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# 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:

1. 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.

2. 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.

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