Nginx HTTP Server - Fourth Edition

Captures

One last feature of the regular expression mechanism is the ability to capture sub-expressions. Whatever text is placed between parentheses ( ) is captured and can be used after the matching process. The captured characters become available under the form of variables called $N, where N is a numeric index, in order of capture. Alternatively, you can attribute an arbitrary name to each of your captures (see the following example). The variables generated through the captures can be inserted within directive values.

Here are a couple of examples to illustrate the principle:

Pattern	Example of a matching string	Captured
^(hello|hi) (sir|mister)$	hello sir	$1 = hello $2 = sir
^(hello (sir))$	hello sir	$1 = hello ...