Linux - Working with the history of your last fired actions

For me, one of the undeniable strengths of the command line under Linux is the management of the history of previously executed commands.

To be able to press the Up or Down keys on the keyboard to return to previously run commands, wow.

For older users, there was DOSKEY under MSDos, but Linux goes much further.

Let's look at a few tricks.

Getting your history

First things first, to display the list of commands you've entered in the past, simply start history in a Linux console.

Location of your history

By default, your history is stored in a file called .bash_history in your home directory. You can display the last five commands f.i. by running tail -n5 ~/.bash_history.

On my own, since I'm using ZSH, my history is in ~/.zsh_history.

The easiest way to determine where is stored your history is to show the content of the $HISTFILE variable like this: echo $HISTFILE.

tip

Very recently, I had to take over a script developed by a colleague (let's call him JohnDoe) and I didn't know how to call it from the command line or what parameters to pass to it.

As I'm a root user on the server, I simply consulted his history. All I had to do was display its /home/john_doe/.bash_history file.

HISTIGNORE // HISTORY_IGNORE variables

The HISTIGNORE (for Bash) or the HISTORY_IGNORE (ZSH) variable can be used to specify some patterns you don't want to be saved in your history file.

Let's take an example: HISTIGNORE="sudo *" will prevent all commands starting with sudo to be written in the history file.

You can also use a pattern like HISTIGNORE="*password*" to prevent commands having the word password to be written.

To be able to specify more than one rule, just use the pipe | character like in HISTIGNORE="sudo * | *password*".

Don't put a specific command in the history

Imagine a command like curl --user name:password http://www.example.com. Did you really want to put that command (so your login and password in plain text) in the history file?

Using ZSH, I just need to add a space before my command so by running [SPACE]curl --user name:password http://www.example.com.

# So, don't start your command like this:
$ curl --user name:password http://www.example.com

# v--- But just add a space character before
$  curl --user name:password http://www.example.com

info

The space character is triggered by the hist_ignore_space option, defined in .oh-my-zsh/lib/history.zsh.

Using grep to filter your history

Let's say you wish to retrieve the latest docker exec instructions you've fired: history | grep -i "docker exec" i.e. simply pipe the output of the history command to the grep one and apply a filter (case insensitive using the -i flag).

On my own, I don't need this because I'm using CTRL+R under ZSH.

CTRL-R is your friend

The CTRL+R keystrokes will display a small popup window (both in Bash or ZSH) and you'll be able to quickly search in your command’s history.

Below the look&feel for ZSH; much better and easier than under Bash.

So press CTRL+R then start to type some letters like gacom and every entry having these letters (like git add . ; git commit ... will be retrieved).

Autosuggestions in the console using ZSH

By using ZSH and zsh-autosuggestion (see my previous post) you even don't need anymore to care about the history.

Just start to type the first letters of a command like doc and all your previous docker fired statements will be accessible (just use navigation keys to select a previous command or type some more letters to be more restrictive).

Delete an instruction from your history

Ouch! You've forgotten to add a single space before your confidential instruction so, now, it's stored in the history.

No panic! The history file is ... a file so just run vi $HISTFILE and you can edit it.

Or, perhaps easier, just use history -d followed by the line number as displayed in the history output.

So if the output of history is the one below, I can remove the vi line by running history -d 2130

2129  history | grep -i "docker exec"
2130  vi $HISTFILE
2131  history | grep -i "docker exec"

tip

But, then the command history -d 2130 will appears in the history, of course. So editing the file using a text editor is perhaps more ... discreet.

note

You can specify a range like history -N 2100-2130.