The necessary operation for those big guys to fly 666 inadvertently at the bash command line terminal

shell Command line operations

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brief introduction

Bash Built in Readline library , This library provides many “ Line operation ” function , For example, automatic completion of commands , It can greatly speed up the operation .

This library defaults to Emacs Shortcut key , It can also be changed to Vi Shortcut key .

$ set -o vi

The following command can be changed back to Emacs Shortcut key .

$ set -o emacs

If you want to permanently change the editing mode （Emacs / Vi）, You can write the command in ~/.inputrc file , This file is Readline Configuration file for .

set editing-mode vi

The shortcuts described in this chapter belong to Emacs Pattern .Vi Mode shortcut key , Readers can refer to Vi Editor tutorial .

Bash This library is enabled by default , But closing is allowed .

$ bash --noediting

In the above command ,--noediting Parameter closed Readline library , Starting up Bash There is no line operation function .

2. Cursor movement

Readline Provides shortcut keys for quickly moving the cursor .

• Ctrl + a： Moved to the beginning of a line .
• Ctrl + b： Move a character to the beginning of the line , Same as the left arrow .
• Ctrl + e： Moved to the end of each line .
• Ctrl + f： Move a character to the end of the line , Same as the right arrow .
• Alt + f： Move to the end of the current word .
• Alt + b： Move to the beginning of the current word .

The shortcut keys above Alt key , It can also be used. ESC Key instead of .

3. Clear the screen

Ctrl + l The shortcut key can clear the screen , Moves the current line to the first line of the screen , And clear Orders work the same .

4. Edit operation

The following shortcut keys can edit the contents of the command line .

• Ctrl + d： Delete character at cursor position （delete）.
• Ctrl + w： Delete the word in front of the cursor .
• Ctrl + t： The character at the cursor position is exchanged with the character in front of it （transpose）.
• Alt + t： The word at the cursor position is exchanged with the word in front of it （transpose）.
• Alt + l： Change the cursor position to lowercase at the end of the word （lowercase）.
• Alt + u： Change the cursor position to uppercase at the end of the word （uppercase）.

[!NOTE|style:flat|lable:Mylable|iconVisibility:hidden]
Use Ctrl + d When , If there are no characters in the current line , Will lead to exit from the current Shell, So be careful .

The shortcut keys for cutting and pasting are as follows .

• Ctrl + k： Cut the text from the cursor position to the end of the line .
• Ctrl + u： Cut the text where the cursor is positioned to the beginning of the line .
• Alt + d： Cut the text from the cursor position to the end of the word .
• Alt + Backspace： Cut the text from the cursor position to the beginning of the word .
• Ctrl + y： Paste text at the cursor position .

similarly ,Alt Key can be used Esc Key instead of .

5. Automatic completion

Halfway through the command , You can press Tab key ,Readline Will automatically complete the command or path . such as , Input cle, Then press the Tab key ,Bash This command will be automatically completed as clear.

If there are more than one qualified command or path , You need to press it twice in a row Tab key ,Bash All qualified commands or paths will be prompted .

Except for commands or paths ,Tab You can also complete other values . If a value with $ start , Press Tab The key will complete the variable ; If the ~ start , Then complete the user name ; If the @ start , Then complete the host name （hostname）, Host names are listed in /etc/hosts The host in the document shall prevail .

The shortcut keys related to automatic completion are as follows .

• Tab： Complete auto completion .
• Alt + ?： List possible completions , And double click Tab Same bond action .
• Alt + /： Try file path completion .
• Ctrl + x /： According to the first Ctrl + x, Press again /, Equate to Alt + ?, List possible file paths to complete .
• Alt + !： Command Completion .
• Ctrl + x !： According to the first Ctrl + x, Press again !, Equate to Alt + !, Command Completion .
• Alt + ~： Complete the user name .
• Ctrl + x ~： According to the first Ctrl + x, Press again ~, Equate to Alt + ~, Complete the user name .
• Alt + $： Variable name completion .
• Ctrl + x $： According to the first Ctrl + x, Press again $, Equate to Alt + $, Variable name completion .
• Alt + @： Complete the host name .
• Ctrl + x @： According to the first Ctrl + x, Press again @, Equate to Alt + @, Complete the host name .
• Alt + *： Insert all possible completions at once on the command line .
• Alt + Tab： Try to use .bash_history It used to execute commands , To complete .

above Alt Keys can also be used ESC Key instead of .

6. Operation history

6.1 Basic usage

Bash The user's operation history will be preserved , That is, every command entered by the user will be recorded . With the operation history , You can use the arrow keys ↑ and ↓, Quickly browse the previous and next command .

Quit current Shell When ,Bash Will put the user in the current Shell Write the operation history of ~/.bash_history file , The file is stored by default 500 Operations .

environment variable HISTFILE Always point to this file .

$ echo $HISTFILE
/home/me/.bash_history

history The command will output the entire contents of this file . The user can see all the recently executed commands , Each command is preceded by a line number . The closer the command , Behind the other side .

$ history
...
498 echo Goodbye
499 ls ~
500 cd

When entering a command , Press down Ctrl + r Shortcut key , You can search the operation history , Select a previously executed command . At this point, type the beginning of the command ,Shell It will be automatically in the history file , Query and display the last matching result , Then press enter , Will execute that order .

The following method can quickly execute the previously executed commands .

$ echo Hello World
Hello World

$ echo Goodbye
Goodbye

$ !e
echo Goodbye
Goodbye

In the example above ,!e To find out the history of operations , The latest one is e The first command and execute .Bash Which command will be output first echo Goodbye, And then directly execute .

Empathy ,!echo We will also implement the latest one to echo The first order .

$ !echo
echo Goodbye
Goodbye

$ !echo H
echo Goodbye H
Goodbye H

$ !echo H G
echo Goodbye H G
Goodbye H G

Be careful ,!string Syntax only matches commands , It doesn't match the parameters . therefore !echo H Not execute echo Hello World, It's about executing echo Goodbye, And put the parameters H Attached to this order . Empathy ,!echo H G It's also equivalent to echo Goodbye Add... After the command H G.

because !string The syntax will be expanded to include previously executed commands , So it contains ! String in double quotation marks , You have to be very careful , If it is followed by a non space character , It is very likely to report an error .

$ echo "I say:\"hello!\""
bash: !\: event not found

The above command will report an error , The reason is that there is a backslash after the exclamation point ,Bash Will try to find , Have you ever executed a command that begins with a backslash before , If it is not found, an error will be reported . The solution is to precede the exclamation point , Plus a backslash .

$ echo "I say:\"hello\!\""
I say:"hello\!"

6.2 history command

As I said before ,history The command can display the operation history , namely .bash_history The content of the document .

$ history

Use this command , Instead of reading directly .bash_history The advantage of the document is , It will precede all operations with line numbers , The most recent operation is at the end , Maximum line number .

By customizing the environment variables HISTTIMEFORMAT, The time of each operation can be displayed .

$ export HISTTIMEFORMAT='%F %T '
$ history
1  2013-06-09 10:40:12   cat /etc/issue
2  2013-06-09 10:40:12   clear

In the above code ,%F amount to %Y - %m - %d,%T amount to %H : %M : %S.

Just set HISTTIMEFORMAT This environment variable , Will be in .bash_history The execution time stamp of the File Save command . If not set , The timestamp will not be saved .

environment variable HISTSIZE Set the number of save history operations .

$ export HISTSIZE=10000

The above command settings are saved in the past 10000 Operation history .

If you don't want to save the history of this operation , You can set HISTSIZE be equal to 0.

export HISTSIZE=0

If HISTSIZE=0 Write to the user's home directory ~/.bashrc file , Then the user's operation history will not be preserved . If written /etc/profile, The whole system will not retain operation history .

environment variable HISTIGNORE You can set which commands are not written to the operation history .

export HISTIGNORE='pwd:ls:exit'

The above example sets ,pwd、ls、exit These three commands do not write operation history .

If you want to search for a previously executed command , Can cooperate with grep Command search operation history .

$ history | grep /usr/bin

The above command returns .bash_history In the document , Those contain /usr/bin The order of .

Each record of the operation history has a number . After knowing the command number , You can use exclamation marks + Number to execute the command . If you want to execute .bash_history The inside number 8 Bar command , You can do this as follows .

$ !8

history Ordered -c Parameter can clear the operation history .

$ history -c

7. Related shortcuts

Here are some shortcut keys related to operation history .

• Ctrl + p： Displays the last command , Same effect as the up arrow （previous）.
• Ctrl + n： Show the next command , Same effect as the down arrow （next）.
• Alt + <： Display the first command .
• Alt + >： Show the last command , The current command .
• Ctrl + o： Execute the current entry in the history file , And automatically display the next command . This is useful for repeating a sequence of commands .

Exclamatory mark ! The shortcut keys are as follows .

• !!： Execute the last order .
• !n：n Is the number , The line number in the execution history file is n The order of .
• !-n： Before executing the current command n A command of .
• !string： Execute the latest to specify the string string The first order .
• !?string： Execute the last containing string string The order of .
• !$： Represents the last parameter of the previous command .
• !*： Represents all parameters of the previous command , That is, all parts except the command .
• ^string1^string2： Execute the latest entry that contains string1 The order of , Replace it with string2.

Here is !$ and !* Example .

$ cp a.txt b.txt
$ echo !$
b.txt

$ cp a.txt b.txt
$ echo !*
a.txt b.txt

In the above example ,!$ Represents the last parameter of the previous command （b.txt）,!* Represents all parameters of the previous command （a.txt b.txt）.

Here is ^string1^string2 Example .

$ rm /var/log/httpd/error.log
$ ^error^access
rm /var/log/httpd/access.log

In the above example ,^error^access Put the latest one containing error In the order of error, Replace with access.

If you want to determine what the command is , And then execute , Can open histverify Options . In this case , Use ! Commands generated by shortcut keys , It will print out first , Wait until the user presses the Enter key .

$ shopt -s histverify

Other shortcuts

• Ctrl + j： Equivalent to enter （LINEFEED）.
• Ctrl + m： Equivalent to enter （CARRIAGE RETURN）.
• Ctrl + o： Equivalent to enter , And show the next command in the operation history .
• Ctrl + v： Change the next special character to a literal , For example, carriage return becomes ^M.
• Ctrl + [： Equate to ESC.
• Alt + .： Insert the last word of the previous command .
• Alt + _： Equate to Alt + ..

above Alt + . Shortcut key , For very long file paths , Sometimes it's very convenient . because Unix The last argument to the command is usually the file path .

$ mkdir foo_bar
$ cd # Press down  Alt + .

In the example above , stay cd Press... After the command Alt + ., Will be automatically inserted foo_bar.

Reference resources ：

• Bash Line operation