Mounting LUKS filesystem like usual

mount.luks

#!/bin/bash
#
# Copyright (C) 2019 Emanuele Tomasi <targzeta@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# Mounting LUKS filesystem like usual.

# Running without arguments for the help.

function _exit {

  if type "$1" >& /dev/null
  then
    $1
  else
    echo "$1"
  fi

  (( $2 == 2 )) && echo && _usage

  exit $2
}

function _usage {
cat <<- EOL
Usage: $SCRIPT_NAME device|dir
   or: $SCRIPT_NAME device dir
   or: $SCRIPT_NAME -u dir|device
EOL
}

SCRIPT_NAME=${0##*/u}

############################
# PARSING THE COMMAND LINE #
############################
[[ $# < 1 || $# > 2 ]] && _exit _usage 1

UMOUNT=0
while getopts :u arg
do
  case $arg in
    u) UMOUNT=1
  esac
done
shift $(( $OPTIND-1 ))

[[ ${0##*/} =~ ^umount ]] && UMOUNT=1

#################
# SANITY CHECKS #
#################
[[ $(whoami) != 'root' ]] &&
  _exit 'Only root can do it!' 1

declare -a dev_dir
if (( $UMOUNT == 1 ))
then
  (( $# != 1 )) && _exit _usage 1

  dev_dir=($(grep "\s${1%/}\s" /etc/mtab | awk '{print $1 " " $2}'))
else
  if (( $# == 1 ))
  then
    dev_dir=($(grep "\s${1%/}\s" /etc/fstab | awk '{print $1 " " $2}'))
  else
    dev_dir=("$1" "$2")
  fi
fi

[ -z "${dev_dir[0]}" ] && _exit "Dir or device not found: $1" 2

[ ! -b "${dev_dir[0]}" ] && _exit "Device not found: ${dev_dir[0]}" 2
[ ! -d "${dev_dir[1]}" ] && _exit "Dir not found: ${dev_dir[1]}" 2

########
# MAIN #
########
DM_NAME=$(basename "${dev_dir[1]}")

if (( $UMOUNT == 0 ))
then
  cryptsetup open --type luks "${dev_dir[0]}" "$DM_NAME"
  ret_code=$?
  (( $ret_code == 2 )) && _exit "Wrong password?" 1
  (( $ret_code != 0 )) && exit 1
  mount /dev/mapper/"$DM_NAME" "${dev_dir[1]}"
else
  umount "${dev_dir[1]}" && cryptsetup close $DM_NAME
fi