I discovered that one can add a notification after a command you've already
started running has ended on a UNIX system by suspending the command
using “Ctrl + Z” and then typing something like
“fg ; n --msg 'Command finished'” (where “n” is the command I use for
notifications). “fg” brings a job to the foreground, and for more information
about it see
entry and the Unix Background Jobs entry on thegeekstuff.com.