$2\mathrm{.}4$ Task $4$: Environment Variables and system$()$

In this task, we study how environment variables are affected when a new program is executed via the

system$()$ function. This function is used to execute a command, but unlike execve$(),$ which di

rectly executes a command, system$()$ actually executes $"/$bin$/$sh$-$c command", i$.$e$.,$ it executes

$/$bin$/$sh$,$ and asks the shell to execute the command.

If you look at the implementation of the system$()$ function, you will see that it uses execl$()$ to

execute $/$bin$/$sh; execl$()$ calls execve$(),$ passing to it the environment variables array. Therefore,

using system$(),$ the environment variables of the calling process is passed to the new program $/$bin$/$sh$.$

Please compile and run the following program to verify this.

#include

#include

int main$()$

$\{$

system$("/$usr$/$bin$/$env$")$;

return $0$ ;

$\}$