$2\mathrm{.}3$ Task $3$: Environment Variables and execve$()$

In this task, we study howenvironmentvariables are affected when a newprogramisexecutedviaexecve$().$

The function execve$()$ calls a system call to load a new command and execute it; this function never re

turns. No new process is created; instead, the calling process$$s text, data, bss$,$ and stack are overwritten by

that of the program loaded. Essentially, execve$()$ runs the new program inside the calling process. We

are interested in what happens to the environment variables; are they automatically inherited by the new

program?

Step $1.$ Please compile and run the following program, and describe your observation. This program

simply executes a program called $/$usr$/$bin$/$env$,$ which prints out the environment variables of the

current process.

Listing $2$: myenv.c

#include

extern char $**$environ;

int main$()$

$\{$

char $*$argv$[2]$;

argv$[0]="/$usr$/$bin$/$env$"$;

argv$[1]=$ NULL;

execve$("/$usr$/$bin$/$env$",$ argv, NULL$)$;

$$

return $0$ ;

$\}$

Step $2.$ Change the invocation of execve$()$ in Line $$ to the following; describe your observation.

execve$("/$usr$/$bin$/$env$",$ argv, environ$)$;

Step $3.$ Please draw your conclusion regarding how the new program gets its environment variables.