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<h4 class="subsection">8.1.3 Generate Message Catalogs files</h4>

<p><a name="index-gencat-807"></a>The <code>gencat</code> program is specified in the X/Open standard and the
GNU implementation follows this specification and so processes
all correctly formed input files.  Additionally some extension are
implemented which help to work in a more reasonable way with the
<code>catgets</code> functions.

   <p>The <code>gencat</code> program can be invoked in two ways:

<pre class="example">     `gencat [<var>Option</var>]... [<var>Output-File</var> [<var>Input-File</var>]...]`
</pre>
   <p>This is the interface defined in the X/Open standard.  If no
<var>Input-File</var> parameter is given input will be read from standard
input.  Multiple input files will be read as if they are concatenated. 
If <var>Output-File</var> is also missing, the output will be written to
standard output.  To provide the interface one is used to from other
programs a second interface is provided.

<pre class="smallexample">     `gencat [<var>Option</var>]... -o <var>Output-File</var> [<var>Input-File</var>]...`
</pre>
   <p>The option &lsquo;<samp><span class="samp">-o</span></samp>&rsquo; is used to specify the output file and all file
arguments are used as input files.

   <p>Beside this one can use <samp><span class="file">-</span></samp> or <samp><span class="file">/dev/stdin</span></samp> for
<var>Input-File</var> to denote the standard input.  Corresponding one can
use <samp><span class="file">-</span></samp> and <samp><span class="file">/dev/stdout</span></samp> for <var>Output-File</var> to denote
standard output.  Using <samp><span class="file">-</span></samp> as a file name is allowed in X/Open
while using the device names is a GNU extension.

   <p>The <code>gencat</code> program works by concatenating all input files and
then <strong>merge</strong> the resulting collection of message sets with a
possibly existing output file.  This is done by removing all messages
with set/message number tuples matching any of the generated messages
from the output file and then adding all the new messages.  To
regenerate a catalog file while ignoring the old contents therefore
requires to remove the output file if it exists.  If the output is
written to standard output no merging takes place.

<p class="noindent">The following table shows the options understood by the <code>gencat</code>
program.  The X/Open standard does not specify any option for the
program so all of these are GNU extensions.

     <dl>
<dt>&lsquo;<samp><span class="samp">-V</span></samp>&rsquo;<dt>&lsquo;<samp><span class="samp">--version</span></samp>&rsquo;<dd>Print the version information and exit. 
<br><dt>&lsquo;<samp><span class="samp">-h</span></samp>&rsquo;<dt>&lsquo;<samp><span class="samp">--help</span></samp>&rsquo;<dd>Print a usage message listing all available options, then exit successfully. 
<br><dt>&lsquo;<samp><span class="samp">--new</span></samp>&rsquo;<dd>Do never merge the new messages from the input files with the old content
of the output files.  The old content of the output file is discarded. 
<br><dt>&lsquo;<samp><span class="samp">-H</span></samp>&rsquo;<dt>&lsquo;<samp><span class="samp">--header=name</span></samp>&rsquo;<dd>This option is used to emit the symbolic names given to sets and
messages in the input files for use in the program.  Details about how
to use this are given in the next section.  The <var>name</var> parameter to
this option specifies the name of the output file.  It will contain a
number of C preprocessor <code>#define</code>s to associate a name with a
number.

     <p>Please note that the generated file only contains the symbols from the
input files.  If the output is merged with the previous content of the
output file the possibly existing symbols from the file(s) which
generated the old output files are not in the generated header file. 
</dl>

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