管道与重定向到流程 [英] Pipe vs redirect into process

问题描述

寻找一些 bash-expert 的解释.下一个之间的确切区别是什么

Looking for some bash-expert explanation. What is the exact difference between of the next

command1 | command2

例如经典管道，其中command1的标准输出重定向到command2的标准输入，例如

e.g. classic pipe where the stdout of command1 is redirected to the stdin of command2, e.g.

• bash自身分叉两次
• 更改文件描述符
• 执行comman1和command2

和

command1 > >(command2)

结果(和bash动作)相同...

where the result (and the bash actions) are the same...

至少我从

find . -print0 | xargs -0 -n1 -I% echo =%=

和

find . -print0 > >(xargs -0 -n1 -I% echo =%=)

是>>(命令)只能说" | "吗?还是不，我错过了什么?

Is the > >(command) only the longer way saying |? Or not, and I missed something?

推荐答案

要实现

command1 | command2

外壳程序在父进程中创建一个管道，并将其一端连接到command1的输出(fd 1；它使用dup或dup2)，另一端连接到command2的输入(fd 0).

the shell creates a pipe in the parent process and attaches one end of it to the output (fd 1; it uses dup or dup2) of command1, and the other end to the input (fd 0) of command2.

要实现

command1 > >(command 2)

，shell将创建一个FIFO.它将command2的stdin附加到FIFO(通常使用O_WRONLY标志打开)，并将FIFO的名称作为位置参数传递给command1.您可以使用 echo>(true)轻松地看到这一点.

, the shell creates a FIFO. It attaches the command2's stdin to the FIFO (with open using the O_WRONLY flag, usually) and it passes the name of the FIFO as a positional argument to command1. You can easily see this by using echo >(true).

如果使用

> >(foo)

，则这些形式确实非常相似.但是，过程替换机制更强大.例如，您可以执行以下操作:

these forms are indeed very similar. However, the process subsititution mechanism is more powerful. For example you get do this kind of thing:

diff -u  <(curl 'http://www.a.example.com/')  <(curl 'http://www.b.example.com/')

您不能使用管道执行此操作-您不能有两个标准输入.

You can't do that with pipes - you can't have two standard inputs.

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