A non-printing character is a character which won’t actually get directly printed (or displayed) but rather interpreted. Such non-printing characters are for example line-feed or tabulation. The interpretation of those characters can differ from one system to the next. For example the line-feed character is different on Unix or DOS.

If you need an easy way to confirm that a text file is DOS or UNIX formatted (they differ with respect to the end of line character(s) for example) or if you wish to display normally non-printing characters of a text file, you can use the -vET command line switches of the cat utility.

As explained in the man page :

• -v : will use the ^ and M- notation for control and multibytes characters
• -E : will make ends of lines visible
• -T : will make tabulations visible

For example :

If you downloaded an ISO file and you want to mount it into your filesystem, you can proceed as follows :
spaghetti% sudo losetup /dev/loop0 cdrom.iso<br /> spaghetti% sudo mount /dev/loop0 /mnt<br /> spaghetti% ls /mnt<br /> Autorun.inf setup.exe setup.ico<br /> spaghetti%<br /> [...]<br /> spaghetti% sudo umount /mnt<br /> spaghetti% sudo losetup -d /dev/loop0

This will use the feature known as “loop devices”, which lets you use a file as a device, and subsequently mount it as it would be one.