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<title>avram - a virtual machine code interpreter: 1.2.1 Filter Mode</title>

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<a name="Filter-Mode"></a>
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<hr size="1">
<a name="Filter-Mode-1"></a>
<h3 class="subsection">1.2.1 Filter Mode</h3>

<a name="index-filter-mode"></a>
<a name="index-modes-2"></a>
<p>In filter mode, the argument to the function given by the virtual code
is taken from standard input, and the result is written to standard
output, except for error messages resulting from a failure to evaluate
the function, which are written to standard error.
See section <a href="Diagnostics.html#Diagnostics">Diagnostics</a>. Filter mode is indicated whenever these three
conditions are all met.
</p>
<ul>
<li>
Either at least one of the filter mode options appears on the command
line preceding the first filename parameter, or there are no options at
all. See section <a href="Filter-Mode-Options.html#Filter-Mode-Options">Filter Mode Options</a>.
</li><li>
Exactly one filename parameter appears on the command line,
which is the name of the virtual machine code file.
</li><li>
Either the filename comes last on the command line, or the
&lsquo;<samp>--unparameterized</samp>&rsquo; option precedes it, causing
everything following it to be ignored.
</li></ul>
 
<p>Examples:
</p>
<dl compact="compact">
<dt> <kbd>avram mynewapp &lt; inputfilename</kbd></dt>
<dd><a name="index-standard-input-1"></a>
<p>In this example, filter mode is recognized by default because there are
no options or input files on the command line to indicate
otherwise. (The input file redirected into standard input is not treated
by the shell as a command line argument.)
</p></dd>
<dt> <kbd>cat somefile | avram -r coolprog &gt; outputfile</kbd></dt>
<dd><p>In this example, the &lsquo;<samp>-r</samp>&rsquo; option gives it away, being one of the
filter mode options, in addition to the fact that there are no input
file parameters or application-specific options.
</p></dd>
<dt> <kbd>avram -u devilmaycare.avm --bogusoption ignoredparameter</kbd></dt>
<dd><p>In this case, filter mode is forced by the &lsquo;<samp>-u</samp>&rsquo;
option despite indications to the contrary.
</p></dd>
</dl>

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