ch09-pipeline.c

linux编程精髓 源代码

/* ch09-pipeline.c --- fork two processes into their own pipeline.
		       Minimal error checking for brevity. */

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

int pipefd[2];

extern void left_child(void), right_child(void);

/* main --- fork children, wait for them to finish */

int main(int argc, char **argv)
{
	pid_t left_pid, right_pid;
	pid_t ret;
	int status;

	if (pipe(pipefd) < 0) {		/* create pipe, very first thing */
		perror("pipe");
		exit(1);
	}

	if ((left_pid = fork()) < 0) {	/* fork left-hand child */
		perror("fork");
		exit(1);
	} else if (left_pid == 0)
		left_child();

	if ((right_pid = fork()) < 0) {	/* fork right-hand child */
		perror("fork");
		exit(1);
	} else if (right_pid == 0)
		right_child();

	close(pipefd[0]);		/* close parent's copy of pipe */
	close(pipefd[1]);

	while ((ret = wait(& status)) > 0) {	/* wait for children */
		if (ret == left_pid)
			printf("left child terminated, status: %x\n", status);
		else if (ret == right_pid)
			printf("right child terminated, status: %x\n", status);
		else
			printf("yow! unknown child %d terminated, status %x\n",
				ret, status);
	}

	return 0;
}

/* left_child --- do the work for the left child */

void left_child(void)
{
	static char *left_argv[]  = { "echo", "hi", "there", NULL };

	close(pipefd[0]);
	close(1);
	dup(pipefd[1]);
	close(pipefd[1]);

	execvp("echo", left_argv);
	_exit(errno == ENOENT ? 127 : 126);
}

/* right_child --- do the work for the right child */

void right_child(void)
{
	static char *right_argv[] = { "sed", "s/hi/hello/g", NULL };

	close(pipefd[1]);
	close(0);
	dup(pipefd[0]);
	close(pipefd[0]);

	execvp("sed", right_argv);
	_exit(errno == ENOENT ? 127 : 126);
}