# Get next free loop device
dev=$(sudo losetup)
# Setup loop device, scan for partitions to appear in /dev
sudo losetup -P -f $file
devs=$(
sudo fdisk $dev <<-EOF | awk '/\/dev\/loop/ { print $1 }'
p
q
EOF
)
for dev in $devs
do
p=${dev##*p}
sudo mkdir /mnt/$p
sudo mount $dev /mnt/$p
# ...
sudo umount /mnt/$p
done
sudo losetup -d $dev