6. What preprocessors may I
use?
Groff comes with at least three preprocessors,
tbl, eqn, and
pic (on some systems they are named
gtbl, geqn and
gpic.) Their purpose is to translate
preprocessor macros and their data to regular troff input.
Tbl is a table preprocessor,
eqn is an equations/maths preprocessor and
pic is a picture preprocessor. Please refer to
the man pages for more information on what functionality they
provide. To put it in a nutshell: don't write man pages
requiring any preprocessor. Eqn will generally
produce terrible output for typewriter-like devices, unfortunately
the type of device 99% of all man pages are viewed on (well, at
least I do). For example, XAllocColor.3x uses a few formulas with
exponentiation. Due to the nature of typewriter-like devices, the
exponent will be on the same line as the base. N to the power of
two appears as `N2'. Tbl should be avoided
because all xman programs I have seen fail on them. Xman 3.1.6 uses
the following command to format man pages, e.g. signal(7):
gtbl /usr/man/man7/signal.7 | geqn | gtbl | groff
-Tascii -man /tmp/xmana01760 2> /dev/null
which screws up for sources using gtbl,
because gtbl output is fed again into
gtbl. The effect is a man page without your
table. I don't know if it's a bug or a feature that
gtbl chokes on its own output or if xman could
be a little smarter and not use gtbl twice.
Furthermore, some systems use grog to determine
what options to pass to groff. Unfortunately grog sometimes guesses
wrong and recommends groff -t when in fact
tbl must not be used. We are basically left with
two workarounds for tables:
Format the table yourself manually and put it between .nf and
.fi lines so that it will be left unformatted. You won't have
bold and italics this way but this beats having your table
swallowed any day.
Use any tbl macros you like but distribute
the tbl output instead of the input. There is
however this quirk with grog who thinks that any
file containing a line starting with .TS
requires tbl. Tbl output for
some reason unbeknownst to me still contains .TS
and .TE. It seems you can simply remove them and
have the result still look okay. YMMV, so please test this with
your particular man page.
I have yet to see a man page requiring pic
preprocessing. But I would not like it. As you can see above,
xman will not use it and
groff will certainly do the funky wadakiki on
the input.
Free eBook: 
