Detailed explanation of various uses of xargs command techniques in Linux

xargs is a filter for passing parameters to commands, and is also a tool for combining multiple commands. The following article mainly introduces to you the relevant information about the usage of xargs command in linux. Friends who need it can refer to it. Let’s take a look with the editor.

Preface

The xargs command reformats the received data and then provides it as a parameter to other commands. The xargs command is introduced below. Let’s take a look at various techniques for using commands.

1. Convert multi-line input into single-line input:

[root@host1 test]# echo -e "1 2 3 4 5 \n6 7 8 \n9 10 11 12" >example.txt
[root@host1 test]# cat example.txt 
1 2 3 4 5 
6 7 8 
9 10 11 12
[root@host1 test]# cat example.txt |xargs 
1 2 3 4 5 6 7 8 9 10 11 12

Convert single-line input into multi-line output:

[root@host1 test]# cat example.txt | xargs -n 3
1 2 3
4 5 6
7 8 9
10 11 12

Customize the delimiter for conversion (the default delimiter is a space):

[root@host1 test]# echo "Hello:Hello:Hello:Hello" | xargs -d : -n 2
Hello Hello
Hello Hello

2. Use it in the script:

[root@host1 test]# cat echo.sh 
#!/bin/bash
echo $* '^-^'

When the parameters are passed to echo.sh, it will print out these parameters and end with "^-^":

[root@host1 test]# echo -e "Tom\nHarry\nJerry\nLucy" > args.txt
[root@host1 test]# cat args.txt | xargs bash echo.sh 
Tom Harry Jerry Lucy ^-^
[root@host1 test]# cat args.txt | xargs -n 2 bash echo.sh 
Tom Harry ^-^
Jerry Lucy ^-^

In the above example, we The parameter sources are put into the args.txt file, but in addition to these parameters, we also need some fixed parameters, such as:

[root@host1 test]# bash echo.sh Welcome Tom 
Welcome Tom ^-^

During the execution of the above command, Tom is the variable , the rest are constants, we can extract the parameters from "args.txt" and provide them to the command in the following way:

[root@host1 test]# bash echo.sh Welcome Tom 
[root@host1 test]# bash echo.sh Welcome Herry
[root@host1 test]# bash echo.sh Welcome Jerry
[root@host1 test]# bash echo.sh Welcome Lucy

At this time we need to use xargs -I command:

[root@host1 test]# cat args.txt | xargs -I {} bash echo.sh Welcome {} 
Welcome Tom ^-^
Welcome Harry ^-^
Welcome Jerry ^-^
Welcome Lucy ^-^

-I {} specifies the replacement of string. For each command parameter, the string {} will be replaced by the parameters read from stdin. ,

When -I is used, the command is executed in a loop. If there are 4 parameters, the command will be executed 4 times together with {}, in each execution {} will be replaced with the corresponding parameters.

3. Use with find

xargs and find are a very good combination, but we usually use it in the wrong way Ways to use them, such as:

[root@host1 test]# find . -type f -name "*.txt" -print | xargs rm -f

This is dangerous, sometimes delete unnecessary files, if the file name contains a space character (' '), then xargs It is possible to think that they are delimiters (e.g. file text.txt will be mistaken for file and text.txt by xargs).

If we want to use the output of find as the input of xargs, we must use -print0 in conjunction with find to separate the output with the characters null ('\0'), and use find to find out All .txt files, and then use xargs to delete these files:

[root@host1 test]# find . -type f -name "*.txt" -print0 | xargs -0 rm -f

This way you can delete all .txt files, xargs -0 Use \0 as the input delimiter.

4. Use the while statement and subshell

[root@host1 test]# cat files.txt | (while read arg ;do cat $arg;done)

This command is equivalent to:

[root@host1 test]# cat files.txt | xargs -I {} cat {}

In while loop, cat $arg can be replaced with any number of commands, so that we can execute multiple commands on the same parameter, or we can use The output is passed to other commands. This technique is suitable for a variety of problem scenarios. Multiple commands within subshellOperator can be run as a whole.

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