trapping signal from "docker stop" in bash

Since Docker 1.9, you can use the STOPSIGNAL instruction in your Dockerfile:

STOPSIGNAL signal

The STOPSIGNAL sets the system call signal that will be sent to the container to exit. This signal can be a valid unsigned number that matches a position in the kernel’s syscall table, for instance 9, or a signal name in the format SIGNAME, for instance SIGKILL.

Source: https://docs.docker.com/engine/reference/builder/#stopsignal

Have a look at this, could be inspiring :-)

UPDATE:

@nick-humrich here it is is my lamer copy & past (credit goes to the original author https://github.com/lgierth )

#!/bin/bash

function ensure_started_container {
  exists=`docker ps -q | grep $1`
  if [ "$?" = "0" ] ; then
    echo "[docker-exec] skipping docker start, already started"
  else
    output=`docker start "$1"`
    echo "[docker start] $output"
  fi
  running=1
}

function setup_signals {
  cid="$1"; shift
  handler="$1"; shift
  for sig; do
    trap "$handler '$cid' '$sig'" "$sig"
  done
}

function handle_signal {
  echo "[docker-exec] received $2"
  case "$2" in
    SIGINT)
      output=`docker stop -t 5 "$1"`
      echo "[docker stop] $output"
      running=0
      ;;
    SIGTERM)
      output=`docker stop -t 5 "$1"`
      echo "[docker stop] $output"
      running=0
      ;;
    SIGHUP)
      output=`docker restart -t 5 "$1"`
      echo "[docker restart] $output"

      # restart logging
      docker attach "$1" &
      kill "$logger_pid" 2> /dev/null
      logger_pid="$!"
      ;;
  esac
}

running=0

setup_signals "$1" "handle_signal" SIGINT SIGTERM SIGHUP

ensure_started_container "$1"

docker attach "$1" &
logger_pid="$!"

while true; do
  if [ "$running" = "1" ]; then
    sleep 1
  else
    break
  fi
done

exit_code=`docker wait "$1"`
exit "$exit_code"

Old question, but this will do the trick:

#!/bin/bash

echo starting up

exec /opt/myapp

For details take a look here: https://akomljen.com/stopping-docker-containers-gracefully/