// CS 450: Process example 1: fork, execlp
// version 2014-01-21 3:55 PM
//
#include <stdio.h>
#include <unistd.h> // for fork, execlp
#include <sys/wait.h>  // wait

int main()
{
    pid_t pid;      // Process id
    pid = fork();   // Fork child process

    // If pid < 0, an error occurred
    //
    if (pid < 0) {
        fprintf(stderr, "Fork Failed\n");
        return 1;
    }
    // If pid > 0, we're the parent.
    // Wait for the child to finish
    //
    else if (pid > 0) {
        wait(NULL);
        fprintf(stderr,
           "Parent says: Child process %d complete\n",
           pid );
    }
    // If pid = 0, we're the child.
    // Execute an ls command and quit
    //
    else  {
		fprintf(stderr,
		    "Child says: I'm %d\n", getpid());
        int error
            = execl("/bin/ls", "ls", "-l", NULL);

        // execl only returns if an error occurs
        // 
        fprintf(stderr,
           "Child says: exec returns with error %d\n", error);
    }
    return 0;  // parent finishes
}

// Sample output:
//
// Child says: I'm 1310
// total 40
// -rw-r--r--@ 1 jts  jts   734 Jan 21 15:52 Lec03_1_proc.py
// -rw-r--r--@ 1 jts  jts   820 Jan 22  2013 Lec03_2_proc.c
// -rwxr-xr-x  1 jts  jts  9036 Jan 21 15:55 a.out
// Parent says: Child process 1310 complete