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Wow, didn't really expect you to read this far down. The latest iteration of the site is in open beta. It's a gentle open beta-- not in prime-time just yet. It's being hosted over at UpGuard (link) and you are more than welcome to give it a shot. Couple things:
Allows system to be halted and session closed by KDE. Very useful to save applications states, especially with the KDE apps that behave correctly.
Referring to the original post, if you are using $! then that means the process is a child of the current shell, so you can just use `wait $!`. If you are trying to wait for a process created outside of the current shell, then the loop on `kill -0 $PID` is good; although, you can't get the exit status of the process.
If you really _must_ use a loop, this is better than parsing the output of 'ps':
PID=$! ;while kill -0 $PID &>/dev/null; do sleep 1; done
kill -0 $PID returns 0 if the process still exists; otherwise 1
The '[r]' is to avoid grep from grepping itself. (interchange 'r' by the appropriate letter)
Here is an example that I use a lot (as root or halt will not work):
while (ps -ef | grep [w]get); do sleep 10; done; sleep 60; halt
I add the 'sleep 60' command just in case something went wrong; so that I have time to cancel.
Very useful if you are going to bed while downloading something and do not want your computer running all night.