commit f210ea26c444607980d5de17ed7d4e62bb813631 (patch)
parent 8306568bd0b9d082c58ad897b4562ffe6822e585
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date: Thu, 24 Jul 2014 19:56:58 +0200
Add info about Backspace and Delete to the FAQ
Diffstat:
| M | FAQ | | | 58 | ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
1 file changed, 58 insertions(+), 0 deletions(-)
diff --git a/FAQ b/FAQ
@@ -98,3 +98,61 @@ If you want to compile st for OpenBSD you have to remove -lrt from config.mk, an
st will compile without any loss of functionality, because all the functions are
included in libc on this platform.
+## Backspace key does not work
+
+This is an issue that was discussed in suckless mailing list
+<http://lists.suckless.org/dev/1404/20697.html>:
+
+ 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.
+
+ [1] http://www.ibb.net/~anne/keyboard.html
+ [2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html
+
