How to type non-printable ASCII characters in Mac OS X Terminal?

Question

To communicate with a serial-type device over a telnet socket, I need to type the null character (ASCII 0) and all other non-printable ASCII characters.

On Windows, you hold ALT and type the ASCII code.

How do I do this on Mac OS X?

Answer 1

Ctrl-Space sends ASCII NUL. For the general case, System Preferences > Personal > Language and Text > Input Sources, scroll down the list and select Unicode Hex Input. You can then use Shift-Cmd-Space (and, if you disable Spotlight's use of it, Cmd-Space) to switch between input modes or assign it a keyboard shortcut of its own (and presumably another to switch back) in System Preferences > Hardware > Keyboard > Keyboard Shortcuts. Once Unicode Hex Input is enabled, you hold down Option and type the 4 digit hex code; on releasing Option it should be typed. You could stay in that mode as long as you don't need any characters beyond U+007F (or of course type them all with hex input instead of, say, Option-e e to type é).

Answer 2

In many CLI/TUI applications you can press CtrlV in order to tell the application to accept the next keypress as raw character codes instead of invoking its normal function.