Using history in command line

The shell maintains an active command line history. It is an amazing and helpful feature that keeps the track of all the commands that have been entered. Apart from keeping track of all the commands ever typed in in the terminal, we could also reuse those commands withouth retyping them from scratch (and risking typos!).

We can utilize the command line history feature by simply writing – you’ve guessed it – history.

Additionally, we could also access our command history by checking the .bash_history hidden file found in our home directory.

$ less .bash_history
...
ls
clear
~
ls
clear
cat .bash_history
clear
cat .bash_history
less .bash_history
clear

So why is the command line history useful? As mentioned it is a powerful resource for finding and reusing past commands, and it makes the command line workflow a lot more bearable.

The history command

The file itself is not that useful because it doesn’t provide us with mechanisms to analyze the contents in more detail. But the terminal command history is here to the rescue!

$ history
7055  ls
7056  clear
7057  ~
7058  ls
7059  clear
7060  cat .bash_history
7061  clear
7062  cat .bash_history
7063  less .bash_history
7064  clear

Look at the index on the left side – more than seven thousand commands! How can we possibly search for a command that we want to re-type? For that, we can combine the history command and the grep command. Let’s say I always forget how to run my Python files with a debugger when I want to debug my Python scripts. IThe only thing I remember is the keyword pudb which is a flag that targets the debugger itself.

$ history | grep pudb
7047  python -m pudb index.py zen.txt
7049  python -m pudb index.py zen.txt

And look at that! The number on the left, as you’ve might guessed it is the line number of the command in the command line history. We can rerun this command by using history expansion that will expand a certain index into the command itself.

$ !7049                                                                       
$ python -m pudb index.py zen.txt

The exclamation point combined with history expansion serves more uses, and here are some of them:

Instead of writing !! for the last entered command, we could also press the arrow key up. We can look through the list of entered commands by using the arrow keys, and we can execute them by pressing Enter on our keyboard.

With !string and !?string we can search for a past command, although this wouldn’t be advisable due to the complexity of the history list.

History Commands

Now we will see some of the most common keystrokes used for history navigation. I already mentioned the arrow keys, and the way we can search through the history using grep, but there is an additional way of looking through the history.

Final Words

Hope you learned something interesting regarding the history mechanism in bash, please check some more Linux articles by clicking down below.

• Find in Linux with examples
• Grep use cases with examples
• Let us talk about cd (change directory)
• Bash logical operators
• Matching regex in bash
• Using test in Linux scripts
• What are Linux shell scripts?
• Using history in command line
• How to escape characters in the command line?
• The echo command in Linux