Most modern text editors won't pass through every control character. Vim lets me type the unit separator, but not the record separator, for instance.

Vim has bindings for some control key combos, which is why you can't type them directly. I can type control-_ without issue, but to get an ASCII 30 (RS) to show up, I have to type control-v first (just like when at the shell prompt).

Useful hint: if you look at the output of man ascii (at least on linux with man-pages-3.22) find the control character you want to type in the left column and look in the same row on in the right column to find the letter/key to use with the control key.

For example, to type NAK, it's <control-u>. Vertical tab is <control-k>:

   $ echo <control-v><control-k> | od -c
   0000000  \v  \n

Similarly, Ctrl-L clears the screen in most Unix apps because that generates the "form feed" character, and on a line printer or paper-based teletype terminal, "form feed" means to advance to the next page -- a nice empty clear piece of paper.

This is slightly different than being able to actually generate those characters as input. If you put a control-d in a file, nothing will stop reading the file when it sees the control-d, it's just another byte. readline knows how to interpret a bunch of control characters. There's also the terminal driver that has interpretations, which you can see with `stty -a`. When the tty layer sees a control-d or a control-c, it closes stdin or generates SIGINT, respectively. But even this can be dependent on if you're on a pty or attached directly to a serial line. There's nothing special about the mapping of control-d to end-of-transmission character, that's just how the layer that sees it is interpreting it. You can, for example, change how control-c is interpreted by `stty intr ^B`, which will make control-b generate SIGINT. And there's a way to put the terminal driver in complete transparent/passthru mode.

There are more details in "man 3 termios", but be warned, the TTY layer is not a pleasant subject for reading.

I'm pretty sure every possible combination of 7-bits is assigned SOME name in ascii, and Ctrl-any-case-insensitive-letter is a defined 7bit value.

This chart says control-s is `DC3 (Device Control, X-OFF)` and control-q is `DC1 (Device Control, X-ON)`. Yup, that's what they do alright.

http://www.unix-manuals.com/refs/misc/ascii-table.html

Don't forget everyone's favorite control-G, BEL, useful sending beeps across the wire on old school IRC, BBSen, and chat services. Or, you know, telegraph machines or something.

On most Unix terminals, these have the effect of pausing and resuming the display when a bunch of data is scrolling by.

Also, the classic control-G is still in C. "\a" is "alert (beep)."

[1] http://www.asciitable.com/

And this is in fact how they show up in vim (or at least my fairly uncustomized vim), using ^ to stand for ctrl as was once conventional: `^_` and `^^`

The legacy MARC binary format still used for library data uses ascii 29, 30, and 31 -- although for reasons with probably some bizarre historical definition uses them DIFFERENTLY than defined in ascii.

0x1D == 29 == ascii group seperator == MARC Record separator

0x1E == 30 == ascii record seperator == MARC Field Terminator

0x1F == 31 == ascii unit separator == MARC subfield seperator

http://en.wikipedia.org/wiki/MARC_standards

¹You can release Control and Shift after typing "U", in which case the character will appear after you type a space. Or, you can hold Control and Shift while typing the code point, in which case the character will appear after you release either modifier key.

[1] http://www.fileformat.info/tip/microsoft/enter_unicode.htm

At least, that worked for me. Interesting that the unit separator does not have the same requirement to precede it with Ctrl-V.

More info in the vim docs:

http://vimdoc.sourceforge.net/htmldoc/insert.html#ins-specia...

You can also use Ctrl-K to enter RFC1345 digraphs, in which case unit separator is 'Ctrl-K US' and record separator is 'Ctrl-K RS'. (See :h Ctrl-K).

Emacs has similar features, as well as a nifty TeX input mode: http://stackoverflow.com/q/6269618