count-forks() {
	local prev_pid=$(echo $BASHPID)
	"$@"
	local next_pid=$(echo $BASHPID)
	echo "$* -> $(( next_pid - prev_pid - 1 )) fork(s)"
}

func1() {
	echo hello | cat -n
}

func2() {
	cat -n <<< hello
}

func3() {
	echo hello
}

count-forks func1
count-forks func2
count-forks func3