> For the complete documentation index, see [llms.txt](https://eric-lo.gitbook.io/lab4-process/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eric-lo.gitbook.io/lab4-process/process-execution/environment-variables.md).

# 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.

```c
/* 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.