Command History

Ever had that moment where you think, "I swear I just typed that exact command five minutes ago"? Well, the shell's got your back.

If you've ever knocked up a super long command or just want a quick redo of something you've done, the shell has some nice tricks up its sleeve. Enter the shell history – it's like your diary, logging all those commands you've entered. Want to see? Just throw in the history command if you're using bash. From there, you've got the power to pull up those old commands, tweak them, or just run them again.

Stick aroundfor the next bit, where we'll dive into the magic of command-line editing; finishing off half-typed command lines, and navigating through your command history.

Customise History ENV Variables

The way the history command operates is steered by three environment variables:

• HISTCONTROL

• HISTIGNORE

• HISTTIMEFORMAT

HISTCONTROL

The HISTCONTROL variable defines whether or not to remove any duplicate commands from your history, or commands that begin with spaces, or both!

By default, both are removed

You may find it more useful to only omit duplicates:

export HISTCONTROL=ignoredups

HISTIGNORE

The HISTIGNORE variable is particularly useful for filtering out basic commands that are run frequently, such as ls, exit, history, bg, etc:

export HISTIGNORE="&:ls:[bf]g:exit:history"

mkdir test

cd test

~/test# ls

~/test# pwd
/home/kali/test

~/test# ls

~/test# history
1 export HISTIGNORE="&:ls:[bf]g:exit:history"
2 mkdir test
3 cd test
4 pwd

As you can see, the ls command is missing form history.

HISTTIMEFORMAT

Lastly, HISTTIMEFORMAT controls date and/or time stamps in the output of the history command:

history
1 2018-02-12 13:37:33 export HISTIGNORE="&:ls:[bf]g:exit:history"
2 2018-02-12 13:37:38 mkdir test
3 2018-02-12 13:37:40 cd test
4 2018-02-12 13:37:43 pwd
5 2018-02-12 13:37:51 export HISTTIMEFORMAT='%F %T '

In this example, we used %F (Year-Month-Day ISO 8601 format) and %T (24-hour time). Other formats can be found in the strftime man page.