That command would work only in Puppy, not in other distros.
As it's a script, made by our forum member SunBurnt.
You may find it in /usr/sbin.
It detects file type and mounts accordingly.
Supported filetypes : iso, sfs, 2fs/ext2, 2fs/ext3, 4fs/ext4, img, initrd/initrd.gz (Atleast in Fatdog, the script is modified by Jamesbond, so puppy version script may be slightly different)
Also works with Porteus supporting xzm modules. Handy as the mount command will loop you around forever. Anyways - posted it after using it with a script, remembered it from years ago.`