Better Bash history

By default, the Bash shell keeps the history of your most recent session in the .bash_history file, and the commands you’ve issued in your current session are also available with a history call. These defaults are useful for keeping track of what you’ve been up to in the shell on any given machine, but with disks much larger and faster than they were when Bash was designed, a little tweaking in your .bashrc file can record history more permanently, consistently, and usefully.

Append history instead of rewriting it

You should start by setting the histappend option, which will mean that when you close a session, your history will be appended to the .bash_history file rather than overwriting what’s in there.

shopt -s histappend

Allow a larger history file

The default maximum number of commands saved into the .bash_history file is a rather meager 500. If you want to keep history further back than a few weeks or so, you may as well bump this up by explicitly setting $HISTSIZE to a much larger number in your .bashrc. We can do the same thing with the $HISTFILESIZE variable.

HISTFILESIZE=1000000
HISTSIZE=1000000

The man page for Bash says that HISTFILESIZE can be unset to stop truncation entirely, but unfortunately this doesn’t work in .bashrc files due to the order in which variables are set; it’s therefore more straightforward to simply set it to a very large number.

If you’re on a machine with resource constraints, it might be a good idea to occasionally archive old .bash_history files to speed up login and reduce memory footprint.

Don’t store specific lines

You can prevent commands that start with a space from going into history by setting $HISTCONTROL to ignorespace. You can also ignore duplicate commands, for example repeated du calls to watch a file grow, by adding ignoredups. There’s a shorthand to set both in ignoreboth.

HISTCONTROL=ignoreboth

You might also want to remove the use of certain commands from your history, whether for privacy or readability reasons. This can be done with the $HISTIGNORE variable. It’s common to use this to exclude ls calls, job control builtins like bg and fg, and calls to history itself:

HISTIGNORE='ls:bg:fg:history'

Record timestamps

If you set $HISTTIMEFORMAT to something useful, Bash will record the timestamp of each command in its history. In this variable you can specify the format in which you want this timestamp displayed when viewed with history. I find the full date and time to be useful, because it can be sorted easily and works well with tools like cut and awk.

HISTTIMEFORMAT='%F %T '

Use one command per line

To make your .bash_history file a little easier to parse, you can force commands that you entered on more than one line to be adjusted to fit on only one with the cmdhist option:

shopt -s cmdhist

Store history immediately

By default, Bash only records a session to the .bash_history file on disk when the session terminates. This means that if you crash or your session terminates improperly, you lose the history up to that point. You can fix this by recording each line of history as you issue it, through the $PROMPT_COMMAND variable:

PROMPT_COMMAND='history -a'

19 thoughts on “Better Bash history

  1. Hi, thanks a lot for these useful tips, I already knew some but not all. Could tell me what was the other way to update the file .bashrc, in addition to “source. bashrc”, I can’t remember! Congratulations for the website, is fantastic.

    PS: and how to run commands without the predetermined alias?

    • I’m glad it was helpful. You can run .sh files within your environment with just a period:

      $ . .bashrc
      

      One way of bypassing aliases is to escape the first letter of your command, e.g. if you have ls aliased, you could type:

      $ \ls
      
  2. I like to have “.bash_history” in various project directories. Much like how git searches for the “.git” directory, I have an alias called “to” which does what “cd” does, but in addition, writes out the history for the old directory, changes HISTFILE, clears history, then locates and reads in the histfile for the new directory.

    When working on multiple unrelated projects simultaneously, and switching between them, it becomes much easier to find the commands you want.

  3. For me the most important use of the history file is just to look up commands I have used sometime before and now have forgotten the syntax to or the options given to it. I see the option to prevent addition of duplicates to the history file but is there also a way that the same command(s) applied to different files also do not get stored? I am assuming that the ignore-duplicate option will fail since the filenames of the files the command is operating on are different.

    • There’s probably not a built-in way to do this, but you could always use post-processing in a PROMPTCOMMAND or .bash_logout file to filter the text with awk to remove such duplicates.

  4. HISTTIMEFORMAT=’%F %T ‘ does not store the timestamps – they are stored in the histfile automatically, this just formats them in some human readable format – (per default its set to ”, so no time is displayed at all)

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