This is an extension of my last BASH post, Taking Control: More BASH Tips. In that post we discussed some of the control commands that are available for clearing the screen, searching the history and moving the cursor around. This time we are going to talk about modifying the text in the current command.

CTRL+_ or CTRL+-
Let’s start out with the thing that we all need sometimes, undo. Control and underscore or dash will undo the last control command done in bash. It WILL NOT undo the last command executed on the system. For example if you cut all of the text from the cursor to the beginning of the line but really ment to cut the last word you can use undo.

#I want to change badger to fox.
j2consulting:~ user1$ The quick brown badger jumps over the lazy dog.
#I hit CTRL+u instead of CTRL+w
j2consulting:~ user1$ jumps over the lazy dog.
#CTRL+- saves me from my mistake
j2consulting:~ user1$ The quick brown badger jumps over the lazy dog.

CTRL + u, CTRL + w, CTRL + k
As I showed in the previous example, you can remove text from the current command. Using these control commands you can delete text based on the current cursor position. Control and u will delete all of the text from the point of the cursor to the beginning of the command. Control and k will delete all of the test from the point of the cursor to the end of the command. Finally, control and w will delete the previous word in the command.

#I want to change badger to fox.
j2consulting:~ user1$ The quick brown badger jumps over the lazy dog.
#I move the cursor to the space between badger and jumps and then hit CTRL+w
j2consulting:~ user1$ The quick brown jumps over the lazy dog.
#Now I can add fox.
j2consulting:~ user1$ The quick brown fox jumps over the lazy dog.
#I don't like the end so I move the cursor to the space between fox and jumps and hit CTRL+k
j2consulting:~ user1$ The quick brown fox
#And now I change the ending.
j2consulting:~ user1$ The quick brown fox hides while the dog chases him.
#But now it's just wrong and I want to delete everything from the end to the beginning so I hit CTRL+u
j2consulting:~ user1$

CTRL + y
So you have just got done cutting all kinds of text, what is the next logical thing? Paste. Any of the text you cut using the previous 3 commands can be pasted into the line. Let’s switch the sentence around to put the dog first.

j2consulting:~ user1$ The quick brown fox jumps over the lazy dog.
#Putting my cursor on the . and hitting CTRL+w I cut the previous word.
j2consulting:~ user1$ The quick brown fox jumps over the lazy .
#Now I put my cursor between fox and jumps and hit CTRL+y
j2consulting:~ user1$ The quick brown foxdog jumps over the lazy .
#Now I put my cursor on the d in dog and hit CTRL+w
j2consulting:~ user1$ The quick brown dog jumps over the lazy .
#Finally I put my cursor on the . again and hit CTRL+y to paste the fox
j2consulting:~ user1$ The quick brown dog jumps over the lazy fox.

CTRL + t
It is a fairly common mistake to transpose two characters while typing. Control and t can help us quickly fix this by swapping the previous two characters.

j2consulting:~ user1$ Teh
#Oops, I ment to spell The, hit CTRL+t
j2consulting:~ user1$ The
#This can also work if you want to move the cursor to the mistake.
j2consulting:~ user1$ Teh quick brown fox jumps over the lazy dog.
#By placing the cursor between the h and q and hitting CTRL+t we can fix the mistake.
j2consulting:~ user1$ The quick brown fox jumps over the lazy dog.

By using the tricks in this and previous BASH posts you can significantly reduce the time it takes you to get things done. If you know of any other tricks I’d love to hear about them in the comments.

Most of the work I do is on systems who’s primary interface is BASH. BASH is the shell that runs on most Linux distributions and Mac OS X when you open a terminal or SSH in. There are a few short cuts I have picked up along the way that are built into BASH but aren’t all that obvious or in the man ( manual ) pages. One very powerful shortcut, ! ( refered to as bang ), is used in BASH to reference the prior command(s) in varius ways and can really speed up your work in the terminal.

!$
The command that this post is named for is used to reference the last argument in the previous command. For example, let’s say you set up a new directory for your client you would need to set the ownership and permissions on it.

mkdir /dir/made/for/client1
chown client1:client1 /dir/made/for/client1
chmod 750 /dir/made/for/client1

This can be shortened by using the !$ shortcut like this.

mkdir /dir/made/for/client1
chown client1:client1 !$
chmod 750 !$

The time savings here are minor but over time can help, by referencing the first command we also reduce the number of typos.

!!
This command references the complete previous command. “Doesn’t the up arrow do that?” you ask? The up arrow pulls the previous command up, allowing you to run it again or modify it. !! allows you to insert the previous command into what you are typing. Take the previous example, if you didn’t have permission to make the directory the first time you tried you could try it again using sudo, like this.

mkdir /dir/made/for/client1 (returns an error about permission denied)
sudo mkdir /dir/made/for/client1 (works)

This can be shortened using the !! shortcut like this.

mkdir /dir/made/for/client1 (returns an error about permission denied)
sudo !! (works)

!number or !-number
BASH, in most configurations, keeps a history of your commands. You can see a list of those commands using the command history.

server01:~ j2$ history
26 command1
27 command2
28 command3
29 command4
30 command5
31 command6
32 command7
33 command8
34 command9
35 history

You can reference any of these commands using the number next to them and the ! shortcut. If I wanted to run command5 again I would do this.

!30

You can also reference commands in reverse by negating them. If I remembered that I ran command5 six commands ago I could do this.

!-6

!:number
By putting a : and a number after the ! you can reference individual arguments in a previous command. Each “word” in a command gets assigned a number, starting with 0. For example, in the command chmod 750 /dir/made/for/client1 chmod = 0, 750 = 1, and /dir/made/for/client1 = 2. So if I had to change the permissions on a few directories it would look like this.

chmod 750 /dir/made/for/client1
chmod 750 /dir/made/for/client2
chmod 750 /dir/made/for/client3

Using the shortcut it would look like this.

chmod 750 /dir/made/for/client1
!:0 !:1 /dir/made/for/client2
!:0 !:1 /dir/made/for/client3

Finally, the last shortcut and this one can be combined to reference specific parts of a command in your history list. Say I just did all those chmod commands above but forgot to chown client1′s dir. Using the combination I could do this.

chown client1:client1 !-3:2

You can now see why ! is one of my favorite tools while working in BASH. If you have any questions or know of another way to use !, please leave a comment.