27 Sep
2015
27 Sep
'15
8:12 p.m.
Mark Longridge <cubexyz(a)gmail.com> writes:
It seems that nroff had the ability to show underlined
text very early
on, possibly as early as v3 according to the v3 manual.
I haven't managed to get this to work right under simh but I was
thinking maybe there's a way to do it. It needs an 'underline font'
but the mechanism of how this worked in the old days is a bit of
mystery to me. The output device would have to have the ability to
either display or print underlined text. Maybe someone can remember
which terminal devices supported this in the old days which worked
"out of the box" in the v5,v6 era.
Maybe there was the ability to use overstrike characters on the teletype?
In bash I can use:
echo -e "\e[4munderline\e[0m"
The proper escape sequence to end underline is technically \e[24m; using
0 here ends all other formats (bold, color) as well.
Shouldn't be too hard to hack up something that
works in emulated v5.
The "ul" utility, which converts from overstrikes to termcap-based
escape sequences, first appeared in 3.0BSD.
The source code is here:
http://minnie.tuhs.org/cgi-bin/utree.pl?file=3BSD/usr/src/cmd/ul.c
It'd probably be pretty easy to rip out the termcap dependency and have
it just output ansi codes, though I don't know what dialect of C works
on v5.
1BSD to 3BSD also had an "iul" utility which just printed a row of
dashes under characters to be underlined instead of using escape
sequences. In 2.9BSD and 4BSD and later this functionality is provided
by "ul -i".
http://minnie.tuhs.org/cgi-bin/utree.pl?file=1BSD/s6/iul.c
It looks like this wouldn't be hard to modify to use escape sequences
instead, and it uses the oldest C dialect of any of these versions.
From 4.1c BSD, ul also handles bold, which is
represented by
self-overstriking in the nroff output, and represents superscript
and
subscript (half-linefeed) with dim attributes. Any missing attributes
are represented with standout. This is essentially the same
functionality available in modern versions of ul.