What is bang dollar (!$) in Bash?

Question

Bang dollar seems to refer to the last part of the last command line.

E.g.

$ ls -l  .... something $ !$ -l bash: -l command not found 

I can find plenty on the dollar variables (e.g. $!) but not on this. Any explanation?

Answer 1

That's the last argument of the previous command. From the documentation:

!!:$

designates the last argument of the preceding command. This may be shortened to !$.

Remark. If you want to play around with Bash's history, I suggest you turn on the shell option histverify like so:

shopt -s histverify 

(you can also put it in your .bashrc to have it on permanently). When using history substitution, the substitution is not executed immediately; instead, it is put in readline's buffer, waiting for you to press enter… or not!

---

To make things precise, typing !$ is not equivalent to typing "$_": !$ is really a history substitution, refering to the last word of the previous command that was entered, whereas "$_" is the last argument of the previously executed command. You can compare both (I have shopt -s histverify):

$ { echo zee; } zee $ echo "$_" zee $ { echo zee; } zee $ echo !$ $ echo } 

Also:

$ if true; then echo one; else echo two; fi one $ echo "$_" one $ if true; then echo one; else echo two; fi $ echo !$ $ echo fi 

And also:

$ echo zee; echo "$_" zee zee $ echo zee2; echo !$ $ echo zee2; echo "$_" 

And also

$ echo {1..3} 1 2 3 $ echo "$_" 3 $ echo {1..3} 1 2 3 $ echo !$ $ echo {1..3} 

And also

$ echo one ; $ echo "$_" one $ echo one ; one $ echo !$ $ echo ; 

There are lots of other examples, e.g., with aliases.

Answer 2

!$ can do what $_ does, except the fact that $_ does not store the value it returns (as its substitution) to history.

Here is an example.

With !$

za:tmep za$ ls -lad  drwxr-xr-x  4 za  staff  136 Apr  6  2016 . za:tmep za$ !$ -lad -bash: -lad: command not found za:tmep za$ history | tail -n 3   660  ls -lad    661  -lad                     <<== history shows !$ substitution.     662  history | tail -n 3 

With $_

za:tmep za$ ls -lad drwxr-xr-x  4 za  staff  136 Apr  6  2016 . za:tmep za$ $_ -bash: -lad: command not found za:tmep za$ history | tail -n 3   663  ls -lad   664  $_         <<== history shows $_ and not its substitution.    665  history | tail -n 3 za:tmep za$  

More options:

!^      first argument !:2     second argument !:2-$   second to last arguments !:2*    second to last arguments !:2-    second to next to last arguments !:2-3   second to third arguments !$      last argument !*      all arguments