#include "apue.h"static void	sig_pipe(int);		/* our signal handler */intmain(void){	int		n, fd1[2], fd2[2];	pid_t	pid;	char	line[MAXLINE];	if (signal(SIGPIPE, sig_pipe) == SIG_ERR)		err_sys("signal error");	if (pipe(fd1) < 0 || pipe(fd2) < 0)		err_sys("pipe error");	if ((pid = fork()) < 0) {		err_sys("fork error");	} else if (pid > 0) {							/* parent */		close(fd1[0]);		close(fd2[1]);		while (fgets(line, MAXLINE, stdin) != NULL) {			n = strlen(line);			if (write(fd1[1], line, n) != n)				err_sys("write error to pipe");			if ((n = read(fd2[0], line, MAXLINE)) < 0)				err_sys("read error from pipe");			if (n == 0) {				err_msg("child closed pipe");				break;			}			line[n] = 0;	/* null terminate */			if (fputs(line, stdout) == EOF)				err_sys("fputs error");		}		if (ferror(stdin))			err_sys("fgets error on stdin");		exit(0);	} else {									/* child */		close(fd1[1]);		close(fd2[0]);		if (fd1[0] != STDIN_FILENO) {			if (dup2(fd1[0], STDIN_FILENO) != STDIN_FILENO)				err_sys("dup2 error to stdin");			close(fd1[0]);		}		if (fd2[1] != STDOUT_FILENO) {			if (dup2(fd2[1], STDOUT_FILENO) != STDOUT_FILENO)				err_sys("dup2 error to stdout");			close(fd2[1]);		}		if (execl("./add2", "add2", (char *)0) < 0)			err_sys("execl error");	}	exit(0);}static voidsig_pipe(int signo){	printf("SIGPIPE caught\n");	exit(1);}