➜  erratic losetup sdb.img
➜  erratic losetup -f sdb.img
➜  erratic ls /dev/loop0
/dev/loop0
➜  erratic losetup -a
/dev/loop0: [0018]:17523657 (/home/erratic/sdb.img)
➜  erratic sudo parted /dev/loop0
GNU Parted 3.2
Using /dev/loop0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Model: Loopback device (loopback)
Disk /dev/loop0: 8036MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system  Name                  Flags
 1      1049kB  8035MB  8034MB  fat32        Basic data partition  msftdata

(parted)