#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

/* Spawn a child process running a new program.
    PROGRAM is the name of the program to run.
    The path will be searched for this program.
    ARG_LIST is a NULL-terminated list of character
    strings to be passed as the program’s argument
    list. Returns the process ID of the spawned process. */

int spawn (char* program, char** arg_list) {
     pid_t child_pid;
     
     /* Duplicate this process. */
        child_pid = fork ();

           if (child_pid != 0)
            /* This is the parent process. */

           return child_pid; else {
            /* Now execute PROGRAM, searching for it in the path. */ 

                   execvp (program, arg_list);
                   /* The execvp function returns only if an error occurs. */ 

                   fprintf (stderr, "an error occurred in execvp\n");

                    abort ();
            }
}

int main () {
/* The argument list to pass to the "ls" command. */

char* arg_list[] = { "ls", /* argv[0], the name of the program. */ "-l", "/", NULL };
    /* The argument list must end with a NULL. */
    
    /* Spawn a child process running the "ls" command. Ignore the returned child process ID. */

    spawn ("ls", arg_list);
    printf ("Done with main program.\n");

    return 0;
}