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<th colspan="3" align="center">LPRng-HOWTO: 1 Apr 2002
(For LPRng-3.8.10)</th>
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<tr>
<td width="10%" align="left" valign="bottom"><a href=
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<td width="80%" align="center" valign="bottom">Chapter
16. Filters</td>
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<div class="SECT1">
<h1 class="SECT1"><a name="FILTEROPTIONS">16.8. Filter
Command Line Options and Environment Variables</a></h1>
<p>Options used:</p>
<ul>
<li>
<p><tt class="LITERAL">bk_filter_options=</tt><i class=
"EMPHASIS">Backwards Compatible Filter options</i></p>
</li>
<li>
<p><tt class="LITERAL">bk_of_filter_options=</tt><i
class="EMPHASIS">Backwards Compatible OF Filter
options</i></p>
</li>
<li>
<p><tt class="LITERAL">bkf</tt> FLAG <i class=
"EMPHASIS">Backwards Compatible Filters</i></p>
</li>
<li>
<p><tt class="LITERAL">filter_ld_path=</tt><i class=
"EMPHASIS">Filter LD_LIBRARY_PATH environment</i></p>
</li>
<li>
<p><tt class="LITERAL">filter_options=</tt><i class=
"EMPHASIS">Filter options</i></p>
</li>
<li>
<p><tt class="LITERAL">filter_path=</tt><i class=
"EMPHASIS">Filter PATH environment</i></p>
</li>
<li>
<p><tt class="LITERAL">of_filter_options=</tt><i class=
"EMPHASIS">OF Filter options</i></p>
</li>
<li>
<p><tt class="LITERAL">pass_env=</tt><i class=
"EMPHASIS">Environment variables to copy to Filter
environment</i></p>
</li>
<li>
<p><tt class="LITERAL">pl=</tt><i class="EMPHASIS">line
count for page</i></p>
</li>
<li>
<p><tt class="LITERAL">pw=</tt><i class="EMPHASIS">column
count for page</i></p>
</li>
<li>
<p><tt class="LITERAL">px=</tt><i class="EMPHASIS">pixel
width for page</i></p>
</li>
<li>
<p><tt class="LITERAL">py=</tt><i class="EMPHASIS">pixel
length for page</i></p>
</li>
</ul>
<br>
<br>
<p>A filter (or program) specification in the <b class=
"APPLICATION">LPRng</b> printcap database has the form:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN7937"></a>
<pre class="SCREEN">
:option=| [flags] /path [argument | "argument" | 'argument' ]*
:option=[flags] /path [argument | "argument" | 'argument' ]*
</pre>
</div>
<br>
<br>
<p>The first case is used where the option value can be a
string or filter, and the second where a program is always
expected. The following procedure is used to run a filter
program. Arguments in single or double quotes are passed as a
single value, as for a shell.</p>
<p>The sequence of operations to run a filter is as
follows:</p>
<ol type="1">
<li>
<p>The program must be specified with an absolute path
name.</p>
</li>
<li>
<p>By default, the program is run as the user if invoked
from a client program such as <b class=
"APPLICATION">lpr</b>, <b class="APPLICATION">lpc</b>,
etc. If invoked from <b class="APPLICATION">lpd</b>, it
is run as the user ID specified by the <tt class=
"LITERAL">:user</tt> (default <tt class=
"LITERAL">daemon</tt>) configuration entry.</p>
</li>
<li>
<p>The <tt class="LITERAL">filter_path</tt> (default <tt
class="LITERAL">/bin:/usr/bin:/usr/local/bin</tt>, and
<tt class="LITERAL">filter_ld_path</tt> (default <tt
class="LITERAL">/lib:/usr/lib:/usr/local/lib</tt>,
configuration options specifies the value of the <tt
class="LITERAL">PATH</tt> and <tt class=
"LITERAL">LD_LIBRARY_PATH</tt> environment variables.</p>
</li>
<li>
<p>The <tt class="LITERAL">filter_path</tt> (default <tt
class="LITERAL">/bin:/usr/bin:/usr/local/bin</tt>, and
<tt class="LITERAL">filter_ld_path</tt> (default <tt
class="LITERAL">/lib:/usr/lib:/usr/local/lib</tt>,
configuration option specifies the value of the <tt
class="LITERAL">PATH</tt> and <tt class=
"LITERAL">LD_LIBRARY_PATH</tt> environment variables. The
other enviroment variables are described in <a href=
"filteroptions.htm#FILTERENV"><b class=
"APPLICATION">LPRng</b> ftp mirror sites Filter
Environment Variables</a></p>
</li>
<li>
<p><span class="ACRONYM">ROOT</span> Flag. If the ROOT
flag is specified the filter is executed with Userid and
Effective Userid ROOT (User ID 0). By default it is
executed with the <tt class="LITERAL">user</tt> and <tt
class="LITERAL">group</tt> configuration option user and
group ids. Running a filter as ROOT is extremely
dangerous, and should only be used for programs that
require root permissions to open files or make network
connections from privileged ports.</p>
</li>
<li>
<p><tt class="LITERAL">$-</tt> or <tt class=
"LITERAL">-$</tt> Flag. This flag suppresses appending
options to the filter command line. If the <i class=
"EMPHASIS">$-</i> or <tt class="LITERAL">-$</tt> flag is
not present, the <tt class="LITERAL">:filter_options</tt>
or <tt class="LITERAL">:of_filter_options</tt> for the
<tt class="OPTION">:of</tt> filter values are appended to
the filter command line. If the <tt class=
"LITERAL">:bkf</tt> (Berkeley <b class=
"APPLICATION">lpd</b> filter compatible flag) is <tt
class="LITERAL">TRUE</tt> then the <tt class=
"LITERAL">:bk_filter_options</tt> and <tt class=
"LITERAL">:bk_of_filter_options</tt> values are used
instead of the <tt class="LITERAL">:filter_options</tt>
and <tt class="LITERAL">:of_filter_options</tt>
values.</p>
<div class="TABLE">
<a name="PRINTFILTERCOMMAND"></a>
<p><b>Table 16-1. Print Filter Command Line
Options</b></p>
<table border="1" class="CALSTABLE">
<thead>
<tr>
<th align="LEFT" valign="TOP">Option</th>
<th align="LEFT" valign="TOP">DefaultValue</th>
</tr>
</thead>
<tbody>
<tr>
<td align="LEFT" valign="TOP">Option</td>
<td align="LEFT" valign="TOP">DefaultValue</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">filter_options</tt></td>
<td align="LEFT" valign="TOP">$C $F $H $J $L $P
$Q $R $Z $a $c $d $e $f $h $i $j $k $l $n $p$r $s
$w $x $y $-a</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">of_filter_options</tt></td>
<td align="LEFT" valign="TOP">(same as <tt class=
"LITERAL">filter_options</tt>)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">bk_filter_options</tt></td>
<td align="LEFT" valign="TOP">$P $w $l $x $y $F
$c $L $i $J $C $0n $0h $-a</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">bk_of_filter_options</tt></td>
<td align="LEFT" valign="TOP">$w $l $x $y</td>
</tr>
</tbody>
</table>
</div>
</li>
<li>
<p>By default, for programs that are not being invoked as
print job file filters, the <tt class=
"LITERAL">filter_options</tt> arguments are added. For
print job filters, if the <tt class="LITERAL">:bkf</tt>
flag is set, then the <tt class=
"LITERAL">bk_filter_options</tt> and <tt class=
"LITERAL">bk_of_filter_options</tt> entries are used. The
default <tt class="LITERAL">bk</tt> filter options are
the same as originally used with the BSD <b class=
"APPLICATION">lpr</b> filters. For the <tt class=
"LITERAL">:of</tt> filter, either the <tt class=
"LITERAL">of_filter_options</tt> or <tt class=
"LITERAL">bk_of_filter_options</tt> arguments will be
added.</p>
</li>
<li>
<p>The program arguments will then be scanned and
interpreted. Arguments of the form <tt class=
"LITERAL">$</tt><tt class="LITERAL">letter</tt> will be
translated into values from the print job control file
and/or printcap entry. The letters have the following
meaning:</p>
<div class="TABLE">
<a name="FILTEROPTIONFLAGS"></a>
<p><b>Table 16-2. Filter Command Line Options and
Values</b></p>
<table border="1" class="CALSTABLE">
<thead>
<tr>
<th align="LEFT" valign="TOP">Option</th>
<th align="LEFT" valign="TOP">Purpose or
Value</th>
</tr>
</thead>
<tbody>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">a</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">af</tt> (accounting file name)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">b</tt> </td>
<td align="LEFT" valign="TOP">job size (in K
bytes)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">c</tt> </td>
<td align="LEFT" valign="TOP">binary file (<tt
class="LITERAL">l</tt> format for print
file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">d</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">cd</tt> or <tt class="LITERAL">sd</tt>
entry</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">e</tt> </td>
<td align="LEFT" valign="TOP">print job data file
name (currently being processed)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">f</tt> </td>
<td align="LEFT" valign="TOP">print job original
name when spooled for printing (N info from
control file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">h</tt> </td>
<td align="LEFT" valign="TOP">print job
originating host (H info from control file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">i</tt> </td>
<td align="LEFT" valign="TOP">indent request (I
info from control file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">j</tt> </td>
<td align="LEFT" valign="TOP">job number in spool
queue</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">k</tt> </td>
<td align="LEFT" valign="TOP">print job control
file name</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">l</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">pl</tt> (page length)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">m</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">co</tt></td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">n</tt> </td>
<td align="LEFT" valign="TOP">user name (L info
from control file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">p</tt> </td>
<td align="LEFT" valign="TOP">remote printer
(when processing for bounce queue)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">r</tt> </td>
<td align="LEFT" valign="TOP">remote host (when
processing for bounce queue)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">s</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">sf</tt> (status file)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">t</tt> </td>
<td align="LEFT" valign="TOP">time in common UNIX
format</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">w</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">pw</tt> (page width)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">x</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">px</tt> (page x dimension)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">y</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">py</tt> (page y dimension)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">F</tt> </td>
<td align="LEFT" valign="TOP">print file
format</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">P</tt> </td>
<td align="LEFT" valign="TOP">printer name</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">S</tt> </td>
<td align="LEFT" valign="TOP">printcap <tt class=
"LITERAL">cm</tt> (comment field)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP">Capital letter</td>
<td align="LEFT" valign="TOP">Corresponding line
from control file</td>
</tr>
<tr>
<td align="LEFT" valign="TOP">{key}</td>
<td align="LEFT" valign="TOP">printcap value for
<tt class="LITERAL">key</tt></td>
</tr>
</tbody>
</table>
</div>
<br>
<br>
</li>
<li>
<p>If there is no value for the specified argument, then
the argument is removed from the list. If there is a
value, the actual form of the substitution is controlled
by additional flags as follows.</p>
<div class="TABLE">
<a name="AEN8153"></a>
<p><b>Table 16-3. Filter Command Line Option
Format</b></p>
<table border="1" class="CALSTABLE">
<thead>
<tr>
<th align="LEFT" valign="TOP">Form</th>
<th align="LEFT" valign="TOP">
TranslatedValue</th>
</tr>
</thead>
<tbody>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">$x</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">'-x</tt><tt class=
"REPLACEABLE"><i>value</i></tt><tt class=
"LITERAL">'</tt></td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">$-x</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">'</tt><tt class=
"REPLACEABLE"><i>value</i></tt><tt class=
"LITERAL">'</tt></td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">$0x</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">-x '</tt><tt class=
"REPLACEABLE"><i>value</i></tt><tt class=
"LITERAL">'</tt></td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">$'x</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">-x</tt> <tt class=
"REPLACEABLE"><i>value</i></tt></td>
</tr>
</tbody>
</table>
</div>
<br>
<br>
<p>Each entry in quotes is treated as a single value, as
in /bin/sh. The <tt class="LITERAL">$'x</tt> does not
quote the value. Combinations of the various flags are
allowed. For example, <tt class="LITERAL">$-x</tt> would
simply substitute the value for <tt class=
"LITERAL">x</tt>, and then pass the whitespace separated
components as individual arguments. This last form is
useful for adding in additional flags on the command
line.</p>
</li>
<li>
<p>The command line is parsed, metacharacters are
ruthlessly stripped from all arguments and pathnames and
replaced by <tt class="LITERAL">_</tt> (underscores), and
an argument list suitable for the <tt class=
"LITERAL">execve</tt> system call is formed.</p>
</li>
<li>
<p>A sanitized environment is set up for the program
execution, with the following environment variables.</p>
<div class="TABLE">
<a name="FILTERENV"></a>
<p><b>Table 16-4. Filter Environment Variables</b></p>
<table border="1" class="CALSTABLE">
<thead>
<tr>
<th align="LEFT" valign="TOP">Variable Name</th>
<th align="LEFT" valign="TOP">Meaning</th>
</tr>
</thead>
<tbody>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">CONTROL</tt> </td>
<td align="LEFT" valign="TOP">control file
name</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">DATAFILES</tt> </td>
<td align="LEFT" valign="TOP">list of data file
names</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">HOME</tt> </td>
<td align="LEFT" valign="TOP">Home directory
(client only)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">IFS</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">" \t"</tt></td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">LD_LIBRARY_PATH</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">:filter_ld_path</tt> configuration
information</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">LOGDIR</tt> </td>
<td align="LEFT" valign="TOP">Home directory
(client only)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">LOGNAME</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">L</tt> control file line</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">PATH</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">filter_path</tt> configuration
information</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">PRINTCAP_ENTRY</tt> </td>
<td align="LEFT" valign="TOP">printcap
information</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">SHELL</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"OPTION">:sh</tt> configuration information
(default <tt class="FILENAME">/bin/sh</tt>)</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">SPOOL_DIR</tt> </td>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">:sd</tt> printcap information</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">TZ</tt> </td>
<td align="LEFT" valign="TOP">Time zone</td>
</tr>
<tr>
<td align="LEFT" valign="TOP"><tt class=
"LITERAL">USER</tt> </td>
<td align="LEFT" valign="TOP">User name (client
only)</td>
</tr>
</tbody>
</table>
</div>
<br>
<br>
</li>
<li>
<p>If the filter is to be run by a client program such as
<b class="APPLICATION">lpr</b>, then the environment
variables specified by the <tt class=
"LITERAL">pass_env</tt> configuration or printcap option
will be extracted from the environment, have any
metacharacters removed, and then placed in the
environment variable list. Commonly, the <span class=
"ACRONYM">PGPPASS</span>, <span class=
"ACRONYM">PGPPASSFD</span>, and <span class=
"ACRONYM">PGPPATH</span> are specified.</p>
</li>
<li>
<p>The program is started, with <span class=
"ACRONYM">STDIN</span>, <span class=
"ACRONYM">STDOUT</span>, and <span class=
"ACRONYM">STDERR</span> attached to the appropriate files
or file descriptors. If none is specified, then they are
attached to <tt class="FILENAME">/dev/null</tt>.</p>
</li>
</ol>
<br>
<br>
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