cancel current execution after of a new event

[emilgpa]

I have the following script:

fswatch ts |
while read; do
    echo "changes received";

    echo "compiling typescript files..";
    tsc -p ts/; 

    echo "compiling files with babel...";
    babel ES6 -d scripts --babelrc ES6/babelconfig.json;

    echo "OK";
done

the execution inside of while take 15 seconds, I want that when a new event is raised cancel the current execution and execute it again. How can I do? I know really little about shell script...

[seaside98]

@DasHaus I created something very similar for a project I'm working on. Basically, you find the PID of the running script and kill it. You may need to change the "fswatch"...

# Find the PIDs
pids=$(ps -ef | grep "fswatch" | grep -v grep | awk '{print $2}')

# Kill them
if [ -n "$pids" ]; then
    kill -9 $pids
fi

# ...

[emilgpa]

And How I can detect when a new event is raised?. Thanks you very much!

[seaside98]

@DasHaus You will just put that at the beginning of your current script. If any fswatch's are running, they will be stopped, and then yours will be started.

[seaside98]

@DasHaus Oh, wait. I see what you mean. It will look something like:

fswatch.bash --

fswatch ts |
while read; do

    # Find the PIDs
    pids=$(ps -ef | grep -E "babel|tsc" | grep -v grep | awk '{print $2}')

    # Kill them
    if [ -n "$pids" ]; then
        kill -9 $pids
    fi

    #Start compiling
   ./compile.bash

done

compile.bash --

echo "changes received";

echo "compiling typescript files..";
tsc -p ts/; 

echo "compiling files with babel...";
babel ES6 -d scripts --babelrc ES6/babelconfig.json;

echo "OK";

[emilgpa]

thanks, then I have this in this moment:

compile(){
    p "compiling typescript files.." &&
    tsc -p ts/ &&

    p "transpiling files with babel..." &&
    babel -q ES6 -d scripts --babelrc ts/babelconfig.json &&

    p "OK";
    p "waiting for new changes...";
}

compile;

fswatch ts |
while read; do
    # Find the PIDs
    pids=$(ps -ef | grep -E "babel|tsc" | grep -v grep | awk '{print $2}')

    # Kill them
    if [ -n "$pids" ]; then
        kill -9 $pids
    fi

    p "changes received";
    compile;
done

And don't works... The problem is that the block inside of while It is not executed until the previous iteration ends...

[emilgpa]

The new event is executed when the previous event ends. I don't know if is possible read the events queue in fswatch

[emcrisostomo]

That's expected: compile will have to finish before the next while iteration is executed. Use:

compile.sh &

or

nohup compile.sh &

instead.

[emilgpa]

Aaaah, ok!. I understand now. The & is the key. Finally, I can do it in one file:

p(){
    now="$(date +'%r')"
    printf "$(tput setaf 1)%s$(tput sgr0) | $(tput bold)$1$(tput sgr0)\n" "$now";
}

compile(){
    p "compiling typescript files.." &&
    tsc -p ts/ &&

    p "transpiling files with babel..." &&
    babel -q ES6 -d scripts --babelrc ts/babelconfig.json &&

    p "OK!" &&
    p "waiting for new changes...";
}

compile &

fswatch ts |
while read; do
    p "new changes received!"

    # Find the PIDs
    pids=$(ps -ef | grep -E "babel|tsc" | grep -v grep | awk '{print $2}')

    # Kill them
    if [ -n "$pids" ]; then
        p "cancelling actual event..."; kill -9 $pids &> /dev/null
    fi

    compile &
done

It works like a charm! Thanks you both! 👍

[emcrisostomo]

You're welcome.

I suggested you using a separate script for the compilation job so that it would be easier to isolate its PID and kill it (and its child processes).

I'm glad you've found a working solution.

[AntoinePrv]

Hi,
For anyone finding this issue, I've made a minimally reproducible example that also make it easier to track the pid. Feedback is welcome :)

long_command(){
	clear
	printf "Starting"
	sleep 1
	printf "."
	sleep 1
	printf "."
	sleep 1
	printf "."
	sleep 1
	printf " done!\n"
}

cancel_and_run() {
	while read; do
		if [ ${command_pid:-0} -gt 0 ]; then
			# Loop until process is effectively killed (synchronous)
			while pkill -P $command_pid 2>/dev/null; do sleep 0.5 ; done
		fi

		( long_command ) &
		local command_pid=$!
	done
}

fswatch somefile | cancel_and_run