I think the simple summary "anything that screws up emacs users is good" pretty much says it all.
Johnny Robert Elz <k...@munnari.oz.au> skrev: (19 juli 2021 19:45:14 CEST) > Date: Mon, 19 Jul 2021 08:49:31 -0400 > From: Greg Troxel <g...@lexort.com> > Message-ID: <rmilf62a2p0....@s1.lexort.com> > > | As additional background, IMHO all of this confusion arose from the > | differing setups of DEC computers and the IBM PC. > >It is older than that. > > | On a real terminal as > | one would have used with a PDP-11 or VAX in the 70s/80s/early-90s, > >"Real terminals" existed long before PDP-11's or VAXen. They had keys >that struck paper and made marks. > >On those backspace moved backwards a character, and typing something >else >overstruck the previous character (sometimes intentionally, often just >making a mess). Delete did nothing at all. > >Some of those paper terminals also had paper tape punches and readers. >This allowed "off line" preparation of input, or messages (these >terminals >were used for telex / telegraph type operations, more than computers, >computers just needed something for interactive input, that is >something >different than punched cards, and these were available). > >When preparing a punched paper tape, to erase a mistaken character, one >relied on "delete does nothing" along with "delete is 0x7f", which when >converted to even parity format, is 0xFF, and since a "1" was recorded >on >the tape as a hole, punching a delete changed whatever was there before >into the delete code (all rows punched), which, as above, did nothing. >But to overstrike the previous character, one needed first to move >backwards >to be over it - that was what a "backspace" accomplished. > >So, on "real terminals" the sequence to erase the previous character >was >"backspace delete", and yes, the user had to type both of them - and to >erase two characters, one needed backspace backspace delete delete >(etc). > >When "glass ttys" started to become popular, their manufacturers >initially provided both keys - but computer systems wouldn't require >users to type both chars, but different systems picked differently. >Some used DEL (most Digital OS's did that), others used BSP (most >other systems, since that was the thing that worked easiest on a glass >tty - overstriking was destructive, so to replace one char with another >one simply did "backspace, replacement". But DEC had settled on DEL >as the preferred choice before glass ttys (or the "modern" form, >Tektronix >had a storage scope kind of thing, which was more like a paper >terminal, >just without paper) were invented. > >Unix used # for the erase character, as on a paper terminal you could >see >that, count how many # chars, and mentally erase that number of >previous >other characters (and @ was the line kill character, DEL was >"interrupt"). > >Many unix users (but not all) had come from a DEC background, and in >particular >a lot of BSD users, where there was "VMS vs BSD unix" type competition >all over >the place. So when BSD changed the defaults from # and @, they picked >the >DEC convention (DEL ^U ^C) - which irritated non-DEC users a bit (like >me) >who used non-DEC glass terminals, with BSP in a convenient location, >and DEL >somewhere obscure (more obscure, usually smaller key). Never mind, it >was >user configurable (had been since the very early days, at least for >erase and >kill - interrupt and quit were not configurable initially - which was >one >reason many people in the early days used BSP for erase, DEL remained >hard >wired as interrupt). > >| That led, I think, i386 unix (386BSD, then early NetBSD) to let the >key > | send ^H and configure erase to ^H, breaking emacs > >That alone IMO is the biggest feature. Anything that breaks emacs, >even in >trivial ways like this, is GOOD. > > | I don't see that as possible, and I have no idea why you would want >| that. Once you have the key that is logically the delete key sending > | DEL as original ASCII intended, > >It certainly intended nothing of the kind, DEL was "deleted" just as >NUL >was "never entered" (empty space on the paper tape where nothing had >been >punched). Both were simply ignored and had no effect whatever (and so >could be used for padding characters after sending something which the >terminal would take a long time to execute, like carriage-return or >line >feed. > >If you ever actually used paper tape (I did) the last thing you'd ever >want >was for DEL to start being interpreted as anything other than "nothing >here". >On the other hand, as backspace never (usually) ever got onto the tape, >it changed its position instead, that one turns out to be a nice choice >for >the erase character (paper tapes don't need it - the erasing is already >done). > >That using ^H (BSP) as erase screws emacs users is just a bonus point. > > | What are you trying to > | accomplish with this? Or are you asking "is there some way to have > | multiple characters function as erase in the tty"? > >But that's a good question. The tty driver (which is all you get when >you're in cat - unlike in a program which uses libedit or readline, or >similar where all this is done in those libraries, or in the program >itself) >has exactly one erase character - you can set it to anything you like >(hopefully something you can type), but you only get one of them (and >one >line kill, one interrupt, one quit, one pause output, one restart it, >one >discard output, one signal stop (and one delayed version of that). > >kre -- Skickat från min Android-enhet med K-9 Mail. Ursäkta min fåordighet.
