Bash: Start and kill child process

Question

I have a program I want to start. Let' say this program will run a while(true)-loop (so it does not terminate. I want to write a bash script which:

1. Starts the program (./endlessloop &)
2. Waits 1 second (sleep 1)
3. Kills the program --> How?

I cannot use $! to get pid from child because server is running a lot of instances concurrently.

Answer 1

Store the PID:

./endlessloop & endlessloop_pid=$!
sleep 1
kill "$endlessloop_pid"

You can also check whether the process is still running with kill -0:

if kill -0 "$endlessloop_pid"; then
  echo "Endlessloop is still running"
fi

...and storing the content in a variable means it scales to multiple processes:

endlessloop_pids=( )                       # initialize an empty array to store PIDs
./endlessloop & endlessloop_pids+=( "$!" ) # start one in background and store its PID
./endlessloop & endlessloop_pids+=( "$!" ) # start another and store its PID also
kill "${endlessloop_pids[@]}"              # kill both endlessloop instances started above

See also BashFAQ #68, "How do I run a command, and have it abort (timeout) after N seconds?"

The ProcessManagement page on the Wooledge wiki also discusses relevant best practices.