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<h3 class="section">1.5 Input Files</h3>

<p><a name="index-input-29"></a><a name="index-source-program-30"></a><a name="index-files_002c-input-31"></a>We use the phrase <dfn>source program</dfn>, abbreviated <dfn>source</dfn>, to
describe the program input to one run of <samp><span class="command">as</span></samp>.  The program may
be in one or more files; how the source is partitioned into files
doesn't change the meaning of the source.

<!-- I added "con" prefix to "catenation" just to prove I can overcome my -->
<!-- APL training...   doc@cygnus.com -->
   <p>The source program is a concatenation of the text in all the files, in the
order specified.

<!-- man begin DESCRIPTION -->
   <p>Each time you run <samp><span class="command">as</span></samp> it assembles exactly one source
program.  The source program is made up of one or more files. 
(The standard input is also a file.)

   <p>You give <samp><span class="command">as</span></samp> a command line that has zero or more input file
names.  The input files are read (from left file name to right).  A
command line argument (in any position) that has no special meaning
is taken to be an input file name.

   <p>If you give <samp><span class="command">as</span></samp> no file names it attempts to read one input file
from the <samp><span class="command">as</span></samp> standard input, which is normally your terminal.  You
may have to type &lt;ctl-D&gt; to tell <samp><span class="command">as</span></samp> there is no more program
to assemble.

   <p>Use &lsquo;<samp><span class="samp">--</span></samp>&rsquo; if you need to explicitly name the standard input file
in your command line.

   <p>If the source is empty, <samp><span class="command">as</span></samp> produces a small, empty object
file.

<!-- man end -->
<h4 class="subheading">Filenames and Line-numbers</h4>

<p><a name="index-input-file-linenumbers-32"></a><a name="index-line-numbers_002c-in-input-files-33"></a>There are two ways of locating a line in the input file (or files) and
either may be used in reporting error messages.  One way refers to a line
number in a physical file; the other refers to a line number in a
&ldquo;logical&rdquo; file.  See <a href="Errors.html#Errors">Error and Warning Messages</a>.

   <p><dfn>Physical files</dfn> are those files named in the command line given
to <samp><span class="command">as</span></samp>.

   <p><dfn>Logical files</dfn> are simply names declared explicitly by assembler
directives; they bear no relation to physical files.  Logical file names help
error messages reflect the original source file, when <samp><span class="command">as</span></samp> source
is itself synthesized from other files.  <samp><span class="command">as</span></samp> understands the
&lsquo;<samp><span class="samp">#</span></samp>&rsquo; directives emitted by the <code>gcc</code> preprocessor.  See also
<a href="File.html#File"><code>.file</code></a>.

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