詳細解釋：nginx中ngx_http_rewrite_module模組配置及各個參數含義

This module makes it possible to change URI using regular expressions, and to redirect and select configuration depending on variables.

該模組允許使用Regex改變URI，並且根據變數來轉向以及選擇配置。

If the directives of this module are given at the server level, then they are carried out before the location of the request is determined. If in that selected location there are further rewrite directives, then they also are carried out. If the URI changed
as a result of the execution of directives inside location, then location is again determined for the new URI.

如果在server層級設定該選項，那麼他們將在location之前生效。如果在location還有更進一步的重寫規則，location部分的規則依然會被執行。如果這個URI重寫是因為location部分的規則造成的，那麼location部分會再次被執行作為新的URI。

This cycle can be repeated up to 10 times, after which Nginx returns a 500 error.

這個迴圈會執行10次，然後Nginx會返回一個500錯誤。

Directives[#break break][#if if][#return return][#rewrite rewrite][#set set][#uninitialized_variable_warn uninitialized_variable_warn]

break
文法: break

預設值: none

範圍: server, location, if

Completes the current set of rules. 作用是完成當前的規則列

樣本:

if ($slow) {: limit_rate  10k;: break;}

if
文法: if (condition) { ... }

預設: none

範圍: server, location

Checks the truth of a condition. If the condition evaluates to true, then the code indicated in the curly braces is carried out and the request is processed in accordance with the configuration within the following block. Configuration inside directive if
is inherited from the previous level.

They can be assigned as the condition: 條件陳述式可以使下列的幾種：

the name of variable; false values are: empty string "", or any string starting with "0";
 一個變數的名稱；如果變數的值為空白字串""或者任何以0開始的字串，則表示條件陳述式的值為假
the comparison of variable with the line with using the = and != operators;
pattern matching with regular expressions using the symbols ~* and ~:
Regex形式的模式比對，如~*和~
~ is case-sensitive match;
‘~’表示大小寫敏感的匹配
~* specifies a case-insensitive match (firefox matches FireFox)
‘~*’表示大小寫不敏感的匹配（例如：“firefox”字串可以成功匹配“FireFox”）
!~ and !~* mean the opposite, "doesn't match"
 !~和!~*代表跟後面的正則匹配規則相反的規則，表示不能匹配當前Regex規則的字串執行後面的處理語句
checking for the existence of a file using the -f and !-f operators;使用-f參數以及!-f參數檢測一個檔案是否存在
checking existence of a directory using the -d and !-d operators;使用-d參數以及!-d參數檢測一個目錄（路徑）是否存在
checking existence of a file, directory or symbolic link using the -e and !-e operators;
使用-e以及!-e檢測是否存在一個檔案，一個目錄或者一個符號連結。

checking whether a file is executable using the -x and !-x operators.使用-x以及!-x檢測一個檔案是否可執行

Parts of the regular expressions can be in parentheses, whose value can then later be accessed in the $1 to $9 variables.

Regex部分可以嵌套，運算式後面的部分如果用到前面的運算式可以用 $1 到$9 變數表示。

Examples of use: 例子如下：

if ($http_user_agent ~ MSIE) {: rewrite  ^(.*)$  /msie/$1  break;}if ($http_cookie ~* "id=([^;] +)(?:;|$)" ) {: set  $id  $1;}if ($request_method = POST ) {: return 405;}if (!-f $request_filename) {: break;: proxy_pass  http://127.0.0.1;}if ($slow) {: limit_rate  10k;}if ($invalid_referer) {: return   403;}

The value of the built-in variable $invalid_referer is given by the directive valid_referers.

 

return
文法: return code

預設值: none

範圍: server, location, if

This directive concludes execution of the rules and returns the status code indicated to client. It is possible to use the following values: 204, 400, 402-406, 408, 410, 411, 413, 416 and 500-504. Furthermore, nonstandard code 444 closes the connection without
sending any headers.

這個指令根據規則的執行情況，返回一個狀態值給用戶端。可使用值包括：204，400，402-406，408，410，411，413，416以及500-504。也可以發送非標準的444代碼-未發送任何頭資訊下結束串連。

rewrite
文法: rewrite regex replacement flag

預設: none

範圍: server, location, if

This directive changes URI in accordance with the regular expression and the replacement string. Directives are carried out in order of appearance in the configuration file.

這個指令根據Regex或者待替換的字串來更改URI。指令根據設定檔中的先後順序執行生效。

Be aware that the rewrite regex only matches the relative path instead of the absolute URL. If you want to match the hostname, you should use an if condition, like so:

注意：重寫規則只匹配相對路徑（不包括絕對的URL）。如果你想配對主機名稱，你應該使用if語句，如下：

if ($host ~* www\.(.*)) {: set $host_without_www $1;: rewrite ^(.*)$ http://$host_without_www$1 permanent; # $1 contains '/foo', not 'www.mydomain.com/foo'}

Flags make it possible to end the execution of rewrite directives. flag標記可以停止重新導向規則的執行

If the replacement string begins with http:// then the client will be redirected, and any further rewrite directives are terminated. 如果替換字串以“http:”開始，用戶端會被重新導向，而且其他的重新導向規則都會被終止。

Flags can be any of the following: 可用的flag標記有：

last - completes processing of rewrite directives, after which searches for corresponding URI and location
 完成該rewrite規則的執行，之後尋找符合的URI和location
break - completes processing of rewrite directives
 終止匹配，不再匹配後面的規則
redirect - returns temporary redirect with code 302; it is used if the substituting line begins with http://
 返回302臨時重新導向，當替代行以http:開始時可以使用，地址欄會顯示跳轉後的地址
permanent - returns permanent redirect with code 301
 返回301永久重新導向
Note that if an redirect is relative (has no host part), then when redirecting Nginx uses the "Host" header if the header match name of server_name directive or the first name of server_name directive, if the header does not match or is absent. If no server_name
is set, then the local hostname is used. If you want Nginx to always use the "Host" header, you can use a wildcard "*" server_name (but see the restrictions on doing so).Example:

 

rewrite  ^(/download/.*)/media/(.*)\..*$  $1/mp3/$2.mp3  last;rewrite  ^(/download/.*)/audio/(.*)\..*$  $1/mp3/$2.ra   last;return   403;

But if we place these directives in location /download/, then it is necessary to replace flag "last" by "break", otherwise nginx will hit the 10 cycle limit and return error 500:

如果我們將當前的匹配規則使用在/download/目錄下，就要將"last"替換為"break"了。否則nginx就會達到10次迴圈的上限，然後返回個500錯誤

location /download/ {: rewrite  ^(/download/.*)/media/(.*)\..*$  $1/mp3/$2.mp3  break;: rewrite  ^(/download/.*)/audio/(.*)\..*$  $1/mp3/$2.ra   break;: return   403;}

If in the line of replacement arguments are indicated, then the rest of the request arguments are appended to them. To avoid having them appended, place a question mark as the last character:

: rewrite  ^/users/(.*)$  /show?user=$1?  last;

注: 對花括弧( { 和 } )來說, 他們既能用在重新導向的Regex裡，也是用在設定檔裡分割代碼塊, 為了避免衝突, Regex裡帶花括弧的話，應該用雙引號（或者單引號）包圍。比如，要將類似以下的url

 

/photos/123456 

重新導向到：

 

/path/to/photos/12/1234/123456.png 

可以用以下方法 (注意雙引號):

rewrite  "/photos/([0-9] {2})([0-9] {2})([0-9] {2})" /path/to/photos/$1/$1$2/$1$2$3.png; 

set
syntax: set variable value

default: none

context: server, location, if

Directive establishes value for the variable indicated. As the value it is possible to use a text, variables and their combination.

uninitialized_variable_warn
syntax: uninitialized_variable_warn on|off

default: uninitialized_variable_warn on

context: http, server, location, if

Enables or disables logging of warnings about noninitialized variables.

Internally, the rewrite directives are compiled at the time the configuration file is loaded into internal codes, usable during the request by the interpreter.

This interpreter is a simple stack virtual machine. For example, the directive:

location /download/ {: if ($forbidden) {: return   403;: }: if ($slow) {: limit_rate  10k;: }: rewrite  ^/(download/.*)/media/(.*)\..*$  /$1/mp3/$2.mp3  break;}

will be compiled into this sequence:

: variable $forbidden: checking to zero: recovery 403: completion of entire code: variable $slow: checking to zero: checkings of regular expression: copying "/": copying $1: copying "/mp3/": copying $2: copying "..mpe": completion of regular expression: completion of entire sequence

 

Note that there is no code for directive limit_rate, since it does not refer to module ngx_http_rewrite_module. The "if" block exists in the same part of the configuration as the "location" directive.

If $slow is true, then what's inside the "if" block is evaluated, and in this configuration limit_rate it is equal to 10k.

Directive:

: rewrite  ^/(download/.*)/media/(.*)\..*$  /$1/mp3/$2.mp3  break;

It is possible to reduce the sequence, if in the regular expression we include the first slash inside the parentheses:

: rewrite  ^(/download/.*)/media/(.*)\..*$  $1/mp3/$2.mp3  break;

then the sequence will appear like this:

: checking regular expression: copying $1: copying "/mp3/": copying $2: copying "..mpe": completion of regular expression: completion of entire code

References
Original Documentation：http://sysoev.ru/nginx/docs/http/ngx_http_rewrite_module.html