both of these scripts are called using your image file as the argument

derp_close.sh

#!/bin/bash

if [ ! -f $1 ]; then
  echo no file to close
  exit 1
fi

LUFIL=$1
LODEV=$(losetup -j $LUFIL | cut -d: -f1)

MNAM="derp"

umount /media/$MNAM
cryptsetup luksClose $MNAM
losetup -d $LODEV
rmdir /media/$MNAM

echo done

derp_open.sh

#!/bin/bash

if [ ! -f $1 ]; then
  echo no file given
  exit 1
fi

modprobe dm_crypt
modprobe loop

LUFIL=$1
LODEV=$(losetup -f)
MNAM="derp"

losetup $LODEV $LUFIL

cryptsetup luksOpen $LODEV $MNAM

mkdir -p /media/$MNAM
mount /dev/mapper/$MNAM /media/$MNAM

echo done