Remove unused loop devices

free_unused_loop_dev.sh

#!/bin/sh
for LOOPS in $(losetup -a | awk -F':' {'print $1'} | awk -F'/' {'print $3'}); do
  for LOOPPART in $(ls /dev/mapper/${LOOPS}*| awk -F'/' {'print $4'}); do 
    dmsetup remove ${LOOPPART};
  done;
  losetup -d /dev/${LOOPS};
done

Seriously? You guys have an error message and there is written Try 'losetup --help' for more information. but it's too hard to look into this?

$ /sbin/losetup --help | grep detach
 -d, --detach <loopdev>...     detach one or more devices
 -D, --detach-all              detach all used devices

Indeed, the command from @captn3m0 works, but I replaces the losetup --d by losetup -d which can be easily spotted in the --help output.