How to use variables after nginx include statement

Question

like

include $document_root/aaa.txt;

An error will be reported
open() "/etc/nginx/$document_root/aaa.txt" failed (2: No such file or directory) in /etc/nginx/nginx.conf:xxx

The variables after include are not parsed

Answer 1

There were no variables when including it. Variables only appeared very later.

Answer 2

http://nginx.org/en/docs/ngx_core_module.html#include

Syntax: include file | mask;
Default: —
Context: any
Includes another file, or files matching the specified mask, into configuration. Included files should consist of syntactically correct directives and blocks.

Usage example:

include mime.types;
include vhosts/*.conf;