What does the '^' mean in “rewrite ^ http://test.com permanent;”

Question

I found some configuration of nginx contains:

if($args ^~ post=140) {
    rewrite ^ http://test.com/ permanent;
}

What does the ^ mean in rewrite ^ http://test.com/ permanent?

Answer 1

It's a regexp metacharacter that matches the beginning of a string. Since all strings have a beginning, this regexp matches any string.

This is a typical nginx idiom for "redirect any URL to http://test.com/".

The $ metacharacter matching the end of a string would work as well, but ^ seems to be what everybody uses.