Performing arithmetics with execve from arguments passed by terminal

Question

Trying to understand how to perform an arithmetic operation from arguments passed from terminal and use them in execve ?

./myProgram 'echo "$1+$2=$(($1+$2))"' 3 5

this is suppose to give me an output of 8

what i've tried manually without argv :

pid_t pid;
char *parmList[] = {"sh", "-c", "echo $0 $1 + $2 1 2", NULL};
char *envParms[3] = {"1=1", "2=2", NULL};

if ((pid = fork()) == -1)
    perror("fork error");
else if (pid == 0)
{
    execve("/bin/sh", parmList, envParms);
    printf("Return not expected. Must be an execve error.n");
}

i get the $0 which is sh ✅

but $1 and $2 are not recognized ...what i am missing ?

In the shell `$1` is *not* the environment variable `1`. It is the first positional parameter. — William Pursell, Oct 23 '20 at 15:03

score 0 · Accepted Answer · answered Oct 23 '20 at 15:04

0

You don't want to be passing 1 and 2 in the environment. The shell wants them as positional parameters. So you could do:

char *parmList[] = {"sh", "-c", "echo $0 $1 + $2 1 2", "sh", "1", "2", NULL};

answered Oct 23 '20 at 15:04

William Pursell

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thank you so much, i've been stock on this for days ‍♂️ – ZeivRine Oct 23 '20 at 15:16

Performing arithmetics with execve from arguments passed by terminal

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