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<h4 class="subsection">2.6.1 Input Data Structure</h4>

<p>The data structure that is used as the argument to the parameter mode
application incorporates all the information about the command line and
<a name="index-environment-202"></a><a name="index-command-line-203"></a>the environment variables. It is in the form of a triple
<code>((</code><var>files</var><code>,</code><var>options</var><code>),</code><var>environs</var><code>)</code>. The fields have
these interpretations.

     <dl>
<dt><var>files</var><dd>is a list of quadruples
<code>((</code><var>date</var><code>,</code><var>path</var><code>),(</code><var>preamble</var><code>,</code><var>contents</var><code>))</code>, with
one quadruple for each input file named on the command line (but not the
virtual code file or the <code>avram</code> executable).  The list will be in
the same order as the filenames on the command line, and is not affected
by options interspersed with them. The fields in each item have the
following interpretations.

          <dl>
<dt><var>date</var><dd>is the time stamp of the file in as a character string in the usual
<a name="index-time-stamp-204"></a><a name="index-date-205"></a><a name="index-system-time-206"></a><a name="index-current-time-207"></a><a name="index-Unix-208"></a>Unix format, for example, <code>Fri Jan 19 14:34:44 GMT 2001</code>. If the
file corresponds to standard input, the current system time and date are
used. 
<br><dt><var>path</var><dd>is the full path of the file, expressed as a list of strings. If the
<a name="index-file-names-209"></a><a name="index-paths-210"></a><a name="index-absolute-path-211"></a><a name="index-relative-path-212"></a>file corresponds to standard input, the list is empty. Otherwise, the
first string in the list is the file name. The next is the name of the
file's parent directory, if any. The next is the parent of the parent,
and so on. The root directory is indicated by the empty string, so that
any path ending with the empty string is an absolute path, while any path
ending with a non-empty string is relative to the current working
directory.  Path separators (i.e., slashes) are omitted. 
<br><dt><var>preamble</var><dd>In the case of a text file, or any file not conforming to the format in
<a name="index-preamble-213"></a><a href="File-Format.html#File-Format">File Format</a>, this field is <code>nil</code>. Otherwise, this field contains
the preamble of the file expressed as a list of strings, or contains
just the empty string if the file has no preamble. Any leading hashes in
the preamble of the file are stripped. 
<br><dt><var>contents</var><dd>In the case of a text file (as indicated by the <var>preamble</var> field), this
<a name="index-text-files-214"></a>field will contain a list of character strings, with each line of the file
contained in a character string. Otherwise, it can contain data in any
format, which are obtained by converting the data section of the file
to a tree. 
</dl>
     <br><dt><var>options</var><dd>is a list of quadruples of the form
<code>((</code><var>position</var><code>,</code><var>longform</var><code>),(</code><var>keyword</var><code>,</code><var>params</var><code>))</code>
with one quadruple for each option appearing on the command line after
the name of the virtual code file.

          <dl>
<dt><var>position</var><dd>is a natural number indicating the position of the option on the command
<a name="index-naturals-215"></a><a name="index-command-line-216"></a>line. The position numbers of all the options will form an ascending
sequence, but not necessarily consecutive nor starting with zero.  The
missing numbers in the sequence will correspond to the positions of the
file names on the command line, allowing their positions to be inferred by
applications for which the position matters. 
<br><dt><var>longform</var><dd>is a boolean value which is true if the option starts with two or more
<a name="index-booleans-217"></a>dashes but false otherwise. 
<br><dt><var>keyword</var><dd>is the key word of the option expressed as a character string. For example
in the case of a command line option <kbd>--foo=bar,baz</kbd>, the keyword is
<code>foo</code>. Leading dashes are stripped. 
<br><dt><var>params</var><dd>is a list of character strings identifying the parameters for the
command line option in question. In the case of an option of the form
<kbd>--foo=bar,baz</kbd>, the first character string in the list will be
<code>bar</code> and the next will be <code>baz</code>. The same applies if the
option is written <kbd>--foo bar,baz</kbd> or <kbd>--foo =bar,baz</kbd>. If there
are no parameters associated with the option, the list is empty. 
</dl>
     <br><dt><var>environs</var><dd>is a list of pairs of character strings, with one pair in the list for
<a name="index-environment-218"></a>each environment variable. The identifier is the left string in the
pair, and the value is the right.  For example, if the environment
contains the definition <code>OSTYPE=linux-gnu</code>, there will be a pair in
the list whose left side is the string <code>OSTYPE</code> and whose
right side is the string <code>linux-gnu</code>. 
</dl>

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