This tiny, standalone Bash script does one simple thing: wait for the most recently started command in the tmux session to finish running.

Bash makes it easy to run commands sequentially: chain them together with ;, or even && if you're in touch with your faults. But, this chaining only works if you remember to use it before firing off that first command.

Let's say you want to shut down your machine after the full system upgrade you just hit enter on, but you forgot to add && shutdown at the end. You could either stare listfully screenward until your computer is safe to put down, or you could switch to another terminal and use this one simple trick to make sure shutdown runs after the update finishes:

waitmux && shutdown now

Waitmux finds that upgrade process and waits for it to finish before exiting, giving you another chance to use that && shutdown.

Since figuring out which command to wait for could be error-prone, this script assumes that the user always uses exactly one tmux session to run all their shells. This provides a narrower set of candidate processes to wait for, ensuring that only an explicitly-typed command is selected.

If you don't use tmux, but like this general idea, I'm sure it could be adapted to other use-cases.