Question 40558 in PHP Question posted in
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How does getenv() get the parameters of the http request parsed by nginx? – PHP

When writing CGI program for spawn-fcgi, use getenv() to get environment variables, that is, the parameters set by fastcgi_param command in fastcgi.conf. but when I use the env command output on the terminal in Linux, I can’t find the corresponding environment variable. Why?

fastcgi_param

Sets a parameter that should be passed to the FastCGI server. The value can contain text, variables, and their combination. These directives are inherited from the previous configuration level if and only if there are no fastcgi_param directives defined on the current level.

Since it says that these parameters are passed by nginx to the FastCGI server, how does getenv() get these parameters? I learned that getenv() is used to obtain environment variables. So did spawn-fcgi create these temporary environment variables according to fastcgi.conf when ngnix passed dynamic requests?

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Answers


  1. 0

    Each process has its own set of environment variables.

    When a new process gets created it inherits the environment variables from its parent process.

    The env command gets started by your terminal process, it inherits the terminal’s environment variables and that’s what it shows you.

    As you know, your terminal does not get started by spawn-fcgi. Although nobody knows which came first, the chicken or the egg, it’s fairly certain that your terminal process does not get started by spawn-fcgi. And that’s why your terminal does not show the environment variables that spawn-fcgi sets and are inherited by the processes that spawn-fcgi, itself, starts.

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  2. 0

    The fastcgi library directly modifies the environ variable of the program, simulating a new environment after accepting a request. See: https://github.com/FastCGI-Archives/fcgi2/blob/874b148dfeadf8ebadff89cf228e63f836e509a3/doc/FCGI_Accept.3

    After accepting a new request, FCGI_Accept assigns new values
    to the global variables stdin, stdout, stderr, and environ.
    After FCGI_Accept returns, these variables have the same
    interpretation as on entry to a CGI program.

    And https://pubs.opengroup.org/onlinepubs/7908799/xsh/environ.html

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