! syntax example in bash

Let's have this command:

$ head /etc/passwd /etc/crontab /etc/services
# more output

Repeat latest command:

$ !!
head /etc/passwd /etc/crontab /etc/services

Use latest command as parameters for other command:

$ echo !!
echo head /etc/passwd /etc/crontab /etc/services 
head /etc/passwd /etc/crontab /etc/services

Use 2nd parameter from previous command in another command. Count starts from 0:

$ vi !:2
vi /etc/crontab

Use first argument from the previous command:

$ vi !^
vi /etc/passwd

Use last argument from the previous command:

$ vi !$
vi /etc/services

Repeat the nth command from your history.
It counts from the top:

$ !10

Repeat the nth command from bottom of your history.
Counts from the bottom:

$ !-10

Repeat the last command matching a string’s beginning.
The bang (!) followed by the first character (or string) matching the command you want to run will repeat the most recent instance of that command:

$ !ma
mail

Repeat the last command matching anywhere in a string.
The !?<string> format does the same as the above, but <string> doesn’t have to be at the beginning of the command

$ !?links
vi ../links.txt

Repeat but substitute a string.
String substitution allows to rerun the commands with the new values. Here is an example:

$ head /etc/passwd
# head output
$ !!:s^passwd^crontab
head /etc/crontab

So, it will replace passwd with crontab.
You can even do the same with !<string>:s^<old>^<new>:

$ !he:s^passwd^crontab
head /etc/crontab

Print out commands.
Sometimes you might want to print out the command, but don’t want it executed. You can accomplish this task with !:p:

$ !!:p
head /etc/crontab
$ head /etc/crontab
# command output
$ !h:p
head /etc/crontab