Re-execute command line with !

Bash history expansion allows you to quickly re-run previous commands using ! and the number of the command in your history.

You can adjust the size of the history by setting the HISTSIZE variable in the shell e.g. export HISTSIZE=1000. You can clear the current history with history -c.

Method

Bash keeps a history of all commands executed in the shell and this can be referenced using the ! command. Typing two !'s at the prompt will execute the previous command:

$ echo "HELLO"
HELLO
$ !!
echo "HELLO"
HELLO

The history of the bash shell can be accessed by entering history

501  echo "HELLO"
502  echo "HELLO"
503  history

Notice that each entry has an associated number which can be used to refer to the command.

Entering ! followed by a line number from the history will run that command

$ !501
echo "HELLO"
HELLO

You can also search the history by using a search string to match the command instead of a number

$ !echo
echo "HELLO"
HELLO