how to force subshell on level 2 be in own pgid?

Question

Command below prints pid of subshell and subshell of subshell:

$ ( ( echo $BASHPID )& echo $BASHPID )& sleep 1
[1] 9885
9885
9887
[1]+  Done                    ( ( echo $BASHPID ) & echo $BASHPID )

Now command below is more complicated, but it indicates that second subshell is in 'process group' of first subshell:

$ ( ( echo $$ $BASH_SUBSHELL $BASHPID ; export BBB=$BASHPID; ps -e -o pid,pgid,ppid,comm | grep -E "$$|$BBB|PGID" | grep -E "bash|PGID" )& echo $$ $BASH_SUBSHELL $BASHPID; sleep 1 )& sleep 1
[3] 9973
2787 1 9973
2787 2 9975
  PID  PGID  PPID COMMAND
 2787  2787  2769 bash
 9973  9973  2787 bash
 9975  9973  9973 bash

Is there simple way to create similar command which will show unique number for last row in second column?

Answer 1

There's no way to do that since you are detaching the subshells from the current process (PGID) with the & operator therefore will run on a separate process (new PGID).

Check this ones also: How to set process group of a shell script