Time and again, you come across plain-text files with invalid ASCII
characters, possibly as a result of pasting from non-ASCII documents -
for instance PDF files.

As a result, your shell script may rot, your Latex compilation might
break, your C code might fly off the handle, ...

When you need to be sure your text file is 100% good, pure ASCII, you
need chkascii - a small C utility that checks for invalid characters.

chkascii treats valid ASCII values in a text file as the austere set:

{ 32-126 / 9 (horizontal tab) / 10 (line feed a.k.a. Unix newline) }

Anything else is considered junk, although the user can pass in
additional ASCII values to treat as good.

chkascii additionally checks whether the file is EOL-terminated.
If the file  is  neither  empty  nor terminated with ASCII 10, chkascii
treats the condition as an error too (albeit of a different kind).