Here’s a few tricks that I often use on the command line to save time. They take advantage of some variables that the bash shell uses to store various aspects of your history.
Repeating the last command with !!
Sometimes I run a command that requires sudo access, but forget the sudo. This is a great opportunity to use !! which holds the last command you ran.
$ tail /var/log/mail.log
tail: cannot open `/var/log/mail.log' for reading: Permission denied
$ sudo !!
sudo tail /var/log/mail.log
# output of command
