C语言 使用 dup2 进行管道
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Using dup2 for piping
提问by Rob Kearnes
How do I use dup2 to perform the following command?
如何使用 dup2 执行以下命令？
ls -al | grep alpha | more
回答by theprole
A Little example with the first two commands. You need to create a pipe with the pipe() function that will go between ls and grep and other pipe between grep and more. What dup2 does is copy a file descriptor into another. Pipe works by connecting the input in fd[0] to the output of fd[1]. You should read the man pages of pipe and dup2. I may try and simplify the example later if you have some other doubts.
前两个命令的一个小例子。您需要使用 pipe() 函数创建一个管道，该管道将在 ls 和 grep 之间以及 grep 和更多之间的其他管道之间进行。dup2 所做的是将一个文件描述符复制到另一个文件描述符中。管道的工作原理是将 fd[0] 的输入连接到 fd[1] 的输出。您应该阅读 pipe 和 dup2 的手册页。如果您有其他疑问，我稍后可能会尝试简化示例。
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#define READ_END 0
#define WRITE_END 1
int
main(int argc, char* argv[])
{
pid_t pid;
int fd[2];
pipe(fd);
pid = fork();
if(pid==0)
{
printf("i'm the child used for ls \n");
dup2(fd[WRITE_END], STDOUT_FILENO);
close(fd[WRITE_END]);
execlp("ls", "ls", "-al", NULL);
}
else
{
pid=fork();
if(pid==0)
{
printf("i'm in the second child, which will be used to run grep\n");
dup2(fd[READ_END], STDIN_FILENO);
close(fd[READ_END]);
execlp("grep", "grep", "alpha",NULL);
}
}
return 0;
}
回答by Ignacio Vazquez-Abrams
You would use pipe(2,3p)as well. Create the pipe, fork, duplicate the appropriate end of the pipe onto FD 0 or FD 1 of the child, then exec.
你也会用pipe(2,3p)。创建管道，分叉，将管道的适当末端复制到孩子的 FD 0 或 FD 1 上，然后执行。
