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General Purpose PostScript Generating Utility

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4.10.2 Guide Line for Delegations

First of all, select carefully the applications you will use for the delegations. If a filter is known to cause problems, try to avoid it in delegations(4). As a thumb rule, you should check that the PostScript generating applications produce files that start by:
 
%!PS-Adobe-3.0

a2ps needs the `%%BeginSetup'-`%%EndSetup' section in order to output correctly the page device definitions. It can happen that your filters don't output this section. In that case, you should insert a call to fixps right after the PostScript generation:
 
########## ROFF files
# Pass the roff files to groff.  Ask grog how groff should be called.
# Use fixps to ensure there is a %%BeginSetup/%%EndSetup section.
Delegation: Groff roff:ps	\
   eval `grog -Tps '$f'` | fixps #?V!!-q! | #{d.psselect} | #{d.psnup}

There are some services expected from the delegations. The delegations you may write should honor:

the input file
available via the escape `$f'. You should be aware that there are people who have great fun having spaces or dollars in their file names, so you probably should always use `'$f''. Some other variables are affected. Yes, I know, we need a special mechanism for `'' itself. Well, we'll see that later `;-)'.

the medium
the dimension of the medium selected by the user are available through `#w' and `#h'.

the page layout
the number of virtual pages is `#v'.

the page range
the page range (in a form `1-2,4-6,10-' for instance) is available by `#p'.

the verbosity level
please, do not make your delegations verbose by default. The silent mode should always be requested, unless `#?V' is set (see the above example with groff).

If ever you need several commands, do not use `;' to separate them, since it may prevent detection of failure. Use `&&' instead.

The slogan "the sooner, the better" should be applied here: in the processing chain, it is better to ask a service to the first application that supports it. An example will make it clear: when processing a DVI file, dvips knows better the page numbers than psselect would. So a DVI to PostScript delegation should ask the page selection (`#p') to dvips, instead of using psselect later in the chain. An other obvious reason here is plain efficiency (globally, less data is processed).


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