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author | Roberto E. Vargas Caballero <k0ga@shike2.com> | 2014-07-24 19:56:58 +0200 |
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committer | Roberto E. Vargas Caballero <k0ga@shike2.com> | 2014-07-25 17:09:27 +0200 |
commit | f210ea26c444607980d5de17ed7d4e62bb813631 (patch) | |
tree | 3eef52a8582e7a7ca9f6fce13c0722749538779f /FAQ | |
parent | 8306568bd0b9d082c58ad897b4562ffe6822e585 (diff) | |
download | st-patched-f210ea26c444607980d5de17ed7d4e62bb813631.tar.bz2 st-patched-f210ea26c444607980d5de17ed7d4e62bb813631.tar.xz st-patched-f210ea26c444607980d5de17ed7d4e62bb813631.zip |
Add info about Backspace and Delete to the FAQ
Diffstat (limited to 'FAQ')
-rw-r--r-- | FAQ | 58 |
1 files changed, 58 insertions, 0 deletions
@@ -98,3 +98,61 @@ If you want to compile st for OpenBSD you have to remove -lrt from config.mk, an | |||
98 | st will compile without any loss of functionality, because all the functions are | 98 | st will compile without any loss of functionality, because all the functions are |
99 | included in libc on this platform. | 99 | included in libc on this platform. |
100 | 100 | ||
101 | ## Backspace key does not work | ||
102 | |||
103 | This is an issue that was discussed in suckless mailing list | ||
104 | <http://lists.suckless.org/dev/1404/20697.html>: | ||
105 | |||
106 | Well, I am going to comment why I want to change the behaviour | ||
107 | of this key. When ascii was defined in 1968 communication | ||
108 | with computers were done using punched cards, or hardcopy | ||
109 | terminals (basically a typewritter machine connected with | ||
110 | the computer using a serial port). Due to this, ascii defines | ||
111 | DELETE as 7F, because in the puched cards, it means all the | ||
112 | holes of the card punched, so it is a kind of 'phisical | ||
113 | delete'. In the same way, BACKSPACE key was a non destructive | ||
114 | back space, as in typewriter machines. So, if you wanted | ||
115 | to delete a character, you had to BACKSPACE and then DELETE. | ||
116 | Other use of BACKSPACE was accented characters, for example | ||
117 | 'a BACKSPACE `'. The VT100 had no BACKSPACE key, it was | ||
118 | generated using the CONTROL key as another control character | ||
119 | (CONTROL key sets to 0 b7 b6 b5, so it converts H (code | ||
120 | 0x48) into BACKSPACE (code 0x08)), but it had a DELETE key | ||
121 | in a similar position where BACKSPACE key is located today | ||
122 | in common PC keyboards. All the terminal emulators emulated | ||
123 | correctly the difference between these keys, and backspace | ||
124 | key generated a BACKSPACE (^H) and delete key generated a | ||
125 | DELETE (^?). | ||
126 | |||
127 | But the problem arised when Linus Torvald wrote Linux, and | ||
128 | he did that the virtual terminal (the terminal emulator | ||
129 | integrated in the kernel) returns a DELETE when backspace | ||
130 | was pressed, due to the fact of the key in that position | ||
131 | in VT100 was a delete key. This created a lot of problems | ||
132 | (you can see it in [1] and [2]), and how Linux became the | ||
133 | king, a lot of terminal emulators today generate a DELETE | ||
134 | when backspace key is pressed in order to avoid problems | ||
135 | with linux. It causes that the only way of generating a | ||
136 | BACKSPACE in these systems is using CONTROL + H. I also | ||
137 | think that emacs had an important point here because CONTROL | ||
138 | + H prefix is used in emacs in some commands (help commands). | ||
139 | |||
140 | From point of view of the kernel, you can change the key | ||
141 | for deleting a previous character with stty erase. When you | ||
142 | connect a real terminal into a machine you describe the | ||
143 | type of terminal, so getty configure the correct value of | ||
144 | stty erase for this terminal, but in the case of terminal | ||
145 | emulators you don't have any getty that can set the correct | ||
146 | value of stty erase, so you always get the default value. | ||
147 | So it means that in case of changing the value of the | ||
148 | backspace keyboard, you have to add a 'stty erase ^H' into | ||
149 | your profile. Of course, other solution can be that st | ||
150 | itself modify the value of stty erase. I have usually the | ||
151 | inverse problem, when I connect with non Unix machines, and | ||
152 | I have to press control + h to get a BACKSPACE, or the | ||
153 | inverse, when a user connects to my unix machines from a | ||
154 | different system with a correct backspace key. | ||
155 | |||
156 | [1] http://www.ibb.net/~anne/keyboard.html | ||
157 | [2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html | ||
158 | |||