Why doesn't unistd.h execvpe work on macOS? - c

Question

I have the following code in which I'm executing another program within a program in C using execve from unistd.h:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char** argv) {
// char *env_init[] = {"USER=unknown", "PATH=/tmp", NULL};
char* username = argv[1];
char* program = argv[2];
printf("username: %s\n", username);
printf("program: %s\n", program);
if (execvp(program, argv + 2) < 0)
printf("error");
return 0;
}
and it runs fine. But when I try to put in the environment in the program and run the program using execvpe like so:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char** argv) {
char *env_init[] = {"USER=unknown", "PATH=/tmp", NULL};
char* username = argv[1];
char* program = argv[2];
printf("username: %s\n", username);
printf("program: %s\n", program);
if (execvpe(program, argv + 2, env_init) < 0)
printf("error");
return 0;
}
I get the following error:
runas.c:18:7: error: implicit declaration of function 'execvpe' is invalid in C99
[-Werror,-Wimplicit-function-declaration]
if (execvpe(program, argv + 3, env_init) < 0)
How do I fix this?

Answer 1

As you can read in the man page for execvpe:
The execvpe() function is a GNU extension
It's not a POSIX function and macOS doesn't necessarily support it, nor is it portable.
If you run man execvpe you will get the message:
No manual entry for execvpe
This indicates that macOS (at least on my machine) doesn't support this extension.
You might get it by using an alternative libc to the one used natively, but it's better to simply use one of the (portable) POSIX functions.
Good Luck!
P.S.
FYI: macOS supports any of the following: execl, execle, execlp, execv, execvp, execvP