hand if you have a regex and just want to know if it's valid before using it there are a bunch of tools available out there. I found rubular.com to be pleasant to use.