Re: [dev] Backspace (was: st stutter and freeze ...)

From: Christoph Lohmann <>
Date: Thu, 10 Apr 2014 17:03:55 +0200


On Thu, 10 Apr 2014 17:03:55 +0200 "Roberto E. Vargas Caballero" <> wrote:
> No answer? Anyone have anything to say? It is a big change, and
> if nobody say anything then I will change it.

Don't top post.

> > Well, I am going to comment why I want to change the behaviour of
> > this key. When ascii was defined in 1968 communication with computers
> > were done using punched cards, or hardcopy terminals (basically a
> > typewritter machine connected with the computer using a serial
> > port). Due to this, ascii defines DELETE as 7F, because in the
> > puched cards, it means all the holes of the card punched, so it is
> > a kind of 'phisical delete'. In the same way, BACKSPACE key was a
> > non destructive back space, as in typewriter machines. So, if you
> > wanted to delete a character, you had to BACKSPACE and then DELETE.
> > Other use of BACKSPACE was accented characters, for example 'a
> > BACKSPACE `'. The VT100 had no BACKSPACE key, it was generated
> > using the CONTROL key as another control character (CONTROL key sets
> > to 0 b7 b6 b5, so it converts H (code 0x48) into BACKSPACE (code
> > 0x08)), but it had a DELETE key in a similar position where BACKSPACE
> > key is located today in common PC keyboards. All the terminal
> > emulators emulated correctly the difference between these keys, and
> > backspace key generated a BACKSPACE (^H) and delete key generated
> > a DELETE (^?).
> >
> > But the problem arised when Linus Torvald wrote Linux, and he did
> > that the virtual terminal (the terminal emulator integrated in the
> > kernel) returns a DELETE when backspace was pressed, due to the
> > fact of the key in that position in VT100 was a delete key. This
> > created a lot of problems (you can see it in [1] and [2]), and how
> > Linux became the king, a lot of terminal emulators today generate
> > a DELETE when backspace key is pressed in order to avoid problems
> > with linux. It causes that the only way of generating a BACKSPACE
> > in these systems is using CONTROL + H. I also think that emacs had
> > an important point here because CONTROL + H prefix is used in emacs
> > in some commands (help commands).
> >
> > >From point of view of the kernel, you can change the key for deleting
> > a previous character with stty erase. When you connect a real terminal
> > into a machine you describe the type of terminal, so getty configure
> > the correct value of stty erase for this terminal, but in the case of
> > terminal emulators you don't have any getty that can set the correct
> > value of stty erase, so you always get the default value. So it means
> > that in case of changing the value of the backspace keyboard, you have
> > to add a 'stty erase ^H' into your profile. Of course, other solution
> > can be that st itself modify the value of stty erase.
> >
> > I have usually the inverse problem, when I connect with non Unix machines,
> > and I have to press control + h to get a BACKSPACE, or the inverse,
> > when a user connects to my unix machines from a different system with
> > a correct backspace key.
> >
> > I would like listen the opinion of st users about this topic before
> > of doing this kind of modifications.

I don’t have any case which interferes with this. So apply it.


Christoph Lohmann
Received on Thu Apr 10 2014 - 17:03:55 CEST

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