Bash – How to run multiple commands together in the background

You can use the command wait PID to wait for a process to end.

You can also retrieve the PID of the last command with $!

In your case, something like this would work:

command1 & #run command1 in background
PID=$! #catch the last PID, here from command1
command2 #run command2 while command1 is running in background
wait $PID #wait for command1, in background, to end
command3 #execute once command1 ended

Following your edit, as you have multiple PIDs and you know them, you can do that:

command1 & #run command1 in background
PID1=xxxxx
PID2=yyyyy
PID3=xxyyy
PID4=yyxxx
command2 #run command2 while command1 is running in background
wait $PID1 $PID2 $PID3 $PID4 #wait for the four processes of command1, in background, to end
command3 #execute once command1 ended

If you don't want the background to apply to the whole line, then use eval:

sleep 2 && eval 'sleep 10 &'

Now only the second command will be a background job, and it will be a proper background job that you can wait on.