I'm trying to figure an easy way to generate certain control characters such as NUL and EOF from the keyboard for testing purposes.

Does anyone know how to do it?

This is possible on Windows/DOS by turning the Num Lock key on, and then holding down the ALT key while you enter the numeric code from the keypad.

I'm assuming there is a similar mechanism with Linux.

Have you tried just using the appropriate control character? (I can't think of an easy way to test this, or I would have.) For example, Ctl-@ is NUL, Ctrl-\ is FS, etc.

Also note that you can send such characters to STDOUT (or redirect or pipe them) using echo:

echo -en "\nnn"

will send the character whose octal value is nnn, i.e.

echo -en "\033"

sends an escape.

BTW, I don't think there is an ASCII character designated EOF, although IIRC, MS-DOS used Ctl-Z for this purpose on text files.

EDIT: I just found out how to test just using the Ctrl key and it does indeed work except for the characters the shell wants to interpret such as Ctrl-C.

Thanks for the tips blackhole. I was able to do most of what I wanted by just using VI/VIM to edit text files. Apparently from insert mode, you can do ctrl-v, followed by ctrl-? to insert a control character within a text file. The only one that did not quite work for me was the EOF character, which would have truncated my file.