I just ran into a need to see what non-printable (non-visible?) characters were embedded in a text file in a Unix system, when I remembered this old sed command:
sed -n 'l' myfile.txt
Note that the character in that sed command is a lower-case letter "L", and not the number one ("1").
This command shows the contents of your file, and displays some of the nonprintable characters with the octal values. On some systems tab characters may also be shown as ">" characters.
This is similar to using the
cat command, except for the handling of the non-printing characters. I think you can also see something similar with the vi "binary mode" argument, like this:
vi -b myfile.txt