Launch a process on the background, then start a loop waiting for the process completion.

wait_and_see.sh

#!/bin/bash

cmd="sleep 5s"
# Run a command
nohup $cmd > /dev/null 2>&1 &
pid=$!

# Here is the process id
echo $pid

# Wait for the process to finish
while true ;
do
  ps -p $pid > /dev/null
  if [[ $? == 0 ]];
    then
      echo "Waiting..."
      sleep 2s
    else
      # Exiting
      break;
  fi
done

echo "Bye bye..."