Bash: receive messages from background process

Question

I'm sending data via cansend to vcan0, at the same time I'm listening to messages that has been send to vcan0 via candump vcan0.

For some reason, i won't receive any messages, when sending data to vcan0 through the script, but when i send data through terminal, the script receives data, somehow.

cansend vcan0 004#0152FEE400000000 # sending data to vcan0
while true;
do
  msg_candump=$(candump vcan0) # read vcan0
  if [[ ${#msg_candump} > 1 ]]; then #received msg
    echo $msg_candump
  fi
done

Answer 1

this did the job:

while true;
do
  cansend vcan0 '004#0152FEE400000000'
  sleep 1
  msg_candump="$(candump vcan0 -n 1)" # read vcan0
  if [[ ${#msg_candump} > 1 ]]; then #received msg
    echo $msg_candump
    msg_candump=${msg_candump// /} # leerzeichen entfernen
    msg_candump=${msg_candump:19:8} # substring holen
    msg_candump=${msg_candump,,} #lowercase
    if [[ $msg_candump != `git log -1 --format="%h"`0 ]]; then
      echo "git pull"
      #git pull
      break
    fi
  fi
  sleep 0.025
done