Environment Variables

In the shell, the environment variables are a set of strings that stores the settings, for example, PATH variable stores the path searching setting and http_proxy sets the proxy server setting.

There are many ways to get environment variables. One of the ways is from the argument of main function.

/* Exec/env.c */
#include <stdio.h>
int main(int argc,char *argv[], char* envp[])
{ 
    int i; 
    for (i = 0; envp[i];i++) 
    { 
        printf("[%d]: %s\n",i,envp[i]);
    } 
    return 0;
}

Take a note of the main function parameter. There is an extra item of char * envp[]. This allows the program to retrieve the system environment variable.