bash: notify when long running command has finished

notify_long_running.bash

DURATION_FOR_NOTIFY=10
PROMPT_ID=$RANDOM
preexec () {
  date +%s > /tmp/.time${PROMPT_ID}
  echo $1 > /tmp/.cmd${PROMPT_ID}
}
postexec() {
  OLD_TS=$(cat /tmp/.time${PROMPT_ID})
  if [[ OLD_TS -eq "" ]]; then
    return
  fi
  echo "" > /tmp/.time${PROMPT_ID}
  NEW_TS=$(date +%s)
  DURATION=`expr $NEW_TS - $OLD_TS`
  if [[ ${DURATION} -ge ${DURATION_FOR_NOTIFY} ]]; then
    CMD_NAME=$(cat /tmp/.cmd${PROMPT_ID})
    notify-send "Command '${CMD_NAME}' has finished'"
  fi
}
preexec_invoke_exec() {
  [ -n "$COMP_LINE" ] && return
  [ "$BASH_COMMAND" = "$PROMPT_COMMAND" ] && return
  preexec $(HISTTIMEFORMAT= history 2 | cut -d\  -f 4-)
}
PROMPT_COMMAND="postexec"
trap 'preexec_invoke_exec' DEBUG

I suggest an improvement and also respect other peoples PROMPT_COMMAND configurations and do the following:

PROMPT_COMMAND="postexec;$PROMPT_COMMAND"