🚀 go-pugleaf

In article <7813@exodus.Eng.Sun.COM> tut@cairo.Eng.Sun.COM (Bill "Bill" Tuthill) writes:
>The world's three most important operating systems-- Unix, MS-DOS,
>and MacOS-- all employ different methods for separating lines from
>each other.  Unix uses linefeed only, MS-DOS uses carriage return
>and linefeed, and MacOS uses carriage return only.
>
>My question is this: do any standards specify how lines should be
>kept apart?  That is, do any of these three operating systems have
>any justification (other than space savings in the case of Unix and
>MacOS) for doing things they way they did?

I don't have copies of all the relevant standards, but I have read
most of them in the past, so here's the situataion as I understand it.

Prior to ISO Latin-1, there was no single character whose semantics was
that of "line separator", since the ANSI standards did not contain the
concept of a line.  Carriage return was exactly that: move the active
position to the beginning of the line.  Line feed was exactly that:
move the active position to the next line down.  Many systems therefore
used CR-LF as a "newline" indicator.  I seem to recall that use of
Line Feed alone was a permissible option under the original ANSI
standard, but that usage is now deprecated.  This make MS-DOS(!) the
most correct, Unix correct but outdated, and MacOS completely out of
it.  In defense of the Mac, I'll just point out that its much easier to
deal with file conversion when a single character is used as a line
separator.  There are some messy situations you can get into with the
MS-DOS to Unix conversion.

ASCII does define some separator characters: File Sep., Group Sep.,
Record Sep., and Unit Sep., but no semantics were given for these.  If
they are used hierarchically, then files contain groups which contain
records which contain units, but beyond that, the meaning is
"application specific".  It would have been reasonable to use Record
Separator to be a "newline" but I don't think anyone has.  One terminal
I worked with used Unit Separator as a newline.

I should also point out that there are no characters in 7-bit ASCII
whose meaning is "ignore the last character I sent".  Most systems use
Backspace or Delete for this, and neither mean that.  Backspace means
"move the active position backward by one", and delete is a no-op,
which should be ignored.  (Originally, delete characters were used to
erase, or "rub-out" mistyped characters in punched tape.  This is why
Delete is all 1s: it punched out all the holes in paper tape,
obliterating the mistyped character!)  The "cancel" character might have
been used, since it has a generalized meaning of "oops!".  Also there
is no line kill character, i.e., one that means "forget everything since
the last newline".  How could there be, when there is no concept of a
line!

Latin-1 has fixed some of that, but I doubt the fixes will ever be
popular.  In the C1 control set there is a character NEL, which means
Next Line, and is a proper newline character.  There is also a
character (CCH, I *think*) which means "ignore the last character
sent".  I don't think there is a "line kill" character, though.
The VT420 on my desk can handle NEL, but not CCH.

Things to read are ANSI X3.64, X3.134.* and the various ISO standards.

If I got any of this wrong, my apologies, and please send me mail,
so I don't do it again!

Jim
Spoken: Jim Williams             Domain: williams@nssdcs.gsfc.nasa.gov
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