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| 13 | <A HREF="LPRng-HOWTO.html#toc13">Contents</A> |
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| 14 | <HR> |
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| 15 | <H2><A NAME="secfilter"></A> <A NAME="s13">13. Filters</A></H2> |
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| 16 | |
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| 17 | <P>This section gives an overview of how LPRng uses filter programs, |
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| 18 | and gives a detailed discussion of how the printcap options and |
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| 19 | filters interact. |
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| 20 | <H2><A NAME="ss13.1">13.1 What are filters?</A> |
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| 21 | </H2> |
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| 22 | |
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| 23 | <P>Print filters are one of the most powerful tools in BSD-style printer |
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| 24 | systems. |
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| 25 | <P>In general UNIX terms, a <EM>filter</EM> is a program that takes its input |
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| 26 | file(s), does something with it, and sends the result to its standard |
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| 27 | output. Most UNIX utilities are designed as filters. |
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| 28 | (But since you are a system manager, you should already know that :)) |
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| 29 | <P>In the context of a BSD-style print spooler (and also LPRng), the term |
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| 30 | <EM>filter</EM> refers to a program that processes file while it is |
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| 31 | being transferred to a printer. |
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| 32 | <P>The filter is executed with STDIN reading from the file to be |
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| 33 | printed |
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| 34 | STDOUT to the printer device or a temporary file. |
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| 35 | STDERR (file handle 2) is redirected to the status file, |
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| 36 | and file handle 3 to an accounting file or program. |
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| 37 | <P>A filter can be as simple as a <CODE>LF</CODE> to <CODE>CR/LF</CODE> |
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| 38 | translator, |
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| 39 | or it can incorporate a complete |
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| 40 | accounting system, automatic file type translations, |
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| 41 | or even redirect the job to another printing system. |
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| 42 | <P>As part of the LPRng project, |
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| 43 | the following filters are supported. |
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| 44 | The are many others available for use, |
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| 45 | but are currently not supported. |
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| 46 | <UL> |
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| 47 | <LI> |
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| 48 | <A HREF="#lpf">lpf</A> |
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| 49 | a very simple CR/LF or passthrough filter.</LI> |
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| 50 | <LI> |
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| 51 | <A HREF="#ifhp">ifhp</A> |
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| 52 | HP PCL and PJL printer filters </LI> |
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| 53 | <LI></LI> |
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| 54 | </UL> |
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| 55 | |
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| 56 | The supported filters and other facilities are available from |
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| 57 | <A HREF="ftp://ftp.astart.com/pub/LPRng">ftp://ftp.astart.com/pub/LPRng</A><H2><A NAME="if"></A> <A NAME="ss13.2">13.2 What are print formats?</A> |
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| 58 | </H2> |
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| 59 | |
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| 60 | <P>Options used: |
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| 61 | <UL> |
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| 62 | <LI><CODE>if</CODE>, |
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| 63 | <CODE>cf</CODE>, |
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| 64 | <CODE>df</CODE>, |
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| 65 | <CODE>gf</CODE>, |
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| 66 | <CODE>nf</CODE>, |
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| 67 | <CODE>of</CODE>, |
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| 68 | <CODE>rf</CODE>, |
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| 69 | <CODE>tf</CODE>, |
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| 70 | <CODE>vf</CODE>, |
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| 71 | <EM>X</EM><CODE>f</CODE>, |
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| 72 | <EM> Filter programs </EM></LI> |
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| 73 | </UL> |
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| 74 | <P>LPRng has inherited a set of so-called `<B>print formats</B>' from its |
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| 75 | BSD ancestor. |
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| 76 | The format was used to specify the type of file that was being printed. |
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| 77 | The <CODE>lpd</CODE> server |
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| 78 | used the print format to select the filter for processing the file. |
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| 79 | The de<B>f</B>ault format is <CODE>f</CODE>. |
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| 80 | <P>The user can specify the format (i.e., the file type) by giving |
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| 81 | the appropriate option to <CODE>lpr</CODE>: |
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| 82 | <P> |
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| 83 | <UL> |
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| 84 | <LI><CODE>-b</CODE> or <CODE>-l</CODE>: Binary (literal) file. No processing should |
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| 85 | be done. |
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| 86 | The |
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| 87 | <CODE>l</CODE> format is recorded as the file format.</LI> |
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| 88 | <LI><CODE>-c</CODE>: cifplot(1) output.</LI> |
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| 89 | <LI><CODE>-d</CODE>: TeX DVI file.</LI> |
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| 90 | <LI><CODE>-g</CODE>: Output from the plot(3X) routines.</LI> |
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| 91 | <LI><CODE>-n</CODE> or <CODE>-t</CODE>: (di)troff output.</LI> |
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| 92 | <LI><CODE>-p</CODE>: Text file that should be pre-processed by the <CODE>pr</CODE> |
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| 93 | command, and then by the standard text filter.</LI> |
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| 94 | <LI><CODE>-v</CODE>: Benson Varian raster image.</LI> |
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| 95 | </UL> |
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| 96 | <P>Alternatively, one can also use |
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| 97 | <CODE>-Fx</CODE>, where <CODE>x</CODE> is the format specifier. |
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| 98 | (E.g., <CODE>-Fc</CODE> |
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| 99 | instead of <CODE>-c</CODE>.) |
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| 100 | This last form also allows you to use other |
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| 101 | (non-standard) format specifiers. |
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| 102 | <P>The filter for format |
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| 103 | <CODE>X</CODE> |
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| 104 | is the value for the |
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| 105 | <CODE>Xf</CODE> printcap |
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| 106 | option, |
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| 107 | with some minor exceptions. |
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| 108 | The following |
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| 109 | <CODE>Xf</CODE> |
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| 110 | options have a pre-defined meaning. |
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| 111 | <P> |
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| 112 | <UL> |
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| 113 | <LI><CODE>if</CODE> |
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| 114 | The <CODE>f</CODE> |
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| 115 | format filter, |
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| 116 | i.e. - for the default |
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| 117 | <CODE>f</CODE> |
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| 118 | format. |
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| 119 | All print jobs are passed |
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| 120 | through this one, unless another format is selected.</LI> |
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| 121 | <LI> |
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| 122 | <A NAME="cf"></A> |
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| 123 | <CODE>cf</CODE> Cifplot data filter (for <CODE>-c</CODE> format).</LI> |
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| 124 | <LI> |
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| 125 | <A NAME="df"></A> |
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| 126 | <CODE>df</CODE> Filter for DVI files (<CODE>-d</CODE>).</LI> |
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| 127 | <LI> |
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| 128 | <A NAME="gf"></A> |
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| 129 | <CODE>gf</CODE> Graph data filter (<CODE>-g</CODE>).</LI> |
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| 130 | <LI> |
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| 131 | <A NAME="nf"></A> |
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| 132 | <CODE>nf</CODE> Ditroff data filter (<CODE>-n</CODE>).</LI> |
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| 133 | <LI><CODE>of</CODE> This filter is used for processing the (optional) |
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| 134 | banner at the start and/or end of the print job, |
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| 135 | and also for the interjob separators. |
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| 136 | See |
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| 137 | <A HREF="#ofdetails">of</A> filter for details.</LI> |
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| 138 | <LI> |
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| 139 | <A NAME="rf"></A> |
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| 140 | <CODE>rf</CODE> Filter for Fortran style files (<CODE>-r</CODE>).</LI> |
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| 141 | <LI> |
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| 142 | <A NAME="tf"></A> |
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| 143 | <CODE>tf</CODE> Troff filter (<CODE>-t</CODE>).</LI> |
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| 144 | <LI> |
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| 145 | <A NAME="vf"></A> |
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| 146 | <CODE>vf</CODE> (Versatek) raster image filter (<CODE>-v</CODE>).</LI> |
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| 147 | </UL> |
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| 148 | |
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| 149 | <A NAME="ofdetails"></A> <H2><A NAME="ss13.3">13.3 OF Filter</A> |
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| 150 | </H2> |
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| 151 | |
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| 152 | <P>The |
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| 153 | <CODE>of</CODE> |
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| 154 | filter is used to process banners and job separators. |
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| 155 | The |
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| 156 | <CODE>of</CODE> filter is responsible for performing appropriate |
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| 157 | processing of this information and sending to the printer |
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| 158 | for action. |
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| 159 | <P>While the various file filters are invoked on a once per print file basis, |
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| 160 | the |
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| 161 | <CODE>of</CODE> |
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| 162 | filter is invoked on a once per print job basis. |
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| 163 | <P>This filter is the first one to be started, |
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| 164 | and should perform whatever specialized device initialization |
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| 165 | is needed. |
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| 166 | It should also do whatever accounting procedure is desired |
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| 167 | for start of job accounting. |
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| 168 | <P>The |
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| 169 | <CODE>of</CODE> |
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| 170 | filter will be given any banner printing or job separation |
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| 171 | information for a job. |
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| 172 | As part of its operation, |
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| 173 | it can detect a specific string, |
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| 174 | corresponding to a banner print request, |
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| 175 | and generate a banner. |
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| 176 | (See the |
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| 177 | <A HREF="LPRng-HOWTO-12.html#jobsteps">Job Processing Steps and Printcap Options</A> |
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| 178 | for details.) |
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| 179 | <P>During operation, |
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| 180 | the |
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| 181 | <CODE>lpd</CODE> server will send the special |
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| 182 | <B>stop</B> sequence of <CODE>\031\001</CODE> to the |
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| 183 | <CODE>of</CODE> filter. |
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| 184 | The filter must then suspend itself using a |
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| 185 | <CODE>kill -STOP</CODE> operation. |
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| 186 | The <CODE>lpd</CODE> server will detect that the |
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| 187 | <CODE>of</CODE> filter has suspended itself and then |
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| 188 | will perform other printing operations. |
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| 189 | <P>After the other printing operations have been completed, |
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| 190 | the <CODE>of</CODE> will then be sent a |
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| 191 | <CODE>kill -CONT</CODE> signal. |
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| 192 | <P>This sequence will continue until all information has been printed, |
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| 193 | and then the <CODE>of</CODE> filter's STDIN will be closed. |
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| 194 | The filter will then perform whatever cleanup operations are needed, |
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| 195 | update accounting or other information, |
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| 196 | and exit. |
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| 197 | <H2><A NAME="pr"></A> <A NAME="ss13.4">13.4 LPR -p format</A> |
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| 198 | </H2> |
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| 199 | |
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| 200 | <P>Options used: |
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| 201 | <UL> |
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| 202 | <LI><CODE>pr=</CODE><EM>pr program for p format</EM></LI> |
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| 203 | </UL> |
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| 204 | <P>The <CODE>-p</CODE> format is requires filtering the |
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| 205 | the input files by the <CODE>pr</CODE> utility |
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| 206 | and then passing the result through the |
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| 207 | <CODE>if</CODE> filter. |
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| 208 | <P>This is widely regarded as a kludge and may not be supported |
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| 209 | on your print spooler. |
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| 210 | <H2><A NAME="ss13.5">13.5 LPR binary (-l) format</A> |
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| 211 | </H2> |
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| 212 | |
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| 213 | <P>The binary (or literal) format is <CODE>-l</CODE>. |
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| 214 | The <CODE>if</CODE> filter |
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| 215 | is used to process the file, |
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| 216 | and is invoked with the |
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| 217 | <CODE>-c</CODE> |
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| 218 | (<CODE>c</CODE>ancel processing?) flag. |
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| 219 | <P>The filter will not modify the file when sending it to the printer, |
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| 220 | but may apply various setups to the printer. |
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| 221 | <H2><A NAME="filtercmd"></A> <A NAME="py"></A> <A NAME="px"></A> <A NAME="pw"></A> <A NAME="pl"></A> <A NAME="passenv"></A> <A NAME="filterpath"></A> <A NAME="filterldpath"></A> <A NAME="offilteroptions"></A> <A NAME="filteroptions"></A> <A NAME="bkf"></A> <A NAME="bkoffilteroptions"></A> <A NAME="bkfilteroptions"></A> <A NAME="ss13.6">13.6 Filter Command Line Flags</A> |
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| 222 | </H2> |
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| 223 | |
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| 224 | <P>Options used: |
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| 225 | <UL> |
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| 226 | <LI> <CODE>bk_filter_options=</CODE><EM>Backwards Compatible Filter options</EM></LI> |
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| 227 | <LI> <CODE>bk_of_filter_options=</CODE><EM>Backwards Compatible OF Filter options</EM></LI> |
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| 228 | <LI> <CODE>bkf</CODE><EM> Backwards Compatible Filters</EM></LI> |
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| 229 | <LI> <CODE>filter_ld_path=</CODE><EM>Filter LD_LIBRARY_PATH environment</EM></LI> |
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| 230 | <LI> <CODE>filter_options=</CODE><EM>Filter options</EM></LI> |
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| 231 | <LI> <CODE>filter_path=</CODE><EM>Filter PATH environment</EM></LI> |
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| 232 | <LI> <CODE>of_filter_options=</CODE><EM>OF Filter options</EM></LI> |
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| 233 | <LI> <CODE>pass_env=</CODE><EM>Environment variables to copy to Filter environment</EM></LI> |
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| 234 | <LI> <CODE>pl#</CODE><EM>line count for page</EM></LI> |
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| 235 | <LI> <CODE>pw#</CODE><EM>column count for page</EM></LI> |
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| 236 | <LI> <CODE>px#</CODE><EM>pixel width for page</EM></LI> |
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| 237 | <LI> <CODE>py#</CODE><EM>pixel length for page</EM></LI> |
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| 238 | </UL> |
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| 239 | <P>A filter (or program) specification in the LPRng printcap database |
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| 240 | usually has the form: |
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| 241 | <BLOCKQUOTE><CODE> |
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| 242 | <PRE> |
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| 243 | :option=| [flags] /path [argument | "argument" | 'argument' ]* |
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| 244 | :option=[flags] /path [argument | "argument" | 'argument' ]* |
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| 245 | </PRE> |
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| 246 | </CODE></BLOCKQUOTE> |
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| 247 | <P>The first case is used where the option value can be a string or filter, |
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| 248 | and the second where a program is always expected. |
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| 249 | The following procedure is used to run a filter program. |
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| 250 | Arguments in single or double quotes are passed as a single value, |
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| 251 | as for a shell. |
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| 252 | No escape (backslash) support is provided. |
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| 253 | <P>The sequence of operations to run a filter is as follows: |
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| 254 | <OL> |
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| 255 | <LI>The program must be specified with an absolute path name.</LI> |
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| 256 | <LI>By default, the program is run as the user if invoked from a client |
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| 257 | program such as <CODE>lpr</CODE>, <CODE>lpc</CODE>, etc. |
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| 258 | If invoked from <CODE>lpd</CODE>, it is run as the |
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| 259 | <CODE>server_user</CODE> |
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| 260 | user |
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| 261 | (default <CODE>daemon</CODE>) configuration entry.</LI> |
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| 262 | <LI>The |
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| 263 | <EM>flags</EM> control how the program is to be run. |
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| 264 | The following flags are supported: |
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| 265 | <UL> |
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| 266 | <LI><B>ROOT</B> |
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| 267 | This opens a horrible security loophole, |
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| 268 | as it will run the program as ROOT. |
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| 269 | To enable this option, |
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| 270 | you must set various compilation flags, |
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| 271 | and perform other arcane operations. |
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| 272 | This is deliberately done to make administrators |
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| 273 | read the warnings and admonitions. |
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| 274 | <P>The alternative to ROOT is to have a setuid ROOT executable. |
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| 275 | Under NO circumstances should you run a shell script setuid ROOT, |
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| 276 | with general execute permissions on it. |
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| 277 | </LI> |
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| 278 | <LI><B>-$</B> |
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| 279 | This very odd looking flag is used to suppress the addition of |
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| 280 | additional command line arguments |
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| 281 | specified by the value of <CODE>filter_options</CODE> |
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| 282 | to the program command line.</LI> |
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| 283 | </UL> |
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| 284 | </LI> |
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| 285 | <LI>If the <B>-$</B> flag is not specified, |
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| 286 | the arguments determined by the value of the <CODE>bkf</CODE> |
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| 287 | (Berkeley LPD filter compatible flag) flag are added to the |
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| 288 | filter command line. |
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| 289 | If <CODE>bkf</CODE> is false the |
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| 290 | <CODE>filter_options</CODE> are added for OF filters and |
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| 291 | <CODE>of_filter_options</CODE> |
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| 292 | are added for non-OF filters; |
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| 293 | if it is true, then the |
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| 294 | <CODE>bk_filter_options</CODE> and <CODE>bk_of_filter_options</CODE> are added for |
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| 295 | OF and non-OF filters respectively. |
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| 296 | <P> |
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| 297 | <CENTER><TABLE BORDER><TR><TD> |
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| 298 | <BR> |
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| 299 | Option</TD><TD>DefaultValue</TD></TR><TR><TD> |
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| 300 | <CODE>filter_options</CODE></TD><TD>$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 $-a</TD></TR><TR><TD> |
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| 301 | <CODE>of_filter_options</CODE></TD><TD>(same as <CODE>filter_options</CODE>)</TD></TR><TR><TD> |
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| 302 | <CODE>bk_filter_options</CODE></TD><TD>$P $w $l $x $y $F $c $L $i $J $C $0n $0h $-a</TD></TR><TR><TD> |
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| 303 | <CODE>bk_of_filter_options</CODE></TD><TD>$w $l $x $y</TD></TR><TR><TD> |
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| 304 | |
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| 305 | </TD></TR></TABLE></CENTER> |
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| 306 | <P> |
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| 307 | </LI> |
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| 308 | <LI>By default, |
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| 309 | for programs that are not being invoked as print job file filters, |
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| 310 | the |
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| 311 | <CODE>filter_options</CODE> |
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| 312 | arguments are added. |
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| 313 | For print job filters, if the <CODE>bkf</CODE> flag is set, |
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| 314 | then the |
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| 315 | <CODE>bk_filter_options</CODE> |
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| 316 | and |
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| 317 | <CODE>bk_of_filter_options</CODE> |
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| 318 | entries are used. |
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| 319 | The default <CODE>bk</CODE> filter options are the same as originally used |
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| 320 | with the BSD LPR filters. |
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| 321 | For the <CODE>of</CODE> filter, |
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| 322 | either the <CODE>of_filter_options</CODE> |
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| 323 | or <CODE>bk_of_filter_options</CODE> arguments will be added.</LI> |
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| 324 | <LI>The program arguments will then be scanned and interpreted. |
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| 325 | Arguments of the form <CODE>$</CODE><EM>letter</EM> will be |
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| 326 | translated into values from the |
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| 327 | print job control file and/or printcap entry. |
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| 328 | The letters have the following meaning: |
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| 329 | <CENTER><TABLE BORDER><TR><TD> |
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| 330 | <BR> |
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| 331 | Letter</TD><TD>TranslatedValue</TD></TR><TR><TD> |
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| 332 | <CODE>a </CODE></TD><TD>printcap <CODE>af</CODE> (accounting file name)</TD></TR><TR><TD> |
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| 333 | <CODE>b </CODE></TD><TD>job size (in K bytes)</TD></TR><TR><TD> |
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| 334 | <CODE>c </CODE></TD><TD>binary file (<CODE>l</CODE> format for print file)</TD></TR><TR><TD> |
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| 335 | <CODE>d </CODE></TD><TD>printcap <CODE>cd</CODE> or <CODE>sd</CODE> entry</TD></TR><TR><TD> |
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| 336 | <CODE>e </CODE></TD><TD>print job data file name (currently being processed)</TD></TR><TR><TD> |
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| 337 | <CODE>f </CODE></TD><TD>print job original name when spooled for printing (N info from control file)</TD></TR><TR><TD> |
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| 338 | <CODE>h </CODE></TD><TD>print job originating host (H info from control file)</TD></TR><TR><TD> |
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| 339 | <CODE>i </CODE></TD><TD>indent request (I info from control file)</TD></TR><TR><TD> |
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| 340 | <CODE>j </CODE></TD><TD>job number in spool queue</TD></TR><TR><TD> |
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| 341 | <CODE>k </CODE></TD><TD>print job control file name</TD></TR><TR><TD> |
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| 342 | <CODE>l </CODE></TD><TD>printcap <CODE>pl</CODE> (page length)</TD></TR><TR><TD> |
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| 343 | <CODE>m </CODE></TD><TD>printcap <CODE>co</CODE></TD></TR><TR><TD> |
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| 344 | <CODE>n </CODE></TD><TD>user name (L info from control file)</TD></TR><TR><TD> |
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| 345 | <CODE>p </CODE></TD><TD>remote printer (when processing for bounce queue)</TD></TR><TR><TD> |
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| 346 | <CODE>r </CODE></TD><TD>remote host (when processing for bounce queue)</TD></TR><TR><TD> |
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| 347 | <CODE>s </CODE></TD><TD>printcap <CODE>sf</CODE> (status file)</TD></TR><TR><TD> |
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| 348 | <CODE>t </CODE></TD><TD>time in common UNIX format</TD></TR><TR><TD> |
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| 349 | <CODE>w </CODE></TD><TD>printcap <CODE>pw</CODE> (page width)</TD></TR><TR><TD> |
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| 350 | <CODE>x </CODE></TD><TD>printcap <CODE>px</CODE> (page x dimension)</TD></TR><TR><TD> |
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| 351 | <CODE>y </CODE></TD><TD>printcap <CODE>py</CODE> (page y dimension)</TD></TR><TR><TD> |
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| 352 | <CODE>F </CODE></TD><TD>print file format</TD></TR><TR><TD> |
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| 353 | <CODE>P </CODE></TD><TD>printer name</TD></TR><TR><TD> |
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| 354 | <CODE>S </CODE></TD><TD>printcap <CODE>cm</CODE> (comment field)</TD></TR><TR><TD> |
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| 355 | Capital letter</TD><TD>Corresponding line from control file</TD></TR><TR><TD> |
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| 356 | {key}</TD><TD>printcap value for <CODE>key</CODE></TD></TR><TR><TD> |
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| 357 | |
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| 358 | </TD></TR></TABLE></CENTER> |
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| 359 | </LI> |
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| 360 | <LI>If there is no value for the specified argument, |
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| 361 | then the argument is removed from the list. |
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| 362 | If there is a value, the actual form of the substitution is |
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| 363 | controlled by additional flags as follows. |
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| 364 | <CENTER><TABLE BORDER><TR><TD> |
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| 365 | <BR> |
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| 366 | Form</TD><TD>TranslatedValue</TD></TR><TR><TD> |
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| 367 | <CODE> $x </CODE></TD><TD><CODE>'-x<EM>value</EM>' </CODE></TD></TR><TR><TD> |
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| 368 | <CODE> $-x </CODE></TD><TD><CODE> '<EM>value</EM>' </CODE></TD></TR><TR><TD> |
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| 369 | <CODE> $0x </CODE></TD><TD><CODE> -x '<EM>value</EM>' </CODE></TD></TR><TR><TD> |
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| 370 | <CODE> $'x </CODE></TD><TD><CODE> -x <EM>value</EM> </CODE></TD></TR><TR><TD> |
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| 371 | |
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| 372 | </TD></TR></TABLE></CENTER> |
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| 373 | |
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| 374 | <P>Each entry in quotes is treated as a single value, |
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| 375 | as in /bin/sh. |
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| 376 | The <CODE>$'x</CODE> does not quote the value. |
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| 377 | Combinations of the various flags are allowed. For example, |
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| 378 | <CODE>$-x</CODE> would simply substitute the value for <CODE>x</CODE>, |
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| 379 | and then pass the whitespace separated components as individual arguments. |
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| 380 | This last form is useful for adding in additional flags on the command line. |
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| 381 | </LI> |
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| 382 | <LI>The command line is parsed, |
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| 383 | metacharacters are ruthlessly stripped from all arguments and pathnames |
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| 384 | and replaced by <CODE>_</CODE> (underscores), |
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| 385 | and an argument list suitable for the <CODE>execve</CODE> system call |
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| 386 | is formed.</LI> |
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| 387 | <LI>A sanitized environment is set up for the program execution, |
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| 388 | with the following environment variables. |
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| 389 | <P> |
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| 390 | <CENTER><TABLE BORDER><TR><TD> |
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| 391 | <BR> |
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| 392 | <CODE> USER </CODE></TD><TD>User name (client only)</TD></TR><TR><TD> |
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| 393 | <CODE> LOGNAME </CODE></TD><TD>L control file info</TD></TR><TR><TD> |
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| 394 | <CODE> HOME </CODE></TD><TD>Home directory (client only)</TD></TR><TR><TD> |
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| 395 | <CODE> LOGDIR </CODE></TD><TD>Home directory (client only)</TD></TR><TR><TD> |
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| 396 | <CODE> PATH </CODE></TD><TD><CODE>filter_path</CODE> configuration information</TD></TR><TR><TD> |
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| 397 | <CODE> LD_LIBRARY_PATH </CODE></TD><TD><CODE> filter_ld_path </CODE> configuration information</TD></TR><TR><TD> |
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| 398 | <CODE> SHELL </CODE></TD><TD><CODE>/bin/sh</CODE></TD></TR><TR><TD> |
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| 399 | <CODE> IFS </CODE></TD><TD><CODE>" \t"</CODE></TD></TR><TR><TD> |
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| 400 | <CODE> TZ </CODE></TD><TD>Time zone</TD></TR><TR><TD> |
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| 401 | <CODE> SPOOL_DIR </CODE></TD><TD><CODE>sd</CODE> printcap info</TD></TR><TR><TD> |
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| 402 | <CODE> CONTROL_DIR </CODE></TD><TD><CODE>cd</CODE> printcap info</TD></TR><TR><TD> |
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| 403 | <CODE> PRINTCAP_ENTRY </CODE></TD><TD>printcap info</TD></TR><TR><TD> |
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| 404 | <CODE> CONTROL </CODE></TD><TD>control file</TD></TR><TR><TD> |
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| 405 | |
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| 406 | </TD></TR></TABLE></CENTER> |
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| 407 | <P> |
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| 408 | </LI> |
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| 409 | <LI>If the filter is to be run by a client program such as <CODE>lpr</CODE>, |
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| 410 | then the environment variables specified by the |
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| 411 | <CODE>pass_env</CODE> configuration or printcap option will be |
|---|
| 412 | extracted from the environment, |
|---|
| 413 | have any metacharacters removed, |
|---|
| 414 | and then placed in the environment variable list. |
|---|
| 415 | Commonly, the |
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| 416 | <CODE>PGPPASS</CODE>, |
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| 417 | <CODE>PGPPASSFD</CODE>, |
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| 418 | and <CODE>PGPPATH</CODE> are specified.</LI> |
|---|
| 419 | <LI>The program is started, |
|---|
| 420 | with STDIN, STDOUT, and STDERR attached to the appropriate files or |
|---|
| 421 | file descriptors. |
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| 422 | If none is specified, then they are attached to |
|---|
| 423 | <CODE>/dev/null</CODE>.</LI> |
|---|
| 424 | </OL> |
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| 425 | <H2><A NAME="ss13.7">13.7 LPRng Supported Filters</A> |
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| 426 | </H2> |
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| 427 | |
|---|
| 428 | <P>There already exists a large library of ready-to-use filters. Some of |
|---|
| 429 | them have LPRng-specific versions, which can be found at the |
|---|
| 430 | <A HREF="LPRng-HOWTO-1.html#secftp">LPRng ftp mirror sites</A>. |
|---|
| 431 | <H3>Filter Distribution Conventions</H3> |
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| 432 | |
|---|
| 433 | <P>By convention, |
|---|
| 434 | most filters are either totally standalone (very rare), |
|---|
| 435 | or require a set of support files. |
|---|
| 436 | There are two types of support files: per print queue configuration information |
|---|
| 437 | and global support information. |
|---|
| 438 | <P>Since a print filter will execute with the current directory set to the |
|---|
| 439 | spool queue directory, |
|---|
| 440 | most filters expect that per print queue configuration information |
|---|
| 441 | should be kept in the spool directory. |
|---|
| 442 | Most <EM>vintage</EM> filters insist on having these files <EM>hidden</EM> |
|---|
| 443 | with names such as <B><CODE>.setup</CODE></B>. |
|---|
| 444 | This can make it difficult for administrators to determine where the |
|---|
| 445 | configuration files are. |
|---|
| 446 | <P>It is strongly recommended that filters and information |
|---|
| 447 | be placed in commonly accessible directories such as |
|---|
| 448 | <CODE><B>/usr/local/libexec/filters</B></CODE>, |
|---|
| 449 | and the executables in subdirectories. |
|---|
| 450 | This allows the LPRng administrator to set the privileges on these |
|---|
| 451 | directories such that only the <CODE>lpd</CODE> process can |
|---|
| 452 | access them. |
|---|
| 453 | <P>Most of the LPRng supported filters can either be used as a |
|---|
| 454 | <CODE>if</CODE> or <CODE>of</CODE> filter. |
|---|
| 455 | The filter will examine the format type passed by the <CODE>-F<EM>X</EM></CODE> |
|---|
| 456 | command line argument, |
|---|
| 457 | and if it is <CODE>o</CODE> it will perform as an <CODE>of</CODE> filter. |
|---|
| 458 | <P>Alternatively, |
|---|
| 459 | the filter will check the filename in the pathname by which is was invoked. |
|---|
| 460 | If the name has the substring <CODE>of</CODE> in the filename, |
|---|
| 461 | then it assumes it is to act as an <CODE>of</CODE> filter. |
|---|
| 462 | This allows symbolic links to be made to a common filter executable, |
|---|
| 463 | each of which corresponds to the filter name by which it is to be invoked. |
|---|
| 464 | <P>When a filter is invoked, |
|---|
| 465 | it is passed a large number of options, |
|---|
| 466 | many of which are totally ignored in filter operation. |
|---|
| 467 | However, |
|---|
| 468 | for many purposes it is necessary to provide options to the |
|---|
| 469 | filters to tailor their operation to the particular spool queue needs. |
|---|
| 470 | <P>By convention, |
|---|
| 471 | all LPRng supported filters use the |
|---|
| 472 | <BLOCKQUOTE><CODE> |
|---|
| 473 | <PRE> |
|---|
| 474 | -Tkey=value[,key=value] |
|---|
| 475 | </PRE> |
|---|
| 476 | </CODE></BLOCKQUOTE> |
|---|
| 477 | <P>convention for specifying filter configuration option values. |
|---|
| 478 | <H2><A NAME="lpf"></A> <A NAME="ss13.8">13.8 lpf</A> |
|---|
| 479 | </H2> |
|---|
| 480 | |
|---|
| 481 | <P>Source code: |
|---|
| 482 | <A HREF="LPRng-HOWTO-1.html#secftp">LPRng Distribution</A><P>This filter is distributed as part of the LPRng source code, |
|---|
| 483 | and has a very limited functionality. |
|---|
| 484 | By default, |
|---|
| 485 | it only translates <CODE>\n</CODE> to <CODE>\r\n</CODE> |
|---|
| 486 | sequences, |
|---|
| 487 | and detects the OF Filter Stop sequence when invoked as an OF filter. |
|---|
| 488 | <UL> |
|---|
| 489 | <LI>Options:<BR> |
|---|
| 490 | <CODE>-Tcrlf</CODE> - suppress <CODE>\n</CODE> to <CODE>\r\n</CODE> translation</LI> |
|---|
| 491 | </UL> |
|---|
| 492 | <H2><A NAME="ifhp"></A> <A NAME="ss13.9">13.9 IFHP Filter</A> |
|---|
| 493 | </H2> |
|---|
| 494 | |
|---|
| 495 | <P>Source code: |
|---|
| 496 | <A HREF="LPRng-HOWTO-1.html#secftp">LPRng Distribution, ifhp-<em>version</em>.tgz</A><P>This filter supports a wide variety of <I>smart</I> printers, |
|---|
| 497 | or to be more specific, |
|---|
| 498 | printers which support PostScript, PCL or PJL languages. |
|---|
| 499 | <P>As explained in |
|---|
| 500 | <A HREF="LPRng-HOWTO-3.html#installref">Setting Up Your Printer</A>, |
|---|
| 501 | you can have a parallel (unidirectional), |
|---|
| 502 | serial (bidirectional), |
|---|
| 503 | or network (bidirectional) connection. |
|---|
| 504 | When using a bidirectional connection, |
|---|
| 505 | you can sometime obtain or gratuitously receive error and/or status |
|---|
| 506 | information from the printer. |
|---|
| 507 | <P>Some printers will spontaneously generate error messages when printing |
|---|
| 508 | a job on a bidirectional interface. |
|---|
| 509 | Usually, though, |
|---|
| 510 | it it necessary to force the printer to provide status in a reasonable format. |
|---|
| 511 | <P>Some printers have the capability of printing either PCL or PostScript; |
|---|
| 512 | some require special setup commands and some will <EM>autosense</EM> which |
|---|
| 513 | type of job is being printed. |
|---|
| 514 | <P>If you are printing text, |
|---|
| 515 | and not using a Page Description Language like PostScript or PCL, |
|---|
| 516 | then you may want to download a font to the printer. |
|---|
| 517 | This is especially the case when you are trying to print text files |
|---|
| 518 | in a non-English font. |
|---|
| 519 | <P>Some printers will provide a <EM>hardware</EM> page counter value when requested; |
|---|
| 520 | however, |
|---|
| 521 | the means of requesting differ from model to model. |
|---|
| 522 | <P>Sometimes you want to generate a special banner for a particular printer, |
|---|
| 523 | and need to put in some dynamic information. |
|---|
| 524 | While this can be done by the <CODE>lpd</CODE> server using the |
|---|
| 525 | <CODE>bp</CODE> program specification, |
|---|
| 526 | it turns out that non-LPRng systems which want to use the <CODE>ifhp</CODE> |
|---|
| 527 | want to have the same facilities. |
|---|
| 528 | Thus, you need to have some way to get the same effect as the <CODE>bp</CODE> |
|---|
| 529 | option, but at the filter level. |
|---|
| 530 | <P>Having done <CODE>lpd</CODE> banner generation and printing, |
|---|
| 531 | why not have the filter run an accounting script as well? |
|---|
| 532 | <P>At this point, I suspect that the reader is beginning to suspect that |
|---|
| 533 | making a general purpose filter to support all of these possibilities is |
|---|
| 534 | difficult. |
|---|
| 535 | That is incorrect. It is <B>extremely</B> difficult. |
|---|
| 536 | <P>However, |
|---|
| 537 | the <CODE>ifhp</CODE> filter greatly simplifies this, |
|---|
| 538 | as it uses a simple database together with some printer configuration options. |
|---|
| 539 | For details, |
|---|
| 540 | see the <CODE>ifhp</CODE> documentation for details on using the filter. |
|---|
| 541 | For the terminally impatient, |
|---|
| 542 | the following is a quick cookbook: |
|---|
| 543 | <BLOCKQUOTE><CODE> |
|---|
| 544 | <PRE> |
|---|
| 545 | # network connection to jet direct box, |
|---|
| 546 | # no banners, HP compatible |
|---|
| 547 | lp |
|---|
| 548 | :lp=ipaddr%9100 |
|---|
| 549 | :/usr/local/libexec/filters/ifhp |
|---|
| 550 | :sh:sf |
|---|
| 551 | # |
|---|
| 552 | # banner added |
|---|
| 553 | # |
|---|
| 554 | lp |
|---|
| 555 | :bp=/usr/local/libexec/filters/pclbanner |
|---|
| 556 | :of=/usr/local/libexec/filters/ifhp |
|---|
| 557 | :if=/usr/local/libexec/filters/ifhp |
|---|
| 558 | :sf |
|---|
| 559 | # |
|---|
| 560 | # for a parallel port printer or when you want VERY fast |
|---|
| 561 | # throughput, no pagecounts, error messages, etc. The |
|---|
| 562 | # |
|---|
| 563 | lp |
|---|
| 564 | :ifhp=status@ |
|---|
| 565 | :/usr/local/libexec/filters/ifhp |
|---|
| 566 | :sh:sf |
|---|
| 567 | </PRE> |
|---|
| 568 | </CODE></BLOCKQUOTE> |
|---|
| 569 | <H2><A NAME="ss13.10">13.10 Using your own filters</A> |
|---|
| 570 | </H2> |
|---|
| 571 | |
|---|
| 572 | <P>If you already have a working setup, with its own specific filter |
|---|
| 573 | programs, you might want to keep them. Or, you might want to write a |
|---|
| 574 | set of your own. |
|---|
| 575 | <P>See the source code in the |
|---|
| 576 | <A HREF="LPRng-HOWTO-1.html#secftp">LPRng Distribution, FILTERS_LPRng-<version>.tgz</A> files for examples. |
|---|
| 577 | <HR> |
|---|
| 578 | <A HREF="LPRng-HOWTO-14.html">Next</A> |
|---|
| 579 | <A HREF="LPRng-HOWTO-12.html">Previous</A> |
|---|
| 580 | <A HREF="LPRng-HOWTO.html#toc13">Contents</A> |
|---|
| 581 | </BODY> |
|---|
| 582 | </HTML> |
|---|
