Kill first command as soon as second exits

Question

I've been looking for best practice for this scenario for a long time.

If I have process2 that depends on process1 running beforehand. I set up an alias like:

alias both='process1 & process2'

Then, when process2 exits, I would like for process1 to exit as well (my current solution is to go back to the terminal and kill %%).

For example (to connect to an iOS device from mac over usb):

alias usbssh='/usr/local/bin/iproxy 2222 22 & ssh -p 2222 root@localhost'

How do I keep iproxy running, and kill it as soon as ssh exits?

Answer 1

Just append kill $! to the end: process1 & process2; kill $!

$! is a variable (confusingly known as a "parameter" in Bash), and will expand to the last background PID anywhere:

Expands to the process ID of the job most recently placed into the background, whether executed as an asynchronous command or using the bg builtin (see JOB CONTROL below).

%% is special, and will only expand to the last background PID in the context of shell built-in commands like fg and kill. Unfortunately this isn't clear from the man page:

The symbols %% and %+ refer to the shell's notion of the current job, which is the last job stopped while it was in the foreground or started in the background.

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PS: If you need to make this a command string, make sure kill $! is single-quoted so it's expanded at runtime. Even better, write a function instead of an alias to avoid their limitations.