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translating---geekpi
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An introduction to pipes and named pipes in Linux
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======
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In Linux, the `pipe` command lets you sends the output of one command to another. Piping, as the term suggests, can redirect the standard output, input, or error of one process to another for further processing.
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The syntax for the `pipe` or `unnamed pipe` command is the `|` character between any two commands:
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`Command-1 | Command-2 | …| Command-N`
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Here, the pipe cannot be accessed via another session; it is created temporarily to accommodate the execution of `Command-1` and redirect the standard output. It is deleted after successful execution.
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In the example above, contents.txt contains a list of all files in a particular directory—specifically, the output of the ls -al command. We first grep the filenames with the "file" keyword from contents.txt by piping (as shown), so the output of the cat command is provided as the input for the grep command. Next, we add piping to execute the awk command, which displays the 9th column from the filtered output from the grep command. We can also count the number of rows in contents.txt using the wc -l command.
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A named pipe can last until as long as the system is up and running or until it is deleted. It is a special file that follows the [FIFO][1] (first in, first out) mechanism. It can be used just like a normal file; i.e., you can write to it, read from it, and open or close it. To create a named pipe, the command is:
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```
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mkfifo <pipe-name>
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```
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This creates a named pipe file that can be used even over multiple shell sessions.
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Another way to create a FIFO named pipe is to use this command:
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```
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mknod p <pipe-name>
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```
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To redirect a standard output of any command to another process, use the `>` symbol. To redirect a standard input of any command, use the `<` symbol.
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As shown above, the output of the `ls -al` command is redirected to `contents.txt` and inserted in the file. Similarly, the input for the `tail` command is provided as `contents.txt` via the `<` symbol.
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Here, we have created a named pipe, `my-named-pipe`, and redirected the output of the `ls -al` command into the named pipe. We can the open a new shell session and `cat` the contents of the named pipe, which shows the output of the `ls -al` command, as previously supplied. Notice the size of the named pipe is zero and it has a designation of "p".
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So, next time you're working with commands at the Linux terminal and find yourself moving data between commands, hopefully a pipe will make the process quick and easy.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/18/8/introduction-pipes-linux
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作者：[Archit Modi][a]
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选题：[lujun9972](https://github.com/lujun9972)
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://opensource.com/users/architmodi
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[1]:https://en.wikipedia.org/wiki/FIFO_(computing_and_electronics)
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@ -0,0 +1,60 @@
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介绍 Linux 中的管道和命名管道
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======
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在 Linux 中，`pipe` 能让你将一个命令的输出发送给另一个命令。管道，如它的名称那样，能重定向一个进程的标准输出、输入、和错误到另一个进程，以便于进一步处理。
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`pipe` 或者 `unnamed pipe` 命令的语法是在两个命令之间加上 `|` 字符：
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`Command-1 | Command-2 | …| Command-N`
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这里，管道不能通过另一个会话访问；它被临时创建用于接收 `Command-1` 的执行并重定向标准输出。它在成功执行之后删除。
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在上面的示例中，contents.txt 包含特定目录中所有文件的列表 - 具体来说，就 是ls -al 命令的输出。我们首先通过管道（如图所示）使用 contents.txt 中的 “file” 关键字 grep 文件名，因此 cat 命令的输出作为 grep 命令的输入提供。接下来，我们添加管道来执行 awk 命令，该命令显示 grep 命令的过滤输出中的第 9 列。我们还可以使用 wc -l 命令计算 contents.txt 中的行数。
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只要系统启动并运行或直到它被删除，命名管道就可以持续使用。它是一个遵循 [FIFO][1]（先进先出）机制的特殊文件。它可以像普通文件一样使用。也就是，你可以写入，从中读取，然后打开或关闭它。要创建命名管道，命令为：
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```
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mkfifo <pipe-name>
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```
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这将创建一个命名管道文件，它甚至可以在多个 shell 会话中使用。
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创建 FIFO 命名管道的另一种方法是使用此命令：
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```
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mknod p <pipe-name>
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```
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`>` 符号。要重定向任何命令的标准输入，请使用 `<` 符号。
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如上所示，`ls -al` 命令的输出被重定向到 `contents.txt` 并插入到文件中。类似地，`tail` 命令的输入通过 `<` 符号从 `contents.txt` 读取。
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这里，我们创建了一个命名管道 `my-named-pipe`，并将 `ls -al` 命令的输出重定向到命名管道。我们可以打开一个新的 shell 会话并 `cat` 命名管道的内容，如前所述，它显示了 `ls -al`命令的输出。请注意，命名管道的大小为零，并有一副标志 “p”。
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因此，下次你在 Linux 终端上使用命令并在命令之间移动数据时，希望管道使过程快速简便。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/18/8/introduction-pipes-linux
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作者：[Archit Modi][a]
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选题：[lujun9972](https://github.com/lujun9972)
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://opensource.com/users/architmodi
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[1]:https://en.wikipedia.org/wiki/FIFO_(computing_and_electronics)
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