Re: [Groff] conditional logic based on device?

[Clarke Echols]

Michael(tm) Smith wrote:
> Werner LEMBERG <address@hidden>, 2008-02-20 18:53 +0100:
>
> > > >  >     .if n         \" for nroff processing input
> > > >
> > > >  >     .if t         \" for troff/groff processing input
> > > I read the groff info node about conditionals, but just didn't know
> > > how to specify a condition that would only affect console output.
> > Hmm.  groff.texinfo has an index entry for `nroff mode' which points
> > to section named `Troff and Nroff Mode', and which explains the
> > differences.  Anyway, I'll add links.
>
> OK, I did now read the following in the that node:
>
>   "Originally, `nroff' and `troff' were two separate programs, the
>   former for TTY output, the latter for everything else. [...] it
>   is sometimes necessary to make a distinction between TTY and
>   non-TTY devices: `gtroff' provides two built-in conditions `n'
>   and `t' for the `if', `ie', and `while' requests to decide
>   whether `gtroff' shall behave like `nroff' or like `troff'."

I was not aware that groff had both conditionals.  The correct
classic behavior would be for troff to ignore anything following
the ".if n" conditional, and nroff would ignore input associated
with ".if t" .

I learned about it when modifying the man macros for producing the
HP-UX man pages.  I once told a co-worker if one wants to learn and 
understand troff (groff), a good way would be to take a completely
uncommented man macro file (or mm, ms, me, etc.) and convert it into
a completely commented file where every operation is fully explained,
and do it without breaking any macros.  That's essentially how I
learned it.

Clarke