• Posts
  • RSS
  • ◂◂RSS
  • Contact

  • You Should Be Logging Shell History

    February 13th, 2012
    shell, logging, tech  [html]
    Do you work on the command line? If so, you should be logging your shell history. Don't shells already do this? Not enough. They log only the most recent commands [1] and they don't include when or where you ran them. Not only that, but they don't save until the shell exits, which means you lose the data in a crash. It's a mess, but you can fix it: tell the shell to log this information immediately before it shows the next command prompt. [2] For bash, put this in the init file [3]:
      promptFunc() {
        # right before prompting for the next command, save the previous
        # command in a file.
        echo "$(date +%Y-%m-%d--%H-%M-%S) $(hostname) $PWD $(history 1)" \
          >> ~/.full_history
      }
      PROMPT_COMMAND=promptFunc
    
    You'd think running these extra commands would slow your system down, and I'm sure they do relative to doing nothing or having this built into the shell, but the prompt still feels like it appears instantly.

    Your shell history is an invaluable resource in understanding what you were doing earlier, and keeping a permanent log is well worth it.

    For quick history searching, add:

    function histgrep {
      local n_lines=10
      if [[ "$1" =~ ^[0-9]*$ ]]; then
        n_lines="$1"
        shift
      fi
      grep "$@" ~/.full_history | tail -n "$n_lines"
    }
    
    Usage:
    $ histgrep foo
    ... ten lines of history ...
    $ histgrep 100 foo
    ... a hundred lines of history ...
    

    (Yes, I've written about this before, but I'm continually surprised how many people don't have something like this. It saves me gobs of time.)


    [1] Bash defaults to 500 lines. At my previous job I had ~100K lines logged while at my current one I have 73K.

    [2] This does mean that if you have a crash while a command is running that command will not be written back to the history file. This is bad, but I don't think there's a 'post command entry' hook in bash.

    [3] On my Mac this goes in ~/.bash_profile; on Linux I'd put it in ~/.bashrc. For other shells you'll need something similar.

    Comment via: google plus, facebook, r/commandline

    Recent posts on blogs I like:

    Learning Worst Industry Practices

    If I have a bad idea and you have a bad idea and we exchange them, we now have two bad ideas. But more than that. If I have a bad idea and you have a good idea and we exchange them, we should both land on your good idea – but that requires both […]

    via Pedestrian Observations September 20, 2020

    Collections: Iron, How Did They Make It? Part I, Mining

    This week we are starting a four-part look at pre-modern iron and steel production. As with our series on farming, we are going to follow the train of iron production from the mine to a finished object, be that a tool, a piece of armor, a simple nail, a w…

    via A Collection of Unmitigated Pedantry September 18, 2020

    Learning Game

    I came up with this game. In the game one person thinks of something and then gives the other person a clue. And the other person writes a guess down on a blackboard or a piece of paper. Or really anything you have that's laying around that's av…

    via Lily Wise's Blog Posts September 17, 2020

    more     (via openring)


  • Posts
  • RSS
  • ◂◂RSS
  • Contact