Use command as notification?

[scytho]

I use the command beep and its options (-l, -f, -D, …) as a notification for new e-mails (yeah, my machine has a speaker, and I haven’t blacklisted the kernel module for it, in fact I had to unblacklist it, just because some people think it’s useless and annoying). Would be great to be able to use something like that in Signal, too.