유닉스 쉘 구현할 때 파이프 기능구현 질문있습니다

int join(char *ang[]){
	pid_t pid[npipe+1];
	int p[npipe][2], status;
	int i,j;
	char **com[10];
 
	ang[pipe_p[0]] = NULL;
	com[0] = ang;
//printf("%s11\n", com[0][0]);
	for(i=1; i<npipe + 1; i++){
		if(pipe_p[i] != 0) ang[pipe_p[i]] = NULL;
		com[i] = ang+(pipe_p[i-1]+1);
	}
 
	for(i=0; i<npipe; i++){  //  PIPE생성
		if(pipe(p[i]) == -1) fatal("pipe call in join");
	}
 
	for(i=0; i<=npipe; i++){
 
	switch(pid[i] = fork()){  //  자식이 손자를 만든다
		case -1:
			fatal("2nd fork call in join");
		case 0:  //  쓰는 프로세스
			if(i == 0){
				dup2(p[i][1],1);
			//	for(j=0; j<=npipe; j++){
					close(p[i][0]);
					close(p[i][1]);
			//	}
				execvp(com[i][0], com[i]);
 
				fatal("1st execvp call in join");
			}
 
			else if(i==npipe){
				dup2(p[i-1][0],0);
			//	for(j=0; j<=npipe; j++){
					close(p[i][0]);
					close(p[i][1]);
			//	}
 
				execvp(com[i][0], com[i]);
 
				fatal("2st execvp call in join");
			}
			else{
				dup2(p[i-1][0],0);
				dup2(p[i][1],1);
 
				for(j=0; j<=npipe; j++){
					close(p[j][0]);
					close(p[j][1]);
				}
 
				execvp(com[i][0], com[i]);
 
				fatal("1st execvp call in join");
			}
	}  //  end switch
	}  //  end for
 
	for(j=0; j<npipe; j++){
		close(p[j][0]);
		close(p[j][1]);
	}
/*for(i=0; i<npipe+1; i++){
 printf("%d\n", pid[i]);
}*/
	while(waitpid(pid[npipe], &status, WNOHANG == 0)) sleep(1);
	return 0;
}