Summary of the unknown usage of "!" in Linux

Preface

In fact, the humble "!" has many amazing uses in Linux that will amaze you. This article will detail the magical uses of "!". Let’s take a look at the detailed introduction.

Execute the previous command

For example, after executing the previous command, you can use the following method to execute the previous command again:

$ whereis bash #Execute command bash: /bin/bash /etc/bash.bashrc /usr/share/man/man1/bash.1.gz
$ !! # Execute the previous command again where is bash
bash: /bin/bash /etc/bash.bashrc /usr/share/man/man1/bash.1.gz

!! represents the last executed command. As you can see, when two exclamation marks are entered, it displays the previous command and executes it at the same time. Of course, we usually think of using the "UP" key to accomplish this task. But if it is based on the previous command expansion, !! will be more convenient.
For example, you want to view a file, but forget to enter more:

$ /opt/user/test.txt #Forgot to enter more
$ more !! #Isn’t this much faster?

Use it!! Isn’t it much more convenient?

Execute a command using the first or last argument of the previous command

Use the last parameter of the previous command

For example, if you use ls to list the contents of a directory without any parameters, but want to execute it again with the -al parameter without having to enter a long parameter, you can use the following method:

$ ls /proc/1/task/1/net/tcp
/proc/1/task/1/net/tc
$ ls -al !$
ls -al /proc/1/task/1/net/tcp
-r--r--r-- 1 root root 0 12月22 17:30 /proc/1/task/1/net/tcp

Here !$ represents the last parameter of the previous command.

Use the first parameter of the previous command

To use the first parameter of the previous command, just use !^, for example:

$ ls -al !^

Remove the last parameter and execute the previous command

If you want to execute the previous command without the last parameter:

$ ls -al dir #Assume dir is a very long string $ !:-
ls -al

In what scenarios might it be used? For example, if the last parameter of your previous command is a long string, and you don’t want to use it, and the backspace key is slow to delete, you can use the above method.

Use all parameters of the previous command

We mentioned earlier that we use the last parameter of the previous command. What if it is not the last parameter? It's very simple, just use !*. For example, if we make a mistake in entering the find command and want to correct it:

$ fin -name "test.zip" #The find word here is wrong.
$ find !*
find ./ -name "test.zip"
./workspaces/shell/find/test.zip
./workspaces/shell/test.zip

Use the parameters specified in the previous command

Some readers may ask, what if I only want to use one of the parameters? Just follow the rule of ![command name]:[parameter number]. For example:

$ cp -rf dira dirb/ #Copy dira to dirb
$ ls -l !cp:2 #View the contents of dira ls -l dira
total 0
-rw-rw-r-- 1 hyb hyb 0 Dec 22 17:45 testfile

The effect is more obvious when the parameters of the previous command are very long and you need to use a parameter in the middle.

Execute commands in history

We all know that we can use the history command to view previously executed commands, but how do we execute the commands in history again? We can use the "UP" key to view, but when the history command is very long, it is not very convenient. At this time, "!" comes in handy:

$ history
(More content omitted here)
2043 touch ./dira/testfile
 2044 cp -rf dira dirb/
 2045 ls -al dira
 2046 ls -l dira
 2047 ls -al dira
 2048 ls -l dira
 2049 ls -al dira
 2050 ls -l dira
 2051 history

We can see that the history command can show the previously executed commands, and we can also see a value in front of it. If we want to execute the previous cp -rf dira dirb/ command, we can actually do it in the following way:

$ !2044 #2044 is the nth command executed cp -rf dira dirb/

That is, historical commands are executed through ![historical command value].

Of course, if we want to execute the second to last command, there is a way:

$ !-2 #The exclamation mark is followed by a negative number, and the negative number represents the last number of the item

Execute historical commands by keyword

!You can execute commands based on keywords.

Execute the previous command starting with the keyword

For example, execute the previous find command:

$ !find #Execute the previous command starting with find

Execute the previous command containing the keyword

For another example, execute the previous command containing name:

$ find ./ -name "test"
./test
./find/test
$ !?name?
find ./ -name "test"
./test
./find/test

Replace the parameters of the previous command

For example:

$ find ./ -name "old*" -a -name "*.zip"

If we need to replace old with new in this command:

$ !!:gs/old/new

The role of logical negation

This is its most familiar function, for example, to delete all files except those ending with cfg:

rm !(*.cfg) # Be careful when deleting

I will not go into details here.

Summarize

The effect of the exclamation mark "!" is indeed amazing sometimes. It may have just been mentioned before! Combined with other characters to represent a certain use of a specific meaning, in fact, we can combine or expand to discover more wonderful uses. This will not be elaborated here. What other good discoveries have you made? Welcome to leave a message!

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