image.sh

#!/bin/bash
rm -f disk.img

dd if=/dev/zero of=disk.img bs=1M count=256
parted disk.img mklabel gpt
parted disk.img mkpart ESP fat32 1MiB 255MiB
parted disk.img set 1 esp on
LOOPBACK=$(losetup -o $((2048 * 512)) --sizelimit $((254 * 1024 * 1024)) -f disk.img --show)

mkfs.vfat -F 16 -n "EFI System" $LOOPBACK

mkdir img
mount $LOOPBACK img

grub-install \
  --target=x86_64-efi \
  --efi-directory=img \
  --boot-directory=img/boot \
  --removable \
  --no-nvram

cp boot/ img/ -r

umount img
rm -r img

losetup -d $LOOPBACK