The Yancy CMS for the Mojolicious web framework currently supports three different database systems directly (and even more through the DBIx::Class ORM). As a result, when doing development, I need to have two database daemons running locally, a bunch of different environment variables to tell the tests where those databases are, and a web daemon to test the front-end.

Setting up these daemons is a pain, but I also do not want to run them all the time (to save on my laptop's battery). To me, it's easier to run a database daemon for a specific project than to try to manage all the databases I might need. But that means that every time I want to do some work on Yancy, I need to start up a bunch of things.

Since I do all my development in a terminal window, the Tmux terminal multiplexer has become an extremely useful tool. Using a shell script and Tmux, I can run a single command to set up all the databases, environment variables, and all the tabs I need to get to work quickly.

Tmux allows me to set up multiple "windows" in a single terminal, kind of like tabs in a browser. Each window can then be split into panes horizontally and vertically. Each pane has a program running inside, usually a shell (like bash) that I can run commands in (like vim, my editor). I can do all this by typing commands in the tmux session: Ctrl+B C to create a new window, Ctrl+B % to split the current pane vertically, Ctrl+B " to split the current pane horizontally, etc...

But, I can also interact with Tmux via the tmux command. Everything I can do by typing in the Tmux session I can do with the tmux command: tmux new-window creates a new window, tmux split-pane -v splits a pane vertically, tmux split-pane -h splits a pane horizontally. By using these commands, I can set up a complex set of windows and panes in Tmux inside a shell script:

tmux new-session -s yancy -d
tmux new-window -t yancy:2
tmux send-keys -t yancy:1 vim Enter
tmux send-keys -t yancy:2.0 "export TEST_YANCY_EXAMPLES=1" Enter

First, I create a new Tmux session named "yancy" and create a new window. Then I run vim, my editor, in the first window, and set up an environment variable in the second window. Next I need to run my databases. I create a new window to run Postgres in one pane, and then split that pane to run MySQL in the other pane.

tmux new-window -t yancy:3 postgres -D ~/perl/Yancy/db/pg
tmux split-window -t yancy:3 mysqld --skip-grant-tables --datadir ~/perl/Yancy/db/mysql

Finally, I need to attach to my session. But also, if my session is already running, I don't want to initialize it again. So, I wrap the entire thing in a shell conditional.

if ! tmux has-session -t yancy; then
    tmux new-session -s yancy -d
    # ... Initialize the session
fi
tmux attach -t yancy

Now with one command I'm ready to develop! This script is available in the Yancy repository for anyone to use. Tmux makes working on Yancy easy!