Create bootable Windows installer (virtual) drive image from Linux

mkwinimg.sh

#!/bin/bash
die(){
 echo -e "\n$1"
 echo -e "\nUsage: $0 /path/to/windows.iso /path/to/output.img [gpt|mbr]\n"
 exit
}
[ "$(id -u)" != "0" ] && die "You must be root to run this script"
[ -f "$1" ] && iso="$1" || die "Error: $1 does not exist"
[ ! -f "$2" ] && img="$2" || die "Error: $2 already exists"
[[ ${3,,} = "mbr" ]] && { mode=1; echo "Mode: MBR"; } || { mode=0; echo "Mode: GPT"; }
curl -LJO https://github.com/pbatard/rufus/raw/master/res/uefi/uefi-ntfs.img
fallocate -l 6GiB "$img"
parted "$img" -s mklabel `[ $mode = 1 ] && echo msdos || echo gpt`
loop=`losetup --partscan --show --find "$img"`
bs=`lsblk -bno log-sec "$loop" |head -1`
size=$(((`stat -c '%s' uefi-ntfs.img`+$bs-1)/$bs))
parted "$img" -s mkpart primary ntfs 4MiB -- -`[ $mode = 1 ] && echo $(($size+1)) || echo $(($size+1+33))`s
parted "$img" -a none -s mkpart primary fat16 -- -`[ $mode = 1 ] && echo $size || echo $(($size+33))`s -`[ $mode = 1 ] && echo 1 || echo $((1+33))`s
losetup -d "$loop"
loop=`losetup --partscan --show --find "$img"`
mkntfs -Q -I -L "Windows_USB" "${loop}p1"
mkdir /tmp/iso /tmp/img
mount --options loop,ro --types udf,iso9660 "$iso" /tmp/iso
mount "${loop}p1" /tmp/img
rsync -Pr /tmp/iso/ /tmp/img
if [ $mode = 1 ]
then
 grub-install --target=i386-pc --boot-directory=/tmp/img --force "$loop"
 echo -e "ntldr /bootmgr\nboot" > /tmp/img/grub/grub.cfg
fi
umount /tmp/iso /tmp/img
rm -rf /tmp/iso /tmp/img
dd if=uefi-ntfs.img of="${loop}p2"
losetup -d "$loop"
# convert image file for use with virtualbox
vboxmanage convertfromraw --format vdi --variant fixed "$img" "$img.vdi"
unset -v iso img mode bs size loop

Script to create drive image file for Windows installer - specifymbr or gpt to partition accordingly.