#!/bin/bash

function F2 {
  echo "stdout A"
  # echo toto >>/tmp/toto
  # $nope
  grep titi toto
  # exit 6
  >&2 echo "This is stderr"
  echo "stdout B"
  echo "stdout C"
  # command_not_found
}

function F1 {
  echo F1
  F2
}

echo start of useless
F1
echo end of useless