Shell script to archive & encrypt folders

snapshot.sh

#!/usr/bin/env zsh
#
# Snapshot archive of all contents in the folder defined in a variable
# called $SOURCE, using $TAR_OPTS tar options.
#
# Created MM, 2012-01-21
# Revised MM, 2023-11-03
set -eu

source ${COMMON_UTILS}/utils
BASEDIR=$(abspath $(dirname $0))

function usage {
  printf "Usage: %s [-n | -h] DEST SOURCES\n\n" $(basename "$0")
  cat << EOF
Snapshot archive of all contents in the SOURCE folder, using \$TAR_OPTS tar options.

If the -n flag is specified, it will abort if the destination file (or its
encrypted version) are already present.

Requires a virtualenv called 'crytto' with this package installed (pip install crytto)

Options:
  -n     Non-interactive mode. Abort if the destination file already exists.
  -h     Prints this help and exits

Arguments:
  SOURCES   Required. The source folders to archive and encrypt.
  DEST      Required. Destination path for the encrypted archive: omit any
            file extension, .tar.gz.enc will be automatically appended
EOF

}

function check_mount {
  local tag="$1"
  if [[ ! -e "$tag" ]]; then
    msg "Attempting to mount destination folder ${DEST}"
    mount $DEST
    if [[ ! -e "$tag" ]]; then
      fatal "No tag file [${tag}] on ${DEST}, aborting"
    fi
  fi
}

function validate {
  local file_extension_regex='^.+\.[^.]+$'

  if [[ ! -x $(which filecrypt) ]]; then
    fatal "Missing filecrypt executable in virtualenv ${VENV}"
  fi
  if [[ -z ${SOURCES} ]]; then
    fatal "At least one SOURCE folder must be specified"
  fi
  if [[ ${DEST} =~ ${file_extension_regex} ]]
  then
    usage
    fatal "DEST should have no extension"
  fi
  if [[ -e ${DEST}.tar.gz.enc ]]; then
    if [[ ${ASK} == "n" ]]; then
      fatal "Encrypted archive $(basename ${DEST}) already exists, aborting"
    fi
    read -p "File ${DEST}.tar.gz.enc already exists, overwrite? [y/N] " overwrite
    if [[ $overwrite != 'y' ]]; then
      fatal "Snapshot canceled"
    fi
  fi
}

declare ASK="y"
while getopts ":hn" opt; do
  case ${opt} in
    h)
      usage
      exit 0
      ;;
    n)
      ASK="n"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      usage
      exit 1
      ;;
  esac
done
shift $((OPTIND -1))

if [[ ${ASK} == "n" ]]; then
  msg "Non-Interactive option given (-n)"
fi

if [[ $# < 2 ]]
then
  usage
  fatal "Not enough arguments"
fi

declare -r DEST="${1:-}"
shift 1
declare -r SOURCES=$@
declare -r TMP_DIR=$(mktemp -d)
declare -r TAG="$(dirname ${DEST})/tag"
declare -r TARBALL="${TMP_DIR}/$(basename ${DEST}).tar.gz"
declare -r VENV="crytto"

# Activates Virtualenv with the `crytto` module installed
source ${WORKON_HOME}/${VENV}/bin/activate

validate
check_mount $TAG

msg "Archiving files in ${SOURCES}: creating snapshot in ${DEST}"
msg "Creating temporary plaintext tarball in ${TARBALL}"

if [[ ! -f ${TARBALL} ]]
then
  # We deactivate exit-on-error, as tar will throw some errors
  # which are safe to ignore.
  set +e
  # We use J (xz compression) instead of z (gzip), as apparently
  # it should provide better compression.
  sudo tar caJf "${TARBALL}" ${TAR_OPTS} ${SOURCES}
  set -e
else
  msg "${TARBALL} exists, skipping archive"
fi

if [[ ! -f "${TARBALL}" ]]
then
  fatal "Failed to create snapshot"
fi
sudo chown ${USER}:users "${TARBALL}"

msg "Encrypting ${TARBALL} to ${TARBALL}.enc"
filecrypt -o ${TARBALL}.enc ${TARBALL}

msg "Moving ${TARBALL}.enc to ${DEST}"
mv "${TARBALL}.enc" "${DEST}.tar.gz.enc"

success "Created snapshot archive $(ls ${DEST}*)"