#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>

// Examples of the 6 'exec' commands

// Note that you can only use one of these commands per run, because each
// one will replace this entire program.

// There is one man page for 'execve' and one (w/ many aliases) for
// the other five. The other five are in fact aliases for execve.

int main(int argc, char *argv[])
{
    int ret;

    // the command and its args, followed by a 0
    char *cmd[] = { "ls", "-Als", 0 };

    // the environment, followed by a 0
    char *env[] = { "HOME=/usr/home", "LOGNAME=home", 0 };


    // These 3 have a hard-coded command w/ its arguments
    //   (terminated by a 0)
    // The one ending in 'e' also specifies the environment
    // The one ending in 'p' doesn't need to give the full path
    //   because the system will look up the PATH variable

  ret = execl  ("/bin/ls", "ls", "-Als", 0);
  ret = execle ("/bin/ls", "ls", "-Als", 0, env);
  ret = execlp ("ls",      "ls", "-Als", 0);

    // These 3 use the cmd array instead of a hard-coded command
    // Same notes as above about 'e' and 'p'

  ret = execv  ("/bin/ls", cmd);
  ret = execve ("/bin/ls", cmd, env);
  ret = execvp ("ls", cmd);



  // Detailed definitions of each function:

  //  execl() executes the ls command, specifying the
  //  pathname of the executable (/bin/ls) and using arguments
  //  supplied directly to the command

  //  execle() specifies the environment for the new process
  //  image using the env argument.

  //  execlp() searches for the location of the ls command in the
  //  directories specified by the PATH environment variable.

  // execv() passes arguments to the ls command in the cmd array.

  // execve() passes arguments to the ls command in the cmd array,
  // and specifies the environment for the new process image using
  // the env argument.

  // execvp() searches for the location of the ls command in the
  // directories specified by the PATH environment variable, and
  // passes arguments to the ls command in the cmd array.

}