printing-advanced.html

FreeBSD操作系统的详细使用手册

<p>In our example, we will add the DVI conversion filter to the entry for the printer
named <var class="LITERAL">bamboo</var>. Here is the example <tt
class="FILENAME">/etc/printcap</tt> file again, with the new <var
class="LITERAL">df</var> capability for the printer <var
class="LITERAL">bamboo</var>.</p>

<pre class="PROGRAMLISTING">
#
#  /etc/printcap for host rose - added df filter for bamboo
#
rattan|line|diablo|lp|Diablo 630 Line Printer:\
        :sh:sd=/var/spool/lpd/rattan:\
        :lp=/dev/lpt0:\
        :if=/usr/local/libexec/if-simple:

bamboo|ps|PS|S|panasonic|Panasonic KX-P4455 PostScript v51.4:\
        :sh:sd=/var/spool/lpd/bamboo:\
        :lp=/dev/ttyd5:ms#-parenb cs8 clocal crtscts:rw:\
        :if=/usr/local/libexec/psif:\
        :df=/usr/local/libexec/psdf:
</pre>

<p>The DVI filter is a shell script named <tt
class="FILENAME">/usr/local/libexec/psdf</tt>. Here is that script:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  psdf - DVI to PostScript printer filter
#  Installed in /usr/local/libexec/psdf
#
# Invoked by lpd when user runs lpr -d
#
exec /usr/local/bin/dvips -f | /usr/local/libexec/lprps "$@"
</pre>

<p>This script runs <tt class="COMMAND">dvips</tt> in filter mode (the <var
class="OPTION">-f</var> argument) on standard input, which is the job to print. It then
starts the <span class="TRADEMARK">PostScript</span> printer filter <tt
class="COMMAND">lprps</tt> (see section <a
href="printing-advanced.html#PRINTING-ADVANCED-IF-CONVERSION">Accommodating Plain Text
Jobs on <span class="TRADEMARK">PostScript</span> Printers</a>) with the arguments <b
class="APPLICATION">LPD</b> passed to this script. <tt class="COMMAND">lprps</tt> will
use those arguments to account for the pages printed.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN11546" name="AEN11546">9.4.1.4.4 More Conversion Filter
Examples</a></h4>

<p>Since there is no fixed set of steps to install conversion filters, let me instead
provide more examples. Use these as guidance to making your own filters. Use them
directly, if appropriate.</p>

<p>This example script is a raster (well, GIF file, actually) conversion filter for a
Hewlett Packard LaserJet III-Si printer:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  hpvf - Convert GIF files into HP/PCL, then print
#  Installed in /usr/local/libexec/hpvf
                  
PATH=/usr/X11R6/bin:$PATH; export PATH
giftopnm | ppmtopgm | pgmtopbm | pbmtolj -resolution 300 \
    &amp;&amp; exit 0 \
    || exit 2
</pre>

<p>It works by converting the GIF file into a portable anymap, converting that into a
portable graymap, converting that into a portable bitmap, and converting that into
LaserJet/PCL-compatible data.</p>

<p>Here is the <tt class="FILENAME">/etc/printcap</tt> file with an entry for a printer
using the above filter:</p>

<pre class="PROGRAMLISTING">
#
#  /etc/printcap for host orchid
#
teak|hp|laserjet|Hewlett Packard LaserJet 3Si:\
        :lp=/dev/lpt0:sh:sd=/var/spool/lpd/teak:mx#0:\
        :if=/usr/local/libexec/hpif:\
        :vf=/usr/local/libexec/hpvf:
</pre>

<p>The following script is a conversion filter for troff data from the groff typesetting
system for the <span class="TRADEMARK">PostScript</span> printer named <var
class="LITERAL">bamboo</var>:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  pstf - Convert groff's troff data into PS, then print.
#  Installed in /usr/local/libexec/pstf
#
exec grops | /usr/local/libexec/lprps "$@"
</pre>

<p>The above script makes use of <tt class="COMMAND">lprps</tt> again to handle the
communication with the printer. If the printer were on a parallel port, we would use this
script instead:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  pstf - Convert groff's troff data into PS, then print.
#  Installed in /usr/local/libexec/pstf
#
exec grops
</pre>

<p>That is it. Here is the entry we need to add to <tt
class="FILENAME">/etc/printcap</tt> to enable the filter:</p>

<pre class="PROGRAMLISTING">
:tf=/usr/local/libexec/pstf:
</pre>

<p>Here is an example that might make old hands at FORTRAN blush. It is a FORTRAN-text
filter for any printer that can directly print plain text. We will install it for the
printer <var class="LITERAL">teak</var>:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
# hprf - FORTRAN text filter for LaserJet 3si:
# Installed in /usr/local/libexec/hprf
#

printf "\033&amp;k2G" &amp;&amp; fpr &amp;&amp; printf "\033&amp;l0H" &amp;&amp;
 exit 0
exit 2
</pre>

<p>And we will add this line to the <tt class="FILENAME">/etc/printcap</tt> for the
printer <var class="LITERAL">teak</var> to enable this filter:</p>

<pre class="PROGRAMLISTING">
:rf=/usr/local/libexec/hprf:
</pre>

<p>Here is one final, somewhat complex example. We will add a DVI filter to the LaserJet
printer <var class="LITERAL">teak</var> introduced earlier. First, the easy part:
updating <tt class="FILENAME">/etc/printcap</tt> with the location of the DVI filter:</p>

<pre class="PROGRAMLISTING">
:df=/usr/local/libexec/hpdf:
</pre>

<p>Now, for the hard part: making the filter. For that, we need a DVI-to-LaserJet/PCL
conversion program. The FreeBSD Ports Collection (see <a href="ports.html">The Ports
Collection</a>) has one: <tt class="COMMAND">dvi2xx</tt> is the name of the package.
Installing this package gives us the program we need, <tt class="COMMAND">dvilj2p</tt>,
which converts DVI into LaserJet IIp, LaserJet III, and LaserJet 2000 compatible
codes.</p>

<p><tt class="COMMAND">dvilj2p</tt> makes the filter <tt class="COMMAND">hpdf</tt> quite
complex since <tt class="COMMAND">dvilj2p</tt> cannot read from standard input. It wants
to work with a filename. What is worse, the filename has to end in <tt
class="FILENAME">.dvi</tt> so using <tt class="FILENAME">/dev/fd/0</tt> for standard
input is problematic. We can get around that problem by linking (symbolically) a
temporary file name (one that ends in <tt class="FILENAME">.dvi</tt>) to <tt
class="FILENAME">/dev/fd/0</tt>, thereby forcing <tt class="COMMAND">dvilj2p</tt> to read
from standard input.</p>

<p>The only other fly in the ointment is the fact that we cannot use <tt
class="FILENAME">/tmp</tt> for the temporary link. Symbolic links are owned by user and
group <tt class="USERNAME">bin</tt>. The filter runs as user <tt
class="USERNAME">daemon</tt>. And the <tt class="FILENAME">/tmp</tt> directory has the
sticky bit set. The filter can create the link, but it will not be able clean up when
done and remove it since the link will belong to a different user.</p>

<p>Instead, the filter will make the symbolic link in the current working directory,
which is the spooling directory (specified by the <var class="LITERAL">sd</var>
capability in <tt class="FILENAME">/etc/printcap</tt>). This is a perfect place for
filters to do their work, especially since there is (sometimes) more free disk space in
the spooling directory than under <tt class="FILENAME">/tmp</tt>.</p>

<p>Here, finally, is the filter:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  hpdf - Print DVI data on HP/PCL printer
#  Installed in /usr/local/libexec/hpdf

PATH=/usr/local/bin:$PATH; export PATH

#
#  Define a function to clean up our temporary files.  These exist
#  in the current directory, which will be the spooling directory
#  for the printer.
#
cleanup() {
   rm -f hpdf$$.dvi
}

#
#  Define a function to handle fatal errors: print the given message
#  and exit 2.  Exiting with 2 tells LPD to do not try to reprint the
#  job.
#
fatal() {
    echo "$@" 1&gt;&amp;2
    cleanup
    exit 2
}

#
#  If user removes the job, LPD will send SIGINT, so trap SIGINT
#  (and a few other signals) to clean up after ourselves.
#
trap cleanup 1 2 15 

#
#  Make sure we are not colliding with any existing files.
#
cleanup

#
#  Link the DVI input file to standard input (the file to print).
#
ln -s /dev/fd/0 hpdf$$.dvi || fatal "Cannot symlink /dev/fd/0"

#
#  Make LF = CR+LF
#
printf "\033&amp;k2G" || fatal "Cannot initialize printer"

# 
#  Convert and print.  Return value from dvilj2p does not seem to be
#  reliable, so we ignore it.
#
dvilj2p -M1 -q -e- dfhp$$.dvi

#
#  Clean up and exit
#
cleanup
exit 0
</pre>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="PRINTING-ADVANCED-AUTOCONV"
name="PRINTING-ADVANCED-AUTOCONV">9.4.1.4.5 Automated Conversion: an Alternative to
Conversion Filters</a></h4>

<p>All these conversion filters accomplish a lot for your printing environment, but at
the cost forcing the user to specify (on the <a
href="http://www.FreeBSD.org/cgi/man.cgi?query=lpr&sektion=1"><span
class="CITEREFENTRY"><span class="REFENTRYTITLE">lpr</span>(1)</span></a> command line)
which one to use. If your users are not particularly computer literate, having to specify
a filter option will become annoying. What is worse, though, is that an incorrectly
specified filter option may run a filter on the wrong type of file and cause your printer
to spew out hundreds of sheets of paper.</p>

<p>Rather than install conversion filters at all, you might want to try having the text
filter (since it is the default filter) detect the type of file it has been asked to
print and then automatically run the right conversion filter. Tools such as <tt
class="COMMAND">file</tt> can be of help here. Of course, it will be hard to determine
the differences between <span class="emphasis"><i class="EMPHASIS">some</i></span> file
types--and, of course, you can still provide conversion filters just for them.</p>

<p>The FreeBSD Ports Collection has a text filter that performs automatic conversion
called <tt class="COMMAND">apsfilter</tt>. It can detect plain text, <span
class="TRADEMARK">PostScript</span>, and DVI files, run the proper conversions, and
print.</p>
</div>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="PRINTING-ADVANCED-OF" name="PRINTING-ADVANCED-OF">9.4.1.5 Output
Filters</a></h3>

<p>The <b class="APPLICATION">LPD</b> spooling system supports one other type of filter
that we have not yet explored: an output filter. An output filter is intended for
printing plain text only, like the text filter, but with many simplifications. If you are
using an output filter but no text filter, then:</p>

<ul>
<li>
<p><b class="APPLICATION">LPD</b> starts an output filter once for the entire job instead
of once for each file in the job.</p>
</li>

<li>
<p><b class="APPLICATION">LPD</b> does not make any provision to identify the start or
the end of files within the job for the output filter.</p>
</li>

<li>
<p><b class="APPLICATION">LPD</b> does not pass the user's login or host to the filter,
so it is not intended to do accounting. In fact, it gets only two arguments:</p>

<p><tt class="COMMAND">filter-name</tt> -w<var class="REPLACEABLE">width</var> -l<var
class="REPLACEABLE">length</var></p>

<p>Where <var class="REPLACEABLE">width</var> is from the <var class="LITERAL">pw</var>
capability and <var class="REPLACEABLE">length</var> is from the <var
class="LITERAL">pl</var> capability for the printer in question.</p>
</li>
</ul>

<p>Do not be seduced by an output filter's simplicity. If you would like each file in a
job to start on a different page an output filter <span class="emphasis"><i
class="EMPHASIS">will not work</i></span>. Use a text filter (also known as an input
filter); see section <a href="printing-intro-setup.html#PRINTING-TEXTFILTER">Installing
the Text Filter</a>. Furthermore, an output filter is actually <span class="emphasis"><i
class="EMPHASIS">more complex</i></span> in that it has to examine the byte stream being
sent to it for special flag characters and must send signals to itself on behalf of <b
class="APPLICATION">LPD</b>.</p>