BASH - Check if PID Exists

Question

I want to stall the execution of my BASH script until a process is closed (I have the PID stored in a variable). I\'m thinking

while [PID IS RUNNING]; do
sleep 5         


        

Answer 1

kill -s 0 $pid will return success if $pid is running, failure otherwise, without actually sending a signal to the process, so you can use that in your if statement directly.

wait $pid will wait on that process, replacing your whole loop.

Answer 2

It seems like you want

wait $pid

which will return when $pid finishes.

Otherwise you can use

ps -p $pid

to check if the process is still alive (this is more effective than kill -0 $pid because it will work even if you don't own the pid).

Answer 3

I always use the following tail -f /dev/null --pid $PID. It doesn't require explicit loop and isn't limited to your shell's children pids only.

Answer 4

ps --pid $pid &>/dev/null

returns 0 if it exists, 1 otherwise

Answer 5

You might look for the presence of /proc/YOUR_PID directory.