Use trap to Do Cleanup Work When Script Terminates

Now I have the script that monitoring the output of several UART devices:

#!/bin/bash

for i in `seq 0 7`; do
# use grep here to enforce line-buffered output, so concurrent
# input from UART isn't messed up
    cat /dev/crbif0rb0c${i}ttyS0 | grep ^ --line-buffered &
done

wait

But there is one problem, when you terminate the script (ctrl+c), these cat processes won't be killed, so that the next time you run this script, you'll not be able to access these UART device since they are busy.

To solve this problem, we need to do some cleanup work when the script terminates. In this case, we need to kill these cat processes. We can use the trap command to do this. Basically, trap enables you to register a kind of handler for different kind of signals.

In this case, we can add a line into the script:

trap "pkill -P $$" SIGINT

for i in `seq 0 7`; do
# use grep here to enforce line-buffered output, so concurrent
# input from UART isn't messed up
    cat /dev/crbif0rb0c${i}ttyS0 | grep ^ --line-buffered &
done

wait

$$ is the process id of the script. pkill -P $$ will kill all the child processes of $$. So that when the script terminates (SIGINT signal from ctrl+c), this pkill command will be executed and all the cat processes will be killed.

Thanks to these post.