Nginx rewrite syntax

Question

I've seen a bunch of ngnix rewrites that have syntax like this:

server {
    server_name  www.example.com;
    rewrite ^(.*) http://example.com$1 permanent;
}

I don't understand the ^(.*) part. Does the ^ take everything after the TLD of the uri?

Answer 1

The ^ does indeed match at the beginning of the string. In the case of nginx's rewrite directive this means the beginning of the path component of the actual URI. Unfortunately nginx's documentation is slightly incorrect. Quoting from http://www.nginx.org/en/docs/http/ngx_http_rewrite_module.html#rewrite :

If the specified regular expression matches a URI, the URI is changed as specified in the replacement string.

However, this is technically wrong. rewrite does not match the whole URI/URL but only its path component (which always starts with a / even if the user only enters e.g. http://www.example.com instead of http://www.example.com/). Therefore rewrite ^(.*) http://example.com$1 permanent; does not turn into http://example.comwww.example.com.

Answer 2

If I remember it correctly, the ^ just sets the Regex rule to match the start of the string. The parentheses are used to extract that part with the $1-9 variables.

Another solution from the Nginx wiki. Link

server {
   server_name www.example.com;
   rewrite ^ http://example.com$request_uri? permanent;
}