c - 如何在 environ 中使用 execvp/execlp

Question

如何在 execlp 之前设置环境？

     #include <stdio.h>
    #include <unistd.h>
    #include <syslog.h>
//    Tried extern char **environ;

    int main (int argc, char *argv[]) 
    {
// Tried environ = -- gives compile error
        char** environ =
        {
            "foo=bar",
            "hello=world",
            0 // zero byte
        };

        //environ = ??
        execlp("env", "env", (char*)0);
    return 0;
    }

没有打印 foo = bar谢谢。

Answer 1

man execlp和 man environ将帮助:

The execle() and execvpe() functions allow the caller to specify the environment of the executed program via the argument envp. The envp argument is an array of pointers to null-terminated strings and must be terminated by a NULL pointer. The other functions take the environment for the new process image from the external variable environ in the calling process.

environ在 unistd.h 中声明作为extern ，您需要在调用 execlp() 之前填充变量.另请注意 environ 中的字符串预计格式为 key=value ;

#include <stdio.h>
#include <unistd.h>

// declare environ as extern
extern char** environ;

int main (int argc, char *argv[])
{

    // populate environ
    environ[0] = "foo=bar";
    environ[1] = NULL;

    // call execlp
    execlp("/usr/bin/env", "", (char *)0);

    return 0;
}