Common special symbols in Ubuntu

 

(>) Redirection output symbol

Usage: Command> file name

Feature: overwrite (when the input and output files are the same file, the file content is cleared; not suitable for continuous redirection)

Typical applications:

~ $ Cat a B> c (merge files)

~ $ Echo "hello world"> hello.txt (input content to the specified file)

~ $./Test. sh>/dev/null (delete program input)

(>>) Output redirection

Usage: Command> file name

Feature: append

Typical applications:

~ $ Cat hello.txt> hello2.txt

~ $./Test. sh> test. echo

(2>) Error redirection

Usage: Command 2> file name

Feature: Overwrite

Typical applications:

~ $./Test. sh> test. error

(2>) Error redirection output symbol

Usage: Command 2> file name

Feature: append error messages

Typical applications:

~ $./Test. sh 2> test. error

(|) MPs queue symbol

Usage: command 1 | command 2

Feature: the previous command output serves as the input of the next command.

Typical applications:

~ $ Ps-ef | grep root

(*) Match any character

(? ) Match any character

(&) Run commands in the background (Daemon)

Usage: command 1 &

Feature: Close the current terminal window and the program is still running

Typical applications:

~ $./Test. sh &

(&) Connect multiple commands

Usage: command 1 & command 2

Feature: If command 1 is successfully executed, continue to execute command 2; otherwise, do not execute command 2.

Typical applications:

~ $ Apt-get update & apt-get dist-upgrade

(|) Logical or

Usage: command 1 | command 2

Feature: If command 1 is successfully executed, command 2 is not executed; otherwise, command 2 is executed.

(!) Non-logical

Feature: exclude a specified range.

([X-y]) specified range

(#) Comment

("") Double quotation marks

Feature: The content contained in it is a common character, except ''\ $.

('') Single quotes

Feature: Use the content contained in it as a common character without exception.

('') Inverted quotation marks

Feature: Execute the content it contains

(\) Escape characters

Usage; \ symbol

Feature: remove the specific meaning of a symbol to make it a common punctuation.

($) Variable call symbol

Usage: $ variable

Feature: call a variable to obtain the value of the Variable

(;) Command Separator

Usage: command 1; command 2

Feature: execute commands sequentially in one line of statements.

() Overall execution

({}) Variable Separation

 

From mr_yqs