(a2ps.info)Guide Line for Delegations

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4.10.2 Guide Line for Delegations
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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(1).  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).

   ---------- Footnotes ----------

   (1) Because hiding its use into 'a2ps' just makes it even more
difficult to the users to know why it failed.  Let them use it by hand.