Scripting tmux

tmux ranks highly on the list of programs that I cannot live without. I consider its split-screen and terminal multiplexing capabilities absolutely essential for day-to-day hacking. It belongs to that rare breed of software that has measurably improved my development productivity, software that makes me genuinely happy.

This is what my tmux pane layout usually looks like when I’m working on a project:

 ---------------------------------------------------------------
|                               |                               |
|                               |                               |
|                               |                               |
|                               |             repl              |
|                               |                               |
|       directory operations    |                               |
|       git interactions        |-------------------------------|
|       etc.                    |                               |
|                               |        directory watcher      |
|                               |        server                 |
|                               |        logger                 |
|                               |        etc.                   |
|                               |                               |
 ---------------------------------------------------------------

Since I use this layout for nearly every project that I work on, it makes sense to have tmux automatically set it up for me so that I don’t have to type a bunch of keyboard shortcuts every time I start working on a new project. Luckily, tmux is highly scriptable. Here’s a BASH function that automatically sets up the three-pane layout from above:

setup_tmux_layout() {
    # Create a new window.
    tmux new-window -a -n "$1" -c "$2"

    # Now split it twice, first horizontally and then vertically.
    tmux split-window -h
    tmux split-window -v
}

Now I can run the following from my shell:

$ setup_tmux_layout <window_name> <starting directory>

(Note that at least one tmux session must be active for this to work. This function affects the most recently active tmux session.)

This is good, but we can go a step further. I have several Django projects, and whenever I start working on one of them there are a number of additional Python/Django-specific actions that I take.

• Switch to the project directory in all three panes.
• Activate the project’s virtualenv in all three panes.
• Run a git status in the large pane on the left.
• Start a Django shell (python manage.py shell) in the top right pane.
• Run the Django development server (python manage.py runserver) in the bottom right pane.

Once again, it makes sense to automate these actions. Here is the actual code I have in my ~/.bash_profile to do that.

workon_project() {
    if [ $# -lt 2 ]
        then
            echo "Usage:"
            echo -e "tworkon_project <project directory> <virtualenv name>"
            return 1
    fi

    # Create a new window.
    tmux new-window -a -n "$2" -c "$1"

    # Send keys to the large pane on the left.
    tmux send-keys "workon $2" C-m
    tmux send-keys "git status" C-m

    # Split the window horizontally.
    tmux split-window -h -c "$1"

    # Send keys to the top right pane.
    tmux send-keys "workon $2" C-m
    tmux send-keys "python manage.py shell" C-m

    # Split the window again, this time vertically.
    tmux split-window -v -c "$1"

    # Send keys to the bottom right pane.
    tmux send-keys "workon $2" C-m
    tmux send-keys "python manage.py runserver" C-m
}

Brilliant! Now I can perform all those tedious actions in one fell swoop by running this in my shell:

$ workon_project <project directory> <virtualenv name>

(In case you are wondering, the workon command above comes from virtualenvwrapper.)

This little function has saved me hundreds of keystrokes in the last few months, and it only scratches the surface of what tmux is capable of. If you are a regular tmux user, I highly recommend skimming the tmux manpage at least once.