#include <fcntl.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/wait.h>
int main(int argc, char *argv[])
{
	pid_t p;
	int t[2];
	assert(pipe(t) == 0);

	p = fork();

	if (p == 0){
		close(t[0]);
		dup2(t[1],STDOUT_FILENO);
		close(t[1]);
		execlp("ls","ls",NULL);
		assert(0);
	}

	p = fork();

	if (p == 0){
		int fd = open("output.txt",O_WRONLY|O_CREAT|O_APPEND,0644);
		assert(fd != -1);

		close(t[1]);
		dup2(t[0],STDIN_FILENO);
		close(t[0]);
		dup2(fd,STDOUT_FILENO);
		close(fd);
		execlp("wc","wc",NULL);
		assert(0);

	}

	close(t[0]);
	close(t[1]);

	wait(NULL);
	wait(NULL);

	return 0;
}