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[translated] 20140928 How to use xargs command in Linux.md

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How to use xargs command in Linux
================================================================================
Have you ever been in the situation where you are running the same command over and over again for multiple files? If so, you know how tedious and inefficient this can feel. The good news is that there is an easier way, made possible through the xargs command in Unix-based operating systems. With this command you can process multiple files efficiently, saving you time and energy. In this tutorial, you will learn how to execute a command or script for multiple files at once, avoiding the daunting task of processing numerous log files or data files individually.
There are two ingredients for the xargs command. First, you must specify the files of interest. Second, you must indicate which command or script will be executed for each of the files you specified.
This tutorial will cover three scenarios in which the xargs command can be used to process files located within several different directories:
1. Count the number of lines in all files
1. Print the first line of specific files
1. Process each file using a custom script
Consider the following directory named xargstest (the directory tree can be displayed using the tree command with the combined -i and -f options, which print the results without indentation and with the full path prefix for each file):
$ tree -if xargstest/
![](https://farm3.staticflickr.com/2942/15334985981_ce1a192def.jpg)
The contents of each of the six files are as follows:
![](https://farm4.staticflickr.com/3882/15346287662_a3084a8e4f_o.png)
The **xargstest** directory, its subdirectories and files will be used in the following examples.
### Scenario 1: Count the number of lines in all files ###
As mentioned earlier, the first ingredient for the xargs command is a list of files for which the command or script will be run. We can use the find command to identify and list the files that we are interested in. The **-name 'file??'** option specifies that only files with names beginning with "file" followed by any two characters will be matched within the xargstest directory. This search is recursive by default, which means that the find command will search for matching files within xargstest and all of its sub-directories.
$ find xargstest/ -name 'file??'
----------
xargstest/dir3/file3B
xargstest/dir3/file3A
xargstest/dir1/file1A
xargstest/dir1/file1B
xargstest/dir2/file2B
xargstest/dir2/file2A
We can pipe the results to the sort command to order the filenames sequentially:
$ find xargstest/ -name 'file??' | sort
----------
xargstest/dir1/file1A
xargstest/dir1/file1B
xargstest/dir2/file2A
xargstest/dir2/file2B
xargstest/dir3/file3A
xargstest/dir3/file3B
We now need the second ingredient, which is the command to execute. We use the wc command with the -l option to count the number of newlines in each file (printed at the beginning of each output line):
$ find xargstest/ -name 'file??' | sort | xargs wc -l
----------
1 xargstest/dir1/file1A
2 xargstest/dir1/file1B
3 xargstest/dir2/file2A
4 xargstest/dir2/file2B
5 xargstest/dir3/file3A
6 xargstest/dir3/file3B
21 total
You'll see that instead of manually running the wc -l command for each of these files, the xargs command allows you to complete this operation in a single step. Tasks that may have previously seemed unmanageable, such as processing hundreds of files individually, can now be performed quite easily.
### Scenario 2: Print the first line of specific files ###
Now that you know the basics of how to use the xargs command, you have the freedom to choose which command you want to execute. Sometimes, you may want to run commands for only a subset of files and ignore others. In this case, you can use the find command with the -name option and the ? globbing character (matches any single character) to select specific files to pipe into the xargs command. For example, if you want to print the first line of all files that end with a "B" character and ignore the files that end with an "A" character, use the following combination of the find, xargs, and head commands (head -n1 will print the first line in a file):
$ find xargstest/ -name 'file?B' | sort | xargs head -n1
----------
==> xargstest/dir1/file1B <==
one
==> xargstest/dir2/file2B <==
one
==> xargstest/dir3/file3B <==
one
You'll see that only the files with names that end with a "B" character were processed, and all files that end with an "A" character were ignored.
### Scenario 3: Process each file using a custom script ###
Finally, you may want to run a custom script (in Bash, Python, or Perl for example) for the files. To do this, simply substitute the name of your custom script in place of the wc and head commands shown previously:
$ find xargstest/ -name 'file??' | xargs myscript.sh
The custom script **myscript.sh** needs to be written to take a file name as an argument and process the file. The above command will then invoke the script for every file found by find command.
Note that the above examples include file names that do not contain spaces. Generally speaking, life in a Linux environment is much more pleasant when using file names without spaces. If you do need to handle file names with spaces, the above commands will not work, and should be tweaked to accommodate them. This is accomplished with the -print0 option for find command (which prints the full file name to stdout, followed by a null character), and -0 option for xargs command (which interprets a null character as the end of a string), as shown below:
$ find xargstest/ -name 'file*' -print0 | xargs -0 myscript.sh
Note that the argument for the -name option has been changed to 'file*', which means any files with names beginning with "file" and trailed by any number of characters will be matched.
### Summary ###
After reading this tutorial you will understand the capabilities of the xargs command and how you can implement this into your workflow. Soon you'll be spending more time enjoying the efficiency offered by this command, and less time doing repetitive tasks. For more details and additional options you can read the xargs documentation by entering the 'man xargs' command in your terminal.
--------------------------------------------------------------------------------
via: http://xmodulo.com/xargs-command-linux.html
作者：[Joshua Reed][a]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
[a]:http://xmodulo.com/author/joshua

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如何在Linux里使用xargs命令
================================================================================
你是否遇到过这样的情况，需要一遍又一遍地对多个文件执行同样的操作？如果有过，那你肯定会深有感触这是多么的无聊和效率低下。还好有种简单的方式，可以在类Unix操作系统中使用xargs命令解决这个烦恼。通过这个命令你可以有效地处理多个文件，节省你的时间和精力。在这篇教程中，你可以学到如何一次性对多个文件执行命令或脚本操作，再也不用担心像单独处理无数个日志或数据文件那样吓人的任务了。
xargs命令有两个要点。第一，你必须列出目标文件。第二，你必须指定对每个文件需要执行的命令或脚本。
这篇教程会涉及三个应用场景，xargs命令被用来处理分布在不同目录下的文件：
1. 计算所有文件的行数
1. 打印指定文件的第一行
1. 对每个文件执行一个自定义脚本
请看下面这个叫xargstest的目录（用tree命令以及-i和-f选项显示了目录树结构，这样可以避免缩进显示而且每个文件都会带有完整路径）：
$ tree -if xargstest/
![](https://farm3.staticflickr.com/2942/15334985981_ce1a192def.jpg)
这六个文件的内容分别如下：
![](https://farm4.staticflickr.com/3882/15346287662_a3084a8e4f_o.png)
这个**xargstest**目录，以及它包含的子目录和文件将用在下面的例子中。
### 场景1：计算所有文件的行数 ###
就像之前提到的，使用xargs命令的第一个要点是一个用来运行命令或脚本的文件列表。我们可以用find命令来确定和列出目标文件。选项**-name 'file??'**指定了xargstest目录下那些名字以"file"开头并跟随两个任意字符的文件才是匹配的。这个搜索默认是递归的，意思是find命令会在xargstest和它的子目录下搜索匹配的文件。
$ find xargstest/ -name 'file??'
----------
xargstest/dir3/file3B
xargstest/dir3/file3A
xargstest/dir1/file1A
xargstest/dir1/file1B
xargstest/dir2/file2B
xargstest/dir2/file2A
我们可以通过管道把结果发给sort命令让文件名按顺序排列：
$ find xargstest/ -name 'file??' | sort
----------
xargstest/dir1/file1A
xargstest/dir1/file1B
xargstest/dir2/file2A
xargstest/dir2/file2B
xargstest/dir3/file3A
xargstest/dir3/file3B
然后我们需要第二个部分，就是需要执行的命令。我们使用带有-l选项的wc命令来计算每个文件包含的换行符数目（会在输出的每一行的前面打印出来）：
$ find xargstest/ -name 'file??' | sort | xargs wc -l
----------
1 xargstest/dir1/file1A
2 xargstest/dir1/file1B
3 xargstest/dir2/file2A
4 xargstest/dir2/file2B
5 xargstest/dir3/file3A
6 xargstest/dir3/file3B
21 total
可以看到，不用对每个文件手动执行一次wc -l命令，而xargs命令可以让你在一步里完成所有操作。那些之前看起来无法完成的任务，例如单独处理数百个文件，现在可以轻松进行了。
### 场景2：打印指定文件的第一行 ###
既然对xargs命令的使用已经有一点基础了，你可以自由选择执行什么命令。有时，你也许希望只对一部分文件执行操作而忽略其他的。在这种情况下，你可以使用find命令的-name选项以及?通配符（匹配任意单个字符）来选中特定文件并通过管道输出给xargs命令。举个例子，如果你想打印以“B”字符结尾的文件而忽略以“A”结尾的文件的第一行，可以使用下面的find、xargs和head命令组合来完成（head -n1会打印一个文件的第一行）：
$ find xargstest/ -name 'file?B' | sort | xargs head -n1
----------
==> xargstest/dir1/file1B <==
one
==> xargstest/dir2/file2B <==
one
==> xargstest/dir3/file3B <==
one
你将看到只有以“B”结尾的文件会被处理，而所有以“A”结尾的文件都被忽略了。
### 场景3：对每个文件执行一个自定义脚本 ###
最后，你也许希望对一些文件执行一个自定义脚本（例如Bash、Python或是Perl）。要做到这个，只要简单地把你的自定义脚本名字替换掉之前例子中的wc和head命令就好了：
$ find xargstest/ -name 'file??' | xargs myscript.sh
自定义脚本**myscript.sh**需要写成接受一个文件名作为参数并处理这个文件。上面的命令将为find命令找到的每个文件分别调用脚本。
注意一下上面的例子中的文件名并没有包含空格。通常来说，在Linux环境下操作没有空格的文件名会舒服很多。如果你实在是需要处理名字中带有空格的文件，上边的命令就不能用了，需要稍微处理一下来让它可以被接受。这可以通过find命令的-print0选项（它会打印完整的文件名到标准输出，并以空字符结尾），以及xargs命令的-0选项（它会以空字符作为字符串结束标记）来实现，就像下面的例子：
$ find xargstest/ -name 'file*' -print0 | xargs -0 myscript.sh
注意一下，-name选项所跟的参数已经改为'file\*'，意思是所有以"file"开头而结尾可以是任意字符的文件都会被选中。
### 总结 ###
在看完这篇教程后你应该会理解xargs命令的作用，以及如何应用到自己的工作中。很快你就可以有时间享受这个命令所带来的高效率，而不哟给你花时间在一些重复的任务上了。想了解更详细的信息以及更多的选项，你可以在终端中输入'man xargs'命令来查看xargs的文档。
--------------------------------------------------------------------------------
via: http://xmodulo.com/xargs-command-linux.html
作者：[Joshua Reed][a]
译者：[zpl1025](https://github.com/zpl1025)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
[a]:http://xmodulo.com/author/joshua