Linux Basics: Xargs command

Brief introduction

Xargs can convert input content (typically passed through the command line pipeline) into parameters for subsequent commands, typically using:

1. Command combination: In particular, some commands do not support pipeline input, such as ls .
2. Avoid parameters that are too long: Xargs can be used -nx to group parameters to avoid too long parameters.

Use the following syntax

Usage: xargs [OPTION]... COMMAND INITIAL-ARGS...Run COMMAND with arguments INITIAL-ARGS and more arguments read from input.

Getting Started examples

First, create a test file

touch a.js b.js c.js

Next, run the following command:

ls|xargs ls -al

The output is as follows:

-rw-r--r--  1 a  wheel  0 12 18 16:18 a.js-rw-r--r--  1 a  wheel  0 12 18 16:18 b.js-rw-r--r--  1 a  wheel  0 12 18 16:18 c.js

Command explanation:

1. First, ls *.js the output is a.js b.js c.js .
2. The input parameters that will be a.js b.js c.js taken through xargs the pipeline.
3. xargsAfter the command receives the input parameter, parses the argument, breaks the space/line break as a delimiter, splits into several parameters, here becomes a.js , b.js , c.js .
4. xargsThe split arguments are passed to subsequent commands as arguments for subsequent commands, that is, to make up such a command ls -al a.js b.js c.js .

You can add a -t parameter to print the command before executing the command that follows it.

ls|xargs -t ls -al

The output is as follows, you can see a line ls -al a.js b.js c.js of content, this is the actual running command.

ls -al a.js b.js c.js-rw-r--r--  1 a  wheel  0 12 18 16:18 a.js-rw-r--r--  1 a  wheel  0 12 18 16:18 b.js-rw-r--r--  1 a  wheel  0 12 18 16:18 c.js

Example: Parameter substitution

Sometimes, we need to use the original parameters, which can be passed through parameters -i or -I implementations. The parameters are described below

  -I R                         same as --replace=R (R must be specified)  -i,--replace=[R]             Replace R in initial arguments with names                               readfromstandardinputIfRis                               unspecified{}

As an example, add the suffix to all the .js end files .backup . -I ‘{}‘indicates that the following command line is replaced with the {} previously parsed argument.

ls|xargs'{}'{}{}.backup

The following commands are expanded:

mv a.js a.js.backupmv b.js b.js.backupmv c.js c.js.backup

Example: Parameter grouping

The command line has a limit on the maximum length of the parameter, and Xargs -nx solves the problem by grouping the parameters.

First, create 4 files to experiment with.

touch a.js b.js c.js d.js

Then run the following command:

ls|xargs -t -n2 ls -al

The output is as follows, -n2 indicating that the parameters are set in groups of 2 and passed to the following command.

ls-rw-r--r-- 1 root root 0 Dec 18 16:52 a.js-rw-r--r-- 1 root root 0 Dec 18 16:52 b.jsls-rw-r--r-- 1 root root 0 Dec 18 16:52 c.js-rw-r--r-- 1 root root 0 Dec 18 16:52 d.js

Example: Special file name

Sometimes, a file name may have special characters, such as a space in the file name below.

touch 'hello 01.css' 'hello 02.css'

The previous command will cause an error because it xargs is separated by a space/line break, and the expected behavior occurs.

# 命令find'*.css'|xargs -t ls -al#输出ls# 展开后的命令ls: cannot access ./hello: No such file or directoryls: cannot access 01.css: No such file or directoryls: cannot access ./hello: No such file or directoryls: cannot access 02.css: No such file or directory

xargsThis is the way to solve the problem.

1. -print0: tells the find command, after the output file name, to follow the NULL character, not the line break;
2. -0: Tell xargs , NULL as a parameter delimiter;

find'*.css'|xargs -0 -t ls -al

Example: Log backup

Back up logs from 7 days ago to a specific directory

find|xargs'{}'{} /tmp/otc-svr-logs/

RELATED LINKS

Https://craftsmanbai.gitbooks.io/linux-learning-wiki/content/xargs.html

Http://wiki.jikexueyuan.com/project/shell-learning/xargs.html

Linux Basics: Xargs command