如何在Nginx conf文件中定义全局变量 [英] How to define a global variable in nginx conf file

问题描述

如何在nginx conf文件中定义全局变量，如何在http块中定义全局变量，下面的所有服务器和位置都可以使用它.

How to define a global variable in nginx conf file, define a global var in http block,and all servers and locations below can use it.

http{
      some confs
      ...
      //define a global var mabe like
      set APP_ROOT /home/admin
      // and it can be use in all servers and locations below, like
      server {
        root $APP_ROOT/test1
      }

      server {
        root $APP_ROOT/test2
      }
  }

推荐答案

您可以做一些技巧.如果必须从一个http块中的每个server块访问此值，则可以使用map指令.这将如何运作?
map指令允许您在http块中的任何位置使用变量，该变量的值将在某些映射键上进行计算.讲故事的例子:

You can do a little trick. If this value must be accessible from every server block in one http block you can use map directive. How will this work?
The map directive allows you to use a variable anywhere in an http block which value will be calculated on some map key. All-telling example:

http {

  ...

  /* 
     value for your $my_everywhere_used_variable will be calculated
     each time when you use it and it will be based on the value of $query_string.
  */
  map $query_string $my_everywhere_used_variable {

    /* 
       if the actual value of $query_string exactly match this below then 
       $my_everywhere_used_variable will have a value of 3
    */
    /x=1&y=2&opr=plus     3;

    /* 
       if the actual value of $query_string exactly match this below then
       $my_everywhere_used_variable will have a value of 4
    */
    /x=1&y=4&opr=multi    4;

  /*
    it needs to be said that $my_everywhere_used_variable's value is calculated each
    time you use it. When you use it as pattern in a map directive (here we used the
    $query_string variable) some variable which will occasionally change 
    (for example $args) you can get more flexible values based on specific conditions
  */
  }

  // now in server you can use this variable as you want, for example:

  server {

    location / {
      rewrite .* /location_number/$my_everywhere_used_variable;
      /* 
         the value to set here as $my_everywhere_used_variable will be
         calculated from the map directive based on $query_string value
      */
    }
  }
}

那么，现在这对您意味着什么?您可以使用map指令通过此简单技巧为所有server块设置全局变量.您可以使用default关键字为地图值设置默认值.就像这个简单的例子一样:

So now, what does this mean for you? You can use the map directive to set a global variable for all server blocks with this simple trick. You can use the default keyword to set a default value for your map value. As in this simple example:

map $host $my_variable {
  default lalalala;
}

在此示例中，我们根据$host值计算$my_variable的值，但是实际上$host是什么都没有关系，因为我们将始终将 lalalala 设置为该值对于我们的变量，默认情况下，没有其他选项.现在，在代码中的所有地方，您将以与所有其他可用变量相同的方式使用$my_variable(例如，使用set指令创建的变量)，您将获得 lalalala

In this example we calculate the value of $my_variable on the $host value, but in fact it doesn't matter what $host is because we will always set lalalala as the value for our variable by default and without other options. Now everywhere in your code when you will use $my_variable in the same way as all other available variables (for example created with set directive) you will get value of lalalala

为什么这比仅使用set指令更好?正如文档所说，由于set指令 nginx设置指令仅可在server, location and if块内部访问，因此不能用于为许多server块创建全局变量.

And why is this better than simply using the set directive? Because the set directive, as doc says nginx set directive is only accessible inside server, location and if blocks, so it cannot be used to create global variable for a number of server blocks.

有关map指令的文档可在此处获得:地图指令

Docs about map directive are available here: map directive

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