overlay-changes

#!/bin/bash

if (( $(id -u) != 0 )); then
  echo "This script must be run as root"
  exit 127
fi

opt_exit_status=0
write_diff="overlay.diff"

while [ "$1" ]; do
  case $1 in
    --no-diff)
      write_diff=""
      ;;
    --diff)
      write_diff="$2"
      shift 1
      ;;
    --no-*)
      var="${1##--no-}"
      var="opt_${var//-/_}"
      if [[ ${!var} ]]; then
        eval "$var=0"
      fi
      ;;
    --*)
      var="${1##--}"
      var="opt_${var//-/_}"
      if [[ ${!var} ]]; then
        eval "$var=1"
      fi
      ;;
    --|*)
      break
      ;;
  esac
  shift 1
done

if temp="$( mktemp --directory /tmp/overlay-runner-XXX )"; then
  trap "rm -rf $temp" EXIT

  mkdir "$temp/overlay"
  mkdir "$temp/root"
  mkdir "$temp/work"

  mount -t overlayfs -o rw,lowerdir=/,upperdir="$temp/overlay",workdir="$temp/work" overlayfs "$temp/root"
  chroot "$temp/root" "${@}"
  exit_code="$?"
  umount "${temp}/root"

  DIFF="$(diff -ru "/" "${temp}/overlay" | grep -v ^Only)"
  if [[ $write_diff ]]; then
    echo "$DIFF" > "$write_diff"
  fi
  if (( $opt_exit_status )); then
    exit $exit_code
  elif [[ "$DIFF" == "" ]]; then
    exit 0
  else
    exit 1
  fi
else
  exit 126
fi