What is bang dollar (!$) in Bash?
Bang dollar seems to refer to the last part of the last command line.
Eg
$ ls -l
.... something
$ !$
-l
bash: -l command not found
I can find plenty on the dollar variables (eg $! ) but not on this. Any explanation?
That's the last argument of the previous command. From the documentation:
!!:$
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, eg, with aliases.
!$ 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
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