200(0) Ancient UNIX Licenses

[norman at nose.cita.utoronto.ca]

Warren's note reminds me of a few other Y2K bugs I've spotted that affect
ancient UNIX:
- date: no way to set the date past 1999 unless in the present year,
because two-digit input.
- at and atrun: commands are stored in the spooling directory with names
of the form YY.DDD.HHMM.xx, where xx is a unique number.  This one is
trickier to fix, because the filename is already exactly 14 characters,
so there's no room for expansion.  (On V10, I just rewrote the programs
to use a simple UNIX time expressed as a decimal number.  A simpler solution
might be to print the year in hex.)
- Perhaps least consequential and most amusing: nroff and troff store the
year in a number register.  The manual says it contains `the last two
digits of the year,' and many macro packages assume that is true, but the
truth is that it contains (year-1900), the same as tm_year.  So, for example,
when I ran man on New Year's Day, I was told that the manual page had been
printed on 1/1/100.

I was about to fix the various troff macro packages when I noticed that
the manual implied that I shouldn't.  I asked Brian Kernighan for an opinion
(since the code and the manual were both last touched by him); he thinks the
best view is that the manual is just wrong and the macro packages should be
fixed.  \n(yr is a read-write register, so `.nr yr \n(yr+1900' is probably
the easiest fix, though Brian points out that it's not always the right one
(maybe you really wanted a two-digit year).  If anyone is interested I can
pass along a more detailed note from Brian.

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