RE: [OT] What is DEL for?

From: Marco Cimarosti (
Date: Wed Feb 21 2001 - 13:07:40 EST

Thanks for all the public and private replies.

Now I have a much clearer understanding of the reasons behind controls 0x7F
and 0x08 (DELETE and BACKSPACE). First of all, their names now makes more
sense to me: 0x08 originally moved the writing head BACK one SPACE, while
0x7F DELETEd a column on punched paper, by cutting all the available bits.

This also casts some light on the fact that some fonts (notably JIS fonts)
have a big black box glyphs at position 0x7F: it is probably for overwriting
a character already printed on paper, so that it cannot be read anymore.

But a few people also raised some "contemporary" issues, which is what I was
trying to obtain with my question:

Doug Ewell wrote:
> You have probably already tested this, but in Windows [...]
> it simply displays as a box [...]
> Actually, I wasn't expecting this. I tested a file
> containing the text
> "ABC*DEF" (where * = DEL) and expected that at least one
> process would
> display "ABDEF" where the DEL character had deleted the C.

Did you expect this behavior because this is what you saw happening Unix or
other systems? Which systems and which applications?

BTW, thanks also for suggesting ANSI.sys: I will try and see how it behaves.

John Cowan wrote:
> In general it has none. Some systems interpret it (erroneously) as
> either "cancel previous character" (usually BS) or "interrupt process"
> (usually ^C).

Which systems interpret 0x7F as "interrupt process"? I know that this would
be 0x03 in DOS (^C), and 0x03, 0x04 or 0x1A in Unix (^C, ^D, and ^Z,
respectively), but I know nothing about other systems, e.g. Macintosh.

Valery E Ushakov (Uwe) wrote:
> On DEC (and, I belive other) terminals the <-- "Rubout" key (PC
> keyboards has "BackSpace" key in this position) generates DEL. So
> emacs, The One True Editor :-), uses ^H key (i.e. backspace) for help
> - which causes a lot of confusion for new users who have PC keyboards
> that generate backspace (^H) for <-- key.

This leads me to some more questions:

1) What happens if emacs loads Doug Ewell's text file (I.e. a text file
containing "ABC<del>DEF") and then saves it? Would the file's content be
changed to "ABDEF"?

2) Could emacs be invoked with a text file as the keyboard input? I mean a
thing like:
        emacs < mycmd.txt

3) If 2 above is possible, what would happen if mycmd.txt contains
"ABC<del>DEF<^X><^W>mytxt.txt<newline>"? Would mytxt.txt contain "ABDEF"?
(Note: I understand that ^X+^W+filename is the command to save a new file in
emacs; sorry if this is wrong)

I am not quite sure whether I made myself understood. Sorry in advance for
my clumsy way of asking things. :-)

_ Marco

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