Use of if judgment in Nginx configuration

When the rewrite rule of rewrite cannot meet the needs, for example, it is necessary to determine whether the file does not exist or when the path contains xx, etc., then if

if syntax

if (expression) {
    ...
}

Expression syntax:

When an expression is just a variable, if the value is empty or any string starting with 0 will be treated as false
When directly comparing variables and content, use = or !=
-f and !-f are used to determine whether a file exists
-d and !-d are used to determine whether a directory exists
-e and!-e are used to determine whether a file or directory exists
-x and !-x are used to determine whether the file can be executable

In order to configure the conditional judgment of if, the built-in global variable in nginx is required here

$args This variable is equal to the parameter in the request line, the same as $query_string
$content_length Content-length field in the request header.
$content_type Content-Type field in the request header.
$document_root The value specified in the root directive at the current request.
$host Request the host header field, otherwise it is the server name.
$http_user_agent Client agent information
$http_cookie Client cookie information
$limit_rate This variable can limit the connection rate.
$request_method The action requested by the client is usually GET or POST.
$remote_addr The IP address of the client.
$remote_port The client's port.
$remote_user Username that has been verified by Auth Basic Module.
$request_filename The file path of the currently requested, generated by the root or alias directive and the URI request.
$scheme HTTP method (such as http, https).
$server_protocol The protocol used by the request is usually HTTP/1.0 or HTTP/1.1.
$server_addr Server address, this value can be determined after completing a system call.
$server_name Server name.
$server_port The port number that requests to reach the server.
$request_uri The original URI containing the request parameters, not the host name, such as: "/foo/?arg=baz".
$uri Current URI without request parameters, $uri does not contain the host name, such as "/foo/".
$document_uri Same as $uri.

Give an example

1. If the file does not exist, return 400.

if (!-f $request_filename) {
    return 400;
}

2. If host is not, then 301 is in

if ( $host != '' ){
    rewrite ^/(.*)$ /$1 permanent;
}

3. If the request type is not POST, return 405

if ($request_method = POST) {
    return 405;
}

4. If there is any in the parametersa=1Then 301 to the specified domain name

if ($args ~ a=1) {
    rewrite ^ / permanent;
}

5. In a certain scenario, it can be used in combination with location rules, such as:

# When accessing /location = / {
    # Set the default value to xiaowu    set $name xiaowu;
    # If name=xx is included in the parameter, use this value    if ($args ~* name=(\w+?)(&amp;|$)) {
        set $name $1;
    }
    # 301
    rewrite ^ /$ permanent;
}

The above indicates:
/ => /
/?name=ok => /?name=ok

This is the end of this article about the use of if judgment in Nginx configuration. For more related content on Nginx if judgment, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!