/etc/grub.d/30_os-prober

Grub Config show grub bootloader on shift else hide

adjust_timeout () {
        cat <<EOF
        if keystatus --shift; then
          set timeout=-1
        else
          set timeout=0
        fi
EOF
}

Grub Config: show grub bootloader on shift else hide

adjust_timeout () {
  if [ "x${found_other_os}" = "x" ] ; then
    if [ "x${GRUB_HIDDEN_TIMEOUT}" != "x" ] ; then
      if [ "x${GRUB_HIDDEN_TIMEOUT_QUIET}" = "xtrue" ] ; then
    verbose=
      else
    verbose=" --verbose"
      fi

      if [ "x${GRUB_HIDDEN_TIMEOUT}" = "x0" ] ; then
    cat <<EOF
if [ \${timeout} != -1 ]; then
  if keystatus; then
    if keystatus --shift; then
      set timeout=-1
    else
      set timeout=0
    fi
  else
    if sleep$verbose --interruptible 3 ; then
      set timeout=0
    fi
  fi
fi
EOF
      else
    cat << EOF
if [ \${timeout} != -1 ]; then
  if sleep$verbose --interruptible ${GRUB_HIDDEN_TIMEOUT} ; then
    set timeout=0
  fi
fi
EOF
      fi
    fi
  fi
}