$query_string

Description

The `$query_string` variable in NGINX captures the query string from the client's request URI. The query string is part of the URL that follows the '?' character and typically includes parameters and their values. For example, in the URL `http://example.com/index.html?name=John&age=30`, the query string is `name=John&age=30`. This variable is automatically populated by NGINX when a request is received and can be utilized in various contexts, particularly within location blocks where conditional logic is applied. This variable is useful for implementing logic based on the specific parameters passed in a query string. For instance, you can use `$query_string` in rewrites, access control, or logging configuration to direct requests based on their parameters. It is important to note that this variable is a simple string representation of the query string and does not parse its content; it is up to the administrator to handle parsing if more fine-grained control is needed over the parameters themselves.

Config Example

location /search {
    if ($query_string ~* "keyword=(.*)") {
        set $search_keyword $1;
        add_header Search-Keyword "$search_keyword";
    }
}