Question

Here I wrote a C program which executes hi.sh file using system call.

Here I used . ./hi.sh so I want to execute this script in the same shell
and then try to get environment variable using getenv function, but here I am getting different output from what I expected.

The hi.sh file contains

export TEST=10
return

Means when I run this hi.sh file using system call, its export TEST sets the value to 10 in same shell.
After this, I am trying to get this variable value but its given NULL value.

And if I run this script manually from console like . ./hi.sh then it works fine and I get 10 value of TEST using getenv("TEST") function.

Code:

#include <stdio.h>
int main()
{
    system(". ./hi.sh");
    char *errcode;
    char *env = "TEST";
    int errCode;    
    errcode = getenv(env);
    printf("Value is = %s\n",errcode);
    if (errcode != NULL) {
        errCode =atoi(errcode);
        printf("Value is = %d\n",errCode);
    }
}

output :

Value is = (null)

How can I export TEST variable in program shell? If system() executes commands in different shell then how can I use C program code to get an environment variable which is exported by the shell invoked via a system() call?

Answer 1

As usual, the man page does explain this, but you need to read it very carefully.

DESCRIPTION
       system()  executes a command specified in command by calling /bin/sh -c
       command, and returns after the command has been completed.  During exe‐
       cution  of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT
       will be ignored.

In other words, system() first starts /bin/sh, and then has /bin/sh start whatever command you want to execute.
So what happens here is that the TEST variable is exported to the /bin/sh shell the system() call implicitly started, but not to the program which called system().