程序中的两个重定向 [英] Two redirect in program

问题描述

我尝试用C语言编写命令解释器.我必须创建dwo和三个重定向(例如ls | grep ^d | wc -l和ls -ps | grep / | pr -3 | more)

我有操作一个重定向的代码

    if(k==1)
{
  int pfds[2];
  pipe(pfds);
  child_pid = fork();
  if(child_pid==0)
  {       
    close(1);       
        dup(pfds[1]);   
        close(pfds[0]); 
        execlp(arg1[0], *arg1, NULL);
  }
  else 
  {
        close(0);      
        dup(pfds[0]);
        close(pfds[1]); 
        execlp(arg2[0], *arg2, NULL);
  }     
}

我的问题是如何使用pipe和fork进行两次和三次重定向?

我尝试仅使用一个管道来执行此操作，但这不起作用.

解决方案

您将不得不创建与转移"一样多的pipe变量. 然后创建命令列表.

如果您希望父进程离开，则可以为每个命令派生一个进程.否则少一遍.

对于第一个命令，dup或"dup2"仅用于STDOUT.

，并且对于最后一个命令dup或'dup2'仅适用于STDIN.

对于其余部分，对于STDIN和STDOUT都是dup或'dup2`.

您可以使用从第二倒数第二个倒数第二个for循环进行此操作.

例如: 外壳$> cat file.txt | grep'pattern1 | pattern2'| grep'pattern1'| wc -l <​​/p>

我假设您没有将父进程用于exec 因此，您将创建命令的列表/数组/向量.列表将具有所有4个命令. 在父进程本身中为每个命令创建4个管道.

运行一个循环进行4次迭代，每个循环用于一条命令.

• 分叉一个过程.
• 如果是父进程，请继续.
• 其他(孩子)
  • 仅对第一个命令(cat)使用dup/dup2 STDOUT.
  • dup/dup2仅STDIN用于最后一个命令(wc -l).
  • 否则要分别对STDIN和STDOUT进行dup/dup2.
  • 然后运行exec.

干杯:)

I try write a command interpreter in C. I must create dwo and three redirects (e.g. ls | grep ^d | wc -l and ls -ps | grep / | pr -3 | more)

I have code to operate one redirects

    if(k==1)
{
  int pfds[2];
  pipe(pfds);
  child_pid = fork();
  if(child_pid==0)
  {       
    close(1);       
        dup(pfds[1]);   
        close(pfds[0]); 
        execlp(arg1[0], *arg1, NULL);
  }
  else 
  {
        close(0);      
        dup(pfds[0]);
        close(pfds[1]); 
        execlp(arg2[0], *arg2, NULL);
  }     
}

My question is how make two and three redirects using pipe and fork?

I try do this using only one pipe but this in not work.

解决方案

you will have to create as many pipe variables as there are "diversion". then create a list of commands.

if you want parent process leave,you would fork a process for each command. otherwise one less.

for the very first command, dup or 'dup2` only for STDOUT.

and for the very last command dup or 'dup2` only for STDIN.

for the rest, dup or 'dup2` for STDIN and STDOUT both.

you can do this with a for loop from 2nd to second-last.

For Example: shell $> cat file.txt | grep 'pattern1|pattern2' | grep 'pattern1' | wc -l

I am assuming you are not using parent process for exec So, you would create a list/array/vector of commands. list would have all 4 commands. create 4 pipes for each commands in parent process itself.

run a loop for 4 iteration, each for a command.

• fork one process.
• if parent process, continue.
• else(child)
  • dup/dup2 only STDOUT for first command(cat).
  • dup/dup2 only STDIN for last command(wc -l).
  • dup/dup2 both STDIN and STDOUT otherwise.
  • then run exec.

CHEERS :)

这篇关于程序中的两个重定向的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！