Test if a string is regex

Question

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.

Answer 1

Why not just use...another regex? Three lines, no @ kludges or anything:

// Test this string
$str = "/^[A-Za-z ]+$/";

// Compare it to a regex pattern that simulates any regex
$regex = "/^\/[\s\S]+\/$/";

// Will it blend?
echo (preg_match($regex, $str) ? "TRUE" : "FALSE");

Or, in function form, even more pretty:

public static function isRegex($str0) {
    $regex = "/^\/[\s\S]+\/$/";
    return preg_match($regex, $str0);
}

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This doesn't test validity; but it looks like the question is Is there a good way of test if a string is a regex or normal string in PHP? and it does do that.