printing-advanced.html

FreeBSD操作系统的详细使用手册

name="PRINTING-ADVANCED-IF-CONVERSION">9.4.1.2 Accommodating Plain Text Jobs on <span
class="TRADEMARK">PostScript</span>&reg; Printers</a></h3>

<p>If you are the only user of your computer and <span
class="TRADEMARK">PostScript</span> (or other language-based) printer, and you promise to
never send plain text to your printer and to never use features of various programs that
will want to send plain text to your printer, then you do not need to worry about this
section at all.</p>

<p>But, if you would like to send both <span class="TRADEMARK">PostScript</span> and
plain text jobs to the printer, then you are urged to augment your printer setup. To do
so, we have the text filter detect if the arriving job is plain text or <span
class="TRADEMARK">PostScript</span>. All <span class="TRADEMARK">PostScript</span> jobs
must start with <var class="LITERAL">%!</var> (for other printer languages, see your
printer documentation). If those are the first two characters in the job, we have <span
class="TRADEMARK">PostScript</span>, and can pass the rest of the job directly. If those
are not the first two characters in the file, then the filter will convert the text into
<span class="TRADEMARK">PostScript</span> and print the result.</p>

<p>How do we do this?</p>

<p>If you have got a serial printer, a great way to do it is to install <tt
class="COMMAND">lprps</tt>. <tt class="COMMAND">lprps</tt> is a <span
class="TRADEMARK">PostScript</span> printer filter which performs two-way communication
with the printer. It updates the printer's status file with verbose information from the
printer, so users and administrators can see exactly what the state of the printer is
(such as ``<tt class="ERRORNAME">toner low</tt>'' or ``<tt class="ERRORNAME">paper
jam</tt>''). But more importantly, it includes a program called <tt
class="COMMAND">psif</tt> which detects whether the incoming job is plain text and calls
<tt class="COMMAND">textps</tt> (another program that comes with <tt
class="COMMAND">lprps</tt>) to convert it to <span class="TRADEMARK">PostScript</span>.
It then uses <tt class="COMMAND">lprps</tt> to send the job to the printer.</p>

<p><tt class="COMMAND">lprps</tt> is part of the FreeBSD Ports Collection (see <a
href="ports.html">The Ports Collection</a>). You can fetch, build and install it
yourself, of course. After installing <tt class="COMMAND">lprps</tt>, just specify the
pathname to the <tt class="COMMAND">psif</tt> program that is part of <tt
class="COMMAND">lprps</tt>. If you installed <tt class="COMMAND">lprps</tt> from the
ports collection, use the following in the serial <span
class="TRADEMARK">PostScript</span> printer's entry in <tt
class="FILENAME">/etc/printcap</tt>:</p>

<pre class="PROGRAMLISTING">
:if=/usr/local/libexec/psif:
</pre>

<p>You should also specify the <var class="LITERAL">rw</var> capability; that tells <b
class="APPLICATION">LPD</b> to open the printer in read-write mode.</p>

<p>If you have a parallel <span class="TRADEMARK">PostScript</span> printer (and
therefore cannot use two-way communication with the printer, which <tt
class="COMMAND">lprps</tt> needs), you can use the following shell script as the text
filter:</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  psif - Print PostScript or plain text on a PostScript printer
#  Script version; NOT the version that comes with lprps
#  Installed in /usr/local/libexec/psif
#

IFS="" read -r first_line
first_two_chars=`expr "$first_line" : '\(..\)'`

if [ "$first_two_chars" = "%!" ]; then
    #
    #  PostScript job, print it.
    #
    echo "$first_line" &amp;&amp; cat &amp;&amp; printf "\004" &amp;&amp; exit 0
    exit 2
else
    #
    #  Plain text, convert it, then print it.
    #
    ( echo "$first_line"; cat ) | /usr/local/bin/textps &amp;&amp; printf "\004" &amp;&amp; exit 0
    exit 2
fi
</pre>

<p>In the above script, <tt class="COMMAND">textps</tt> is a program we installed
separately to convert plain text to <span class="TRADEMARK">PostScript</span>. You can
use any text-to-<span class="TRADEMARK">PostScript</span> program you wish. The FreeBSD
Ports Collection (see <a href="ports.html">The Ports Collection</a>) includes a full
featured text-to-<span class="TRADEMARK">PostScript</span> program called <var
class="LITERAL">a2ps</var> that you might want to investigate.</p>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="PRINTING-ADVANCED-PS" name="PRINTING-ADVANCED-PS">9.4.1.3
Simulating <span class="TRADEMARK">PostScript</span> on Non <span
class="TRADEMARK">PostScript</span> Printers</a></h3>

<p><span class="TRADEMARK">PostScript</span> is the <span class="emphasis"><i
class="EMPHASIS">de facto</i></span> standard for high quality typesetting and printing.
<span class="TRADEMARK">PostScript</span> is, however, an <span class="emphasis"><i
class="EMPHASIS">expensive</i></span> standard. Thankfully, Aladdin Enterprises has a
free <span class="TRADEMARK">PostScript</span> work-alike called <b
class="APPLICATION">Ghostscript</b> that runs with FreeBSD. Ghostscript can read most
<span class="TRADEMARK">PostScript</span> files and can render their pages onto a variety
of devices, including many brands of non-PostScript printers. By installing Ghostscript
and using a special text filter for your printer, you can make your non <span
class="TRADEMARK">PostScript</span> printer act like a real <span
class="TRADEMARK">PostScript</span> printer.</p>

<p>Ghostscript is in the FreeBSD Ports Collection, if you would like to install it from
there. You can fetch, build, and install it quite easily yourself, as well.</p>

<p>To simulate <span class="TRADEMARK">PostScript</span>, we have the text filter detect
if it is printing a <span class="TRADEMARK">PostScript</span> file. If it is not, then
the filter will pass the file directly to the printer; otherwise, it will use Ghostscript
to first convert the file into a format the printer will understand.</p>

<p>Here is an example: the following script is a text filter for Hewlett Packard DeskJet
500 printers. For other printers, substitute the <var class="OPTION">-sDEVICE</var>
argument to the <tt class="COMMAND">gs</tt> (Ghostscript) command. (Type <tt
class="COMMAND">gs -h</tt> to get a list of devices the current installation of
Ghostscript supports.)</p>

<pre class="PROGRAMLISTING">
#!/bin/sh
#
#  ifhp - Print Ghostscript-simulated PostScript on a DeskJet 500
#  Installed in /usr/local/libexec/ifhp

#
#  Treat LF as CR+LF (to avoid the "staircase effect" on HP/PCL
#  printers):
#
printf "\033&amp;k2G" || exit 2

#
#  Read first two characters of the file
#
IFS="" read -r first_line
first_two_chars=`expr "$first_line" : '\(..\)'`

if [ "$first_two_chars" = "%!" ]; then
    #
    #  It is PostScript; use Ghostscript to scan-convert and print it.
    #
    /usr/local/bin/gs -dSAFER -dNOPAUSE -q -sDEVICE=djet500 \
      -sOutputFile=- - &amp;&amp; exit 0
else
    #
    #  Plain text or HP/PCL, so just print it directly; print a form feed
    #  at the end to eject the last page.
    #
    echo "$first_line" &amp;&amp; cat &amp;&amp; printf "\033&amp;l0H" &amp;&amp; 
exit 0
fi

exit 2
</pre>

<p>Finally, you need to notify <b class="APPLICATION">LPD</b> of the filter via the <var
class="LITERAL">if</var> capability:</p>

<pre class="PROGRAMLISTING">
:if=/usr/local/libexec/ifhp:
</pre>

<p>That is it. You can type <tt class="COMMAND">lpr plain.text</tt> and <tt
class="FILENAME">lpr whatever.ps</tt> and both should print successfully.</p>
</div>

<div class="SECT3">
<h3 class="SECT3"><a id="PRINTING-ADVANCED-CONVFILTERS"
name="PRINTING-ADVANCED-CONVFILTERS">9.4.1.4 Conversion Filters</a></h3>

<p>After completing the simple setup described in <a
href="printing-intro-setup.html#PRINTING-SIMPLE">Simple Printer Setup</a>, the first
thing you will probably want to do is install conversion filters for your favorite file
formats (besides plain ASCII text).</p>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN11415" name="AEN11415">9.4.1.4.1 Why Install Conversion
Filters?</a></h4>

<p>Conversion filters make printing various kinds of files easy. As an example, suppose
we do a lot of work with the <b class="APPLICATION">TeX</b> typesetting system, and we
have a <span class="TRADEMARK">PostScript</span> printer. Every time we generate a DVI
file from <b class="APPLICATION">TeX</b>, we cannot print it directly until we convert
the DVI file into <span class="TRADEMARK">PostScript</span>. The command sequence goes
like this:</p>

<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">dvips seaweed-analysis.dvi</kbd>
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">lpr seaweed-analysis.ps</kbd>
</pre>

<p>By installing a conversion filter for DVI files, we can skip the hand conversion step
each time by having <b class="APPLICATION">LPD</b> do it for us. Now, each time we get a
DVI file, we are just one step away from printing it:</p>

<pre class="SCREEN">
<samp class="PROMPT">%</samp> <kbd class="USERINPUT">lpr -d seaweed-analysis.dvi</kbd>
</pre>

<p>We got <b class="APPLICATION">LPD</b> to do the DVI file conversion for us by
specifying the <var class="OPTION">-d</var> option. Section <a
href="printing-using.html#PRINTING-LPR-OPTIONS-FORMAT">Formatting and Conversion
Options</a> lists the conversion options.</p>

<p>For each of the conversion options you want a printer to support, install a <span
class="emphasis"><i class="EMPHASIS">conversion filter</i></span> and specify its
pathname in <tt class="FILENAME">/etc/printcap</tt>. A conversion filter is like the text
filter for the simple printer setup (see section <a
href="printing-intro-setup.html#PRINTING-TEXTFILTER">Installing the Text Filter</a>)
except that instead of printing plain text, the filter converts the file into a format
the printer can understand.</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN11444" name="AEN11444">9.4.1.4.2 Which Conversions Filters
Should I Install?</a></h4>

<p>You should install the conversion filters you expect to use. If you print a lot of DVI
data, then a DVI conversion filter is in order. If you have got plenty of troff to print
out, then you probably want a troff filter.</p>

<p>The following table summarizes the filters that <b class="APPLICATION">LPD</b> works
with, their capability entries for the <tt class="FILENAME">/etc/printcap</tt> file, and
how to invoke them with the <tt class="COMMAND">lpr</tt> command:</p>

<div class="INFORMALTABLE"><a id="AEN11451" name="AEN11451"></a>
<table border="0" frame="void" class="CALSTABLE">
<col />
<col />
<col />
<thead>
<tr>
<th>File type</th>
<th><tt class="FILENAME">/etc/printcap</tt> capability</th>
<th><tt class="COMMAND">lpr</tt> option</th>
</tr>
</thead>

<tbody>
<tr>
<td>cifplot</td>
<td><var class="LITERAL">cf</var></td>
<td><var class="OPTION">-c</var></td>
</tr>

<tr>
<td>DVI</td>
<td><var class="LITERAL">df</var></td>
<td><var class="OPTION">-d</var></td>
</tr>

<tr>
<td>plot</td>
<td><var class="LITERAL">gf</var></td>
<td><var class="OPTION">-g</var></td>
</tr>

<tr>
<td>ditroff</td>
<td><var class="LITERAL">nf</var></td>
<td><var class="OPTION">-n</var></td>
</tr>

<tr>
<td>FORTRAN text</td>
<td><var class="LITERAL">rf</var></td>
<td><var class="OPTION">-f</var></td>
</tr>

<tr>
<td>troff</td>
<td><var class="LITERAL">tf</var></td>
<td><var class="OPTION">-f</var></td>
</tr>

<tr>
<td>raster</td>
<td><var class="LITERAL">vf</var></td>
<td><var class="OPTION">-v</var></td>
</tr>

<tr>
<td>plain text</td>
<td><var class="LITERAL">if</var></td>
<td>none, <var class="OPTION">-p</var>, or <var class="OPTION">-l</var></td>
</tr>
</tbody>
</table>
</div>

<p>In our example, using <tt class="COMMAND">lpr -d</tt> means the printer needs a <var
class="LITERAL">df</var> capability in its entry in <tt
class="FILENAME">/etc/printcap</tt>.</p>

<p>Despite what others might contend, formats like FORTRAN text and plot are probably
obsolete. At your site, you can give new meanings to these or any of the formatting
options just by installing custom filters. For example, suppose you would like to
directly print Printerleaf files (files from the Interleaf desktop publishing program),
but will never print plot files. You could install a Printerleaf conversion filter under
the <var class="LITERAL">gf</var> capability and then educate your users that <tt
class="COMMAND">lpr -g</tt> mean ``print Printerleaf files.''</p>
</div>

<div class="SECT4">
<h4 class="SECT4"><a id="AEN11520" name="AEN11520">9.4.1.4.3 Installing Conversion
Filters</a></h4>

<p>Since conversion filters are programs you install outside of the base FreeBSD
installation, they should probably go under <tt class="FILENAME">/usr/local</tt>. The
directory <tt class="FILENAME">/usr/local/libexec</tt> is a popular location, since they
are specialized programs that only <b class="APPLICATION">LPD</b> will run; regular users
should not ever need to run them.</p>

<p>To enable a conversion filter, specify its pathname under the appropriate capability
for the destination printer in <tt class="FILENAME">/etc/printcap</tt>.</p>