Question

The system() function seems to be returning 128 times the exit code I get from the process it’s evoking.

From the man page:

RETURN VALUE
The value returned is -1 on error (e.g., fork(2)
failed), and the return status of the command other‐
wise.

Here is what I’ve got.

$ ls tinker.c
tinker.c
$ echo $?
0
$ ls notexisting
ls: cannot access notexisting: No such file or directory
$ echo $?
2
$ cat tinker.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    printf("%d\n", system("ls tinker.c"));
    printf("%d\n", system("ls notexisting"));
    return 0;
}
$ gcc tinker.c -o tinker
$ ./tinker 
tinker.c
0
ls: cannot access notexisting: No such file or directory
512

The first call indicates that I’m not getting failures but the return codes look nothing like what I’m reading from the man page. What’m I doing wrong?

Answer 1

From POSIX system(3):

If command is not a null pointer, system() shall return the termination status of the command language interpreter in the format specified by waitpid().

To get the return code, you need to use the WEXITSTATUS macro.