// file: ls_SPOOL.c
//
// Synopsis: Simple illustration of redrection of output
//
// 	     Main process forks.
// 	     Child Process: 	(1) creats a file "SPOOL"
// 	     			(2) make SPOOL the standard output
// 	     			(3) close current standard output
// 	     			(4) exec "ls /etc ." (listing 2 dirs)
//	     Parent Process:	Wait on child
//
//	REMARK: THIS PROGRAM WORKS in CYGWIN and SOLARIS.
// Chee Yap

#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


main()
{  char *prog = "ls";
   char *argv[] = {"ls", "/etc", ".", NULL};
   int pid;
   printf("Before execute\n");
   pid = fork();
   if (pid==0) {
	   /* child */
	   int f;
	   if ((f=creat("SPOOL", S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH)) == -1)
		   perror("SPOOL");
	   dup2(f, STDOUT_FILENO);
	   close(f); // original not needed after dup2
	   execvp(prog, argv);
	   perror(prog);
   } else if (pid>0)
	   /* wait for child */
	   wait(NULL);
   else
	   perror("execute");
   printf("After execute\n");
   exit(0);
}