[CENTOS] [Linux] How to use the echo command

Begin

Outputs the method that you often use for one of the Linux commands, the echo command.

What is the echo command?

This is a command that can do something like this.

--Display of character string on the screen --Display of command execution result --Output the string to a file --Add character string to file

How to use the echo command (example)

Display of character string

Displays the specified character string.

command


echo "String"

Command execution example

Execution example


[root@tspweb01 test]# echo aaaaa
aaaaa

Displaying command execution results

Displays the command execution result.

command


echo $?

--Command execution result

Execution result Contents
0 True(Command execution successful)
1 False(Command execution failed)
127 Command not found

Command execution example

--True (success)

Execution example(True)


[root@tspweb01 test]# true
[root@tspweb01 test]# echo $?
0

--False

Execution example(False)


[root@tspweb01 test]# false
[root@tspweb01 test]# echo $?
1

--Command not found

Execution example(Command not found)


[root@tspweb01 test]# wh
-bash: wh:Command not found
[root@tspweb01 test]# echo $?
127
[root@tspweb01 test]#

Output string to file

Outputs the specified character string to a file.

command


echo "String" >file name

Command execution example

Execution example


[root@tspweb01 test]# echo "testtest" > test.txt
[root@tspweb01 test]# cat test.txt
testtest
[root@tspweb01 test]#

Add character string to file

Adds the specified character string to the file.

command


echo "String" >>file name

Command execution example

[root@tspweb01 test]# cat test.txt
testtest
[root@tspweb01 test]# echo "testtest" >> test.txt
[root@tspweb01 test]#
[root@tspweb01 test]# cat test.txt
testtest
testtest
[root@tspweb01 test]#

Note

Please be careful not to confuse > with >> during actual work. (The meaning is completely different.)

--> : Overwrite the entire file -->> : Add one sentence to the last line of the file

Be sure to use the cp command to make a backup when working on important files.

Summary

You can do this with the echo command.

--Display of character string on the screen --Display of command execution result --Output the string to a file --Add character string to file

How about applying it to a bash script?

reference

Detailed summary of echo commands [Linux command collection] Unexpectedly convenient command true / false

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