What is "~" in regex? [duplicate]

Question

Possible Duplicate:
Tilde operator in Regular expressions

echo preg_replace_callback('~-([a-z])~', function ($match) {
    return strtoupper($match[1]);
}, 'hello-world');

The code is from http://php.net/manual/en/functions.anonymous.php

I searched for what "~" is in regex and did not find an answer.

What does it do?

Answer 1

The first and last character of a regular expression in PHP (and other implementations) is known as the delimiter. Normally, you see a / being used, but in this case, someone chose ~. Read more here.

Not sure why ~ was chosen though; probably a habit of that particular developer. Normally, one chooses a different delimiter over / when the regular expression itself will contain slashes (e.g. matching URLs), so that slashes don't need to be escaped every time.

Answer 2

The symbol ~ is just used as delimiter in PHP regexps.