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<h2>16.4 How to pass command lines longer than 126 characters</h2>

<p><em><strong>Q</strong>: Can I invoke my program with a command line longer than the
infamous DOS 126-character limit?</em>

<br><p>
<p><em><strong>Q</strong>: I have a Makefile of Unix origin which contains some
<strong>very</strong> long command lines.  Will it work with DJGPP?</em>

<br><p>
<p><strong>A</strong>:  Yes and yes.  DJGPP supports several methods of passing
command-line arguments which allow it to work around the DOS 126-character
limit.  These are:

<ul>
<li>The <code>!proxy</code> method.  If you invoke the program from within another
DJGPP program (like Make or Gcc compilation driver), it gets the address
of the memory block where the actual command line is stored.  The start-up
code will detect this and use that info to retrieve the command-line
arguments.

<p>This method is suitable only for invoking DJGPP programs from other DJGPP
programs.  You don't have to do anything special to use this method, it is
all done automagically for you by the library functions from the
<code>spawnXX</code> and <code>execXX</code> family on the parent program side, and
by the start-up code on the child side<a rel=footnote href="faq25.html"><sup>27</sup></a>.

</p><li>The environment method.  This is the same as the <code>!proxy</code> method
above, but the information about the long command line is stored in an
environment variable called "<tt> !proxy</tt>" (with the leading blank
and in lower-case).  The reason for two similar, but different methods
is that command-line arguments passed by <code>system</code> library functions
should be globbed by the child, while the arguments passed by
<code>spawnXX</code> and <code>execXX</code> family of functions should not; thus
the former uses the environment method while the latter use the
<code>!proxy</code> method.

<p>This method is used only by the <code>system</code> library function, and only
when the command line is longer than the DOS 126-character limit.

</p><li>The response file method.  Any argument which starts with a <code>@</code>
character (like in <code>myprog @<var>file</var></code>) will cause the named
<var>file</var> to be read and its contents to be used as command-line
arguments, like in many DOS-based compilers and linkers.  If you invoke
your DJGPP program from the DOS command line, this would be the only
method available for you to pass long command lines (like when calling
<code>Gawk</code> or <small>SED</small> without the <code>-f</code> option).

<p>This method is not used by the DJGPP library functions, but you can use
it explicitly in your application code.  It is designed for invoking
non-DJGPP programs that support response files.

<p>Note that this method makes <code>@</code> special when it is the first (or the
only) character of a command-line argument, which should be
protected with quotes if you want to use it verbatim (see <a href="faq16_3.html">how to pass the <b>@</b> character</a>). 
</ul>

<p>Of course, if the DJGPP start-up code doesn't see any of the above
methods, it will use the DOS command line by default.

<p>Since the long command lines are a very important feature, DJGPP's
version of the <code>system</code> library function avoids calling the DOS
command processor, <code>COMMAND.COM</code>, unless it needs to run a batch
file or an internal command of <code>COMMAND.COM</code>.  Other features of
the command processor, like redirection and pipes, are emulated
internally by <code>system</code>.  See the library reference for
<code>system</code>, for more details about its extended functionality.

<p><hr>
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