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          <div>
            <h1 class="title"><a id="_programming"/>Capítulo 12. Programación</h1>
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      <div class="toc">
        <p>
          <strong>Tabla de contenidos</strong>
        </p>
        <dl class="toc">
          <dt>
            <span class="section">
              <a href="ch12.es.html#_the_shell_script">12.1. Los archivos de órdenes</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_posix_shell_compatibility">12.1.1. Compatibilidad del intérprete de órdenes POSIX</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_shell_parameters">12.1.2. Parámetros del intérprete de órdenes</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_shell_conditionals">12.1.3. Condiciones del intérprete de órdenes</a>
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              <dt>
                <span class="section">
                  <a href="ch12.es.html#_shell_loops">12.1.4. Shell loops</a>
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                <span class="section">
                  <a href="ch12.es.html#_the_shell_command_line_processing_sequence">12.1.5. The shell command-line processing sequence</a>
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                  <a href="ch12.es.html#_utility_programs_for_shell_script">12.1.6. Utility programs for shell script</a>
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                  <a href="ch12.es.html#_shell_script_example_with_zenity">12.1.8. Shell script example with zenity</a>
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            <span class="section">
              <a href="ch12.es.html#_make">12.2. Make</a>
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            <span class="section">
              <a href="ch12.es.html#_c">12.3. C</a>
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                <span class="section">
                  <a href="ch12.es.html#_simple_c_program_gcc">12.3.1. Programa sencillo en C (gcc)</a>
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            <span class="section">
              <a href="ch12.es.html#_debug">12.4. Depuración</a>
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            <dl>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_basic_gdb_execution">12.4.1. Fundamentos de gdb</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_debugging_the_debian_package">12.4.2. Depurando un paquete Debian</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_obtaining_backtrace">12.4.3. Obtaining backtrace</a>
                </span>
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              <dt>
                <span class="section">
                  <a href="ch12.es.html#_advanced_gdb_commands">12.4.4. Advanced gdb commands</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_debugging_x_errors">12.4.5. Debugging X Errors</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_check_dependency_on_libraries">12.4.6. Check dependency on libraries</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_memory_leak_detection_tools">12.4.7. Memory leak detection tools</a>
                </span>
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                <span class="section">
                  <a href="ch12.es.html#_static_code_analysis_tools">12.4.8. Static code analysis tools</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_disassemble_binary">12.4.9. Disassemble binary</a>
                </span>
              </dt>
            </dl>
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          <dt>
            <span class="section">
              <a href="ch12.es.html#_flex_a_better_lex">12.5. Flex — a better Lex</a>
            </span>
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          <dt>
            <span class="section">
              <a href="ch12.es.html#_bison_a_better_yacc">12.6. Bison — a better Yacc</a>
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              <a href="ch12.es.html#_autoconf">12.7. Autoconf</a>
            </span>
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          <dd>
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              <dt>
                <span class="section">
                  <a href="ch12.es.html#_compile_and_install_a_program">12.7.1. Compile and install a program</a>
                </span>
              </dt>
              <dt>
                <span class="section">
                  <a href="ch12.es.html#_uninstall_program">12.7.2. Uninstall program</a>
                </span>
              </dt>
            </dl>
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          <dt>
            <span class="section">
              <a href="ch12.es.html#_perl_short_script_madness">12.8. Perl short script madness</a>
            </span>
          </dt>
          <dt>
            <span class="section">
              <a href="ch12.es.html#_web">12.9. Web</a>
            </span>
          </dt>
          <dt>
            <span class="section">
              <a href="ch12.es.html#_the_source_code_translation">12.10. The source code translation</a>
            </span>
          </dt>
          <dt>
            <span class="section">
              <a href="ch12.es.html#_making_debian_package">12.11. Making Debian package</a>
            </span>
          </dt>
        </dl>
      </div>
      <p>Algunos consejos para quién quiera aprender a programar en el sistema Debian
para trazar el código fuente. Aquí están los paquetes más importantes y los
paquetes de documentación más importantes para la programación.</p>
      <div class="table">
        <a id="listofpackagestohelpprograming"/>
        <p class="title">
          <strong>Tabla 12.1. Lista de paquetes que ayudan a la programación</strong>
        </p>
        <div class="table-contents">
          <table class="table" summary="Lista de paquetes que ayudan a la programación" border="1">
            <colgroup>
              <col style="text-align: left"/>
              <col style="text-align: left"/>
              <col style="text-align: left"/>
              <col style="text-align: left"/>
            </colgroup>
            <thead>
              <tr>
                <th style="text-align: left">
    paquete
    </th>
                <th style="text-align: left">
    popularidad
    </th>
                <th style="text-align: left">
    tamaño
    </th>
                <th style="text-align: left">
    documentación
    </th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/autoconf">
<code class="literal">autoconf</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=autoconf">V:29, I:226</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/a/autoconf.html">1868</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info autoconf</code>" proporcionado con
<code class="literal">autoconf-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/automake">
<code class="literal">automake</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=automake">V:27, I:220</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/a/automake.html">1707</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info automake</code>" proporcionado con
<code class="literal">automake1.10-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/bash"> <code class="literal">bash</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=bash">V:853, I:999</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/b/bash.html">5799</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info bash</code>" proporcionado con <code class="literal">bash-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/bison"> <code class="literal">bison</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=bison">V:10, I:113</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/b/bison.html">2061</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info bison</code>" proporcionado con
<code class="literal">bison-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/cpp"> <code class="literal">cpp</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=cpp">V:394, I:806</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/c/cpp.html">41</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info cpp</code>" proporcionado con <code class="literal">cpp-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/ddd"> <code class="literal">ddd</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=ddd">V:1, I:13</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/d/ddd.html">3965</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info ddd</code>" proporcionado por <code class="literal">ddd-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/exuberant-ctags">
<code class="literal">exuberant-ctags</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=exuberant-ctags">V:7, I:38</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/e/exuberant-ctags.html">333</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">exuberant-ctags</span>(1)</span>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/flex"> <code class="literal">flex</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=flex">V:10, I:101</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/f/flex.html">1174</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info flex</code>" proporcionado por <code class="literal">flex-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/gawk"> <code class="literal">gawk</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=gawk">V:355, I:478</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/gawk.html">2199</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info gawk</code>" proporcionado por <code class="literal">gawk-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/gcc"> <code class="literal">gcc</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=gcc">V:148, I:606</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/gcc.html">43</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info gcc</code>" proporcionado por <code class="literal">gcc-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/gdb"> <code class="literal">gdb</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=gdb">V:21, I:140</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/gdb.html">7983</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info gdb</code>" proporcionado por <code class="literal">gdb-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/gettext">
<code class="literal">gettext</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=gettext">V:53, I:367</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/gettext.html">7076</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info gettext</code>" proporcionado por
<code class="literal">gettext-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/gfortran">
<code class="literal">gfortran</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=gfortran">V:20, I:63</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/gfortran.html">16</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info gfortran</code>" proporcionado por
<code class="literal">gfortran-doc</code> (Fortran 95)
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/fpc"> <code class="literal">fpc</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=fpc">I:4</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/f/fpc.html">113</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">fpc</span>(1)</span>
y html por <code class="literal">fp-docs</code> (Pascal)
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/glade"> <code class="literal">glade</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=glade">V:1, I:12</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/g/glade.html">2209</a>
                </td>
                <td style="text-align: left">
    proporciona ayuda por medio del menú (Constructor UI)
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/libc6"> <code class="literal">libc6</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=libc6">V:933, I:999</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/libc/libc6.html">10679</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info libc</code>" proporcionado por
<code class="literal">glibc-doc</code> y <code class="literal">glibc-doc-reference</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/make"> <code class="literal">make</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=make">V:154, I:622</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/m/make.html">1211</a>
                </td>
                <td style="text-align: left">
    "<code class="literal">info make</code>" proporcionado por <code class="literal">make-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/xutils-dev">
<code class="literal">xutils-dev</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=xutils-dev">V:2, I:18</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/x/xutils-dev.html">1466</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">imake</span>(1)</span>,
<span class="citerefentry"><span class="refentrytitle">xmkmf</span>(1)</span>,
etc.
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/mawk"> <code class="literal">mawk</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=mawk">V:371, I:997</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/m/mawk.html">183</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">mawk</span>(1)</span>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/perl"> <code class="literal">perl</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=perl">V:610, I:996</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/p/perl.html">651</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">perl</span>(1)</span>
y páginas html proporcionadas por <code class="literal">perl-doc</code> y
<code class="literal">perl-doc-html</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/python">
<code class="literal">python</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=python">V:683, I:988</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/p/python.html">648</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">python</span>(1)</span>
y páginas html proporcionado por <code class="literal">python-doc</code></td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/tcl8.4">
<code class="literal">tcl8.4</code> </a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=tcl8.4">V:3, I:50</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/t/tcl8.4.html">NOT_FOUND</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">tcl</span>(3)</span>
y páginas de manual detalladas proporcionadas por
<code class="literal">tcl8.4-doc</code></td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/tk8.4"> <code class="literal">tk8.4</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=tk8.4">V:1, I:31</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/t/tk8.4.html">NOT_FOUND</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">tk</span>(3)</span>
y páginas de manual detalladas proporcionados por
<code class="literal">tk8.4-doc</code></td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/ruby"> <code class="literal">ruby</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=ruby">V:103, I:321</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/r/ruby.html">38</a>
                </td>
                <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">ruby</span>(1)</span>
y la referencia interactiva proporcionada por <code class="literal">ri</code></td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/vim"> <code class="literal">vim</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=vim">V:118, I:393</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/v/vim.html">2374</a>
                </td>
                <td style="text-align: left">
    ayuda(F1) del menú proporacionado por <code class="literal">vim-doc</code>
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/susv2"> <code class="literal">susv2</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=susv2">I:0</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/s/susv2.html">15</a>
                </td>
                <td style="text-align: left">
    cumple "<a class="ulink" href="http://www.unix.org/version2/">La Especificación Única
de UNIX v2</a>"
    </td>
              </tr>
              <tr>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.debian.org/sid/susv3"> <code class="literal">susv3</code>
</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://qa.debian.org/popcon.php?package=susv3">I:0</a>
                </td>
                <td style="text-align: left">
                  <a class="ulink" href="http://packages.qa.debian.org/s/susv3.html">15</a>
                </td>
                <td style="text-align: left">
    cumple "<a class="ulink" href="http://www.unix.org/version3/">La Especificación Única
de UNIX v3</a>"
    </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <br class="table-break"/>
      <p>Las referencia en línea está disponible escribiendo by typing "<code class="literal">man
nombre</code>" tras instalar los paquetes <code class="literal">manpages</code> y
<code class="literal">manpages-dev</code>. La referencia en línea para las
herramientas GNU están disponibles escribiendo "<code class="literal">info
nombre_de_programa</code>" después de instalar los paquetes
correspondientes de documentación. Pude necesitar incluir los repositorios
<code class="literal">contrib</code> y <code class="literal">non-free</code> además del
repositorio <code class="literal">main</code> ya que una parte de la documentación
GFDL no se cosidera que cumple con DFSG.</p>
      <div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
        <table border="0" summary="Warning">
          <tr>
            <td rowspan="2" align="center" valign="top">
              <img alt="[Aviso]" src="images/warning.png"/>
            </td>
            <th align="left">Aviso</th>
          </tr>
          <tr>
            <td align="left" valign="top">
              <p>No use"<code class="literal">test</code>" como nombre de un archivo ejecutable.
"<code class="literal">test</code>" es una órden interna del intérprete de órdenes.</p>
            </td>
          </tr>
        </table>
      </div>
      <div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;">
        <table border="0" summary="Caution">
          <tr>
            <td rowspan="2" align="center" valign="top">
              <img alt="[Atención]" src="images/caution.png"/>
            </td>
            <th align="left">Atención</th>
          </tr>
          <tr>
            <td align="left" valign="top">
              <p>Usted puede instalar programas de software directametne compilado de la
fuente en "<code class="literal">/usr/local</code>" o "<code class="literal">/opt</code>" para
evitar la colisión con los programas del sistema.</p>
            </td>
          </tr>
        </table>
      </div>
      <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
        <table border="0" summary="Tip">
          <tr>
            <td rowspan="2" align="center" valign="top">
              <img alt="[Sugerencia]" src="images/tip.png"/>
            </td>
            <th align="left">Sugerencia</th>
          </tr>
          <tr>
            <td align="left" valign="top">
              <p><a class="ulink" href="http://www.99-bottles-of-beer.net/">Los ejemplos de código para
crear "La canción de 99 botellas de Cerveza"</a> le aportará buenas
ideas para pácticamente cualquier lenguaje de programación.</p>
            </td>
          </tr>
        </table>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_the_shell_script"/>12.1. Los archivos de órdenes</h2>
            </div>
          </div>
        </div>
        <p>Un <a class="ulink" href="http://es.wikipedia.org/wiki/Script_(informática)">archivo de órdenes</a> es un archivo de
texto co el bit de ejecución activado y contiene órdenes con el formato
siguiente.</p>
        <pre class="screen">#!/bin/sh
 ... líneas de órdenes</pre>
        <p>La primera línea determina el intérprete del shell que se encarga de leer y
ejecutar el contenido del archivo.</p>
        <p>La lectura de archivos de órdenes es la <span class="strong"><strong>mejor</strong></span> manera de entender como funciona un sistema
tipo Unix. Aquí, doy algunos apuntes para la programación de archivos de
órdenes. Consulte "Los errores de los archivos de órdenes" (<a class="ulink" href="http://www.greenend.org.uk/rjk/2001/04/shell.html">http://www.greenend.org.uk/rjk/2001/04/shell.html</a>)
para aprender los errores más comunes.</p>
        <p>No como el modo interactivo de la consola (see <a class="xref" href="ch01.es.html#_the_simple_shell_command" title="1.5. Órdenes simples del intérpete de órdenes">Sección 1.5, “Órdenes simples del intérpete de órdenes”</a> and <a class="xref" href="ch01.es.html#_unix_like_text_processing" title="1.6. Procesamiento de texto al estilo Unix">Sección 1.6, “Procesamiento de texto al estilo Unix”</a>) los archivos de órdenes se usan
generalmente parámetros, condiciones e iteraciones.</p>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_posix_shell_compatibility"/>12.1.1. Compatibilidad del intérprete de órdenes POSIX</h3>
              </div>
            </div>
          </div>
          <p>Muchos de los archivos de órdenes pueden ser interpretados por un intérprete
<a class="ulink" href="http://es.wikipedia.org/wiki/POSIX">POSIX</a> (consulte <a class="xref" href="ch01.es.html#list-of-shell-programs" title="Tabla 1.13. Lista de intérpretes de órdenes">Tabla 1.13, “Lista de intérpretes de órdenes”</a>). El intérprete de órdenes del sistema
por defecto es "<code class="literal">/bin/sh</code>" el cual es un enlace simbólico
que referencia al programa actual.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p><span class="citerefentry"><span class="refentrytitle">bash</span>(1)</span>
para <code class="literal">lenny</code> o más antiguo
</p>
              </li>
              <li class="listitem">
                <p><span class="citerefentry"><span class="refentrytitle">dash</span>(1)</span>
para <code class="literal">squeeze</code> o más nuevo
</p>
              </li>
            </ul>
          </div>
          <p>Evite escribir archivos de órdenes con particularidades de  <span class="strong"><strong>bash</strong></span> o <span class="strong"><strong>zs</strong></span> para
hacerlo portable entre intérpretes de órdenes POSIX. Puede comprobaro
utilizando
<span class="citerefentry"><span class="refentrytitle">checkbashisms</span>(1)</span>.</p>
          <div class="table">
            <a id="listoftypicalbashisms"/>
            <p class="title">
              <strong>Tabla 12.2. Enumeración de particularidades de bash</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="Enumeración de particularidades de bash" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    Bien: POSIX
    </th>
                    <th style="text-align: left">
    Mal: bashism
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">if [ "$foo" = "$bar" ] ; then …</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">if [ "$foo" == "$bar" ] ; then …</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">diff -u archivo.c.orig archivo.c</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">diff -u archivo.c{.orig,}</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">mkdir /foobar /foobaz</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">mkdir /foo{bar,baz}</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">funcname() { … }</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">function funcname() { … }</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
    octal format: "<code class="literal">\377</code>"
    </td>
                    <td style="text-align: left">
    formato hexadecimal: "<code class="literal">\xff</code>"
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <p>La órden "<code class="literal">echo</code>" debe utilizarse con cuidado ya que su
implementación cambia entre la órden interna y la externa.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
Evite utilizar cualquier opción excepto <code class="literal">-n</code>".
</p>
              </li>
              <li class="listitem">
                <p>
Evite utilizar secuencias de escape en una cadena ya que su tratamiento
varia.
</p>
              </li>
            </ul>
          </div>
          <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Note">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Nota]" src="images/note.png"/>
                </td>
                <th align="left">Nota</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Ya que la opción "<code class="literal">-n</code>" <span class="strong"><strong>no</strong></span> pertenece realmente a la sintáxis POSIX es
aceptada normalmente.</p>
                </td>
              </tr>
            </table>
          </div>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Utilice la órden "<code class="literal">printf</code>" en vez de la órden
"<code class="literal">echo</code>" si necesita incluir secuencias de caracteres en
las cadenas de caracteres de salida.</p>
                </td>
              </tr>
            </table>
          </div>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_shell_parameters"/>12.1.2. Parámetros del intérprete de órdenes</h3>
              </div>
            </div>
          </div>
          <p>Frecuentemente son utilizados por el intérprete de órdenes parámetros
especiales</p>
          <div class="table">
            <a id="listofshellparameters"/>
            <p class="title">
              <strong>Tabla 12.3. Enumeración de los parámetros de intérprete de órdenes</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="Enumeración de los parámetros de intérprete de órdenes" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    parámetro del intérprete de órdenes
    </th>
                    <th style="text-align: left">
    valor
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$0</code>
                </td>
                    <td style="text-align: left">
    nombre del archivo de órdenes
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$1</code>
                </td>
                    <td style="text-align: left">
    primer argumento del archivo de órdenes
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$9</code>
                </td>
                    <td style="text-align: left">
    noveno argumento del archivo de órdenes
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$#</code>
                </td>
                    <td style="text-align: left">
    parámetro posicionado en el número
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">"$*"</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">"$1 $2 $3 $4 … "</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">"$@"</code>
                </td>
                    <td style="text-align: left">
                  <code class="literal">"$1" "$2" "$3" "$4" …</code>
                </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$?</code>
                </td>
                    <td style="text-align: left">
    estado de finalización de la órden más reciente
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$$</code>
                </td>
                    <td style="text-align: left">
    PID de este archivo de órdenes
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">$!</code>
                </td>
                    <td style="text-align: left">
    PID del trabajo en segundo plano que se ha iniciado más recientemente
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <p>Las<span class="strong"><strong>expansiones de parámetros</strong></span>
fundamentales que debe recordar son las que se muestran.</p>
          <div class="table">
            <a id="listofshellparameterexpansions"/>
            <p class="title">
              <strong>Tabla 12.4. Enumeración de expansiones de parámetros del intérprete de órdenes</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="Enumeración de expansiones de parámetros del intérprete de órdenes" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    forma de expresión del parámetro
    </th>
                    <th style="text-align: left">
    valor si <code class="literal">var</code> esta activado
    </th>
                    <th style="text-align: left">
    valor si <code class="literal">var</code> no está asignado
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var:-string}</code>
                </td>
                    <td style="text-align: left">
    "<code class="literal">$var</code>"
    </td>
                    <td style="text-align: left">
    "<code class="literal">string</code>"
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var:+string}</code>
                </td>
                    <td style="text-align: left">
    "<code class="literal">string</code>"
    </td>
                    <td style="text-align: left">
    "<code class="literal">null</code>"
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var:=string}</code>
                </td>
                    <td style="text-align: left">
    "<code class="literal">$var</code>"
    </td>
                    <td style="text-align: left">
    "<code class="literal">string</code>" (y ejecuta "<code class="literal">var=string</code>")
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var:?string}</code>
                </td>
                    <td style="text-align: left">
    "<code class="literal">$var</code>"
    </td>
                    <td style="text-align: left">
    echo "<code class="literal">string</code>" a <span class="strong"><strong>stderr</strong></span>
(y finalizar con error)
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <p>Aquí, el símbolo "<code class="literal">:</code>" en todos estos operadores es ahora
opcional.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p><span class="strong"><strong>con</strong></span> "<code class="literal">:</code>" el operador =
comprueba que <span class="strong"><strong>existe</strong></span> y <span class="strong"><strong>no es null</strong></span>
</p>
              </li>
              <li class="listitem">
                <p><span class="strong"><strong>sin</strong></span> "<code class="literal">:</code>" el operador =
comprueba unicamente si <span class="strong"><strong>existe</strong></span>
</p>
              </li>
            </ul>
          </div>
          <div class="table">
            <a id="listofkeyshellpatersubstitutions"/>
            <p class="title">
              <strong>Tabla 12.5. Enumeración de las sustituciones clave de parámetros del intérprete de
órdenes</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="Enumeración de las sustituciones clave de parámetros del intérprete de&#10;órdenes" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    formulario de sustitución del parámetro
    </th>
                    <th style="text-align: left">
    resultado
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var%suffix}</code>
                </td>
                    <td style="text-align: left">
    elimina patrón del sufijo más pequeño
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var%%suffix}</code>
                </td>
                    <td style="text-align: left">
    elimina el patrón del sufijo más largo
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var#prefix}</code>
                </td>
                    <td style="text-align: left">
    elimina el patrón del prefijo más pequeño
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">${var##prefix}</code>
                </td>
                    <td style="text-align: left">
    elimina el patrón del prefijo más largo
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_shell_conditionals"/>12.1.3. Condiciones del intérprete de órdenes</h3>
              </div>
            </div>
          </div>
          <p>Cada comando devuelve un <span class="strong"><strong>estado de salida</strong></span>
que puede usarse para expresioneos condicionales.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
Éxito: 0 ("Verdadero")
</p>
              </li>
              <li class="listitem">
                <p>
Error: no 0 ("Falso")
</p>
              </li>
            </ul>
          </div>
          <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Note">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Nota]" src="images/note.png"/>
                </td>
                <th align="left">Nota</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>"0" in the shell conditional context means "True", while "0" in the C
conditional context means "False".</p>
                </td>
              </tr>
            </table>
          </div>
          <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Note">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Nota]" src="images/note.png"/>
                </td>
                <th align="left">Nota</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>"<code class="literal">[</code>" is the equivalent of the <code class="literal">test</code>
command, which evaluates its arguments up to "<code class="literal">]</code>" as a
conditional expression.</p>
                </td>
              </tr>
            </table>
          </div>
          <p>Basic <span class="strong"><strong>conditional idioms</strong></span> to remember are
the following.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
"<code class="literal">&lt;command&gt; &amp;&amp; &lt;if_success_run_this_command_too&gt;
|| true</code>"
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">&lt;command&gt; || &lt;if_not_success_run_this_command_too&gt; ||
true</code>"
</p>
              </li>
              <li class="listitem">
                <p>
A multi-line script snippet as the following
</p>
              </li>
            </ul>
          </div>
          <pre class="screen">if [ &lt;conditional_expression&gt; ]; then
 &lt;if_success_run_this_command&gt;
else
 &lt;if_not_success_run_this_command&gt;
fi</pre>
          <p>Here trailing "<code class="literal">|| true</code>" was needed to ensure this shell
script does not exit at this line accidentally when shell is invoked with
"<code class="literal">-e</code>" flag.</p>
          <div class="table">
            <a id="listoffilecompartionalexpression"/>
            <p class="title">
              <strong>Tabla 12.6. List of file comparison operators in the conditional expression</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of file comparison operators in the conditional expression" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    ecuación
    </th>
                    <th style="text-align: left">
    condition to return logical true
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-e &lt;file&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file&gt; exists
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-d &lt;file&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file&gt; exists and is a directory
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-f &lt;file&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file&gt; exists and is a regular file
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-w &lt;file&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file&gt; exists and is writable
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-x &lt;file&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file&gt; exists and is executable
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;file1&gt; -nt &lt;file2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file1&gt; is newer than &lt;file2&gt; (modification)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;file1&gt; -ot &lt;file2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file1&gt; is older than &lt;file2&gt; (modification)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;file1&gt; -ef &lt;file2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;file1&gt; and &lt;file2&gt; are on the same device and the same inode
number
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <div class="table">
            <a id="listofstringcomptionalexpression"/>
            <p class="title">
              <strong>Tabla 12.7. List of string comparison operators in the conditional expression</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of string comparison operators in the conditional expression" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    ecuación
    </th>
                    <th style="text-align: left">
    condition to return logical true
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-z &lt;str&gt;</code>
                </td>
                    <td style="text-align: left">
    la longitud de &lt;str&gt; es cero
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">-n &lt;str&gt;</code>
                </td>
                    <td style="text-align: left">
    la longitud de &lt;str&gt; no es cero
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;str1&gt; = &lt;str2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;str1&gt; and &lt;str2&gt; are equal
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;str1&gt; != &lt;str2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;str1&gt; y &lt;str2&gt; no son iguales
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;str1&gt; &lt; &lt;str2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;str1&gt; sorts before &lt;str2&gt; (locale dependent)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">&lt;str1&gt; &gt; &lt;str2&gt;</code>
                </td>
                    <td style="text-align: left">
    &lt;str1&gt; sorts after &lt;str2&gt; (locale dependent)
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <p>Los operadores <span class="strong"><strong>aritméticos</strong></span> de comparación
de enteros en la expresión original son "<code class="literal">-eq</code>",
"<code class="literal">-ne</code>", "<code class="literal">-lt</code>",
"<code class="literal">-le</code>", "<code class="literal">-gt</code>" y
"<code class="literal">-ge</code>".</p>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_shell_loops"/>12.1.4. Shell loops</h3>
              </div>
            </div>
          </div>
          <p>There are several loop idioms to use in POSIX shell.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
"<code class="literal">for x in foo1 foo2 … ; do comand0 ; done</code>" asigna
secuencialmente elementos de la lista "<code class="literal">foo1 foo2 …</code>" a la
variable "<code class="literal">x</code>" y ejecuta "<code class="literal">comando</code>".
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">while condición ; do comando ; done</code>" repite
"<code class="literal">comando</code>" mientras "<code class="literal">condición</code>" sea
verdadero.
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">until condición ; do comando ; done</code>" repite
"<code class="literal">comando</code>" mientras "<code class="literal">condición</code>" no sea
verdadero.
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">break</code>" permite salir del bucle.
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">continue</code>" permite continuar con la próxima iteración del
bucle.
</p>
              </li>
            </ul>
          </div>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>The <a class="ulink" href="https://es.wikipedia.org/wiki/C_(lenguaje_de_programación)">C</a>-language like numeric iteration can be
realized by using
<span class="citerefentry"><span class="refentrytitle">seq</span>(1)</span>
as the "<code class="literal">foo1 foo2 …</code>" generator.</p>
                </td>
              </tr>
            </table>
          </div>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Consulta <a class="xref" href="ch09.es.html#_repeating_a_command_looping_over_files" title="9.3.9. Repetición de una órden sobre archivos">Sección 9.3.9, “Repetición de una órden sobre archivos”</a>.</p>
                </td>
              </tr>
            </table>
          </div>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_the_shell_command_line_processing_sequence"/>12.1.5. The shell command-line processing sequence</h3>
              </div>
            </div>
          </div>
          <p>The shell processes a script roughly as the following sequence.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
The shell reads a line.
</p>
              </li>
              <li class="listitem">
                <p>
The shell groups a part of the line as <span class="strong"><strong>one
token</strong></span> if it is within <code class="literal">"…"</code> or
<code class="literal">'…'</code>.
</p>
              </li>
              <li class="listitem">
                <p>
The shell splits other part of a line into <span class="strong"><strong>tokens</strong></span> by the following.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p>
Whitespaces: <code class="literal">&lt;space&gt; &lt;tab&gt; &lt;newline&gt;</code>
</p>
                    </li>
                    <li class="listitem">
                      <p>
Metacharacters: <code class="literal">&lt; &gt; | ; &amp; ( )</code>
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell checks the <span class="strong"><strong>reserved word</strong></span> for
each token to adjust its behavior if not within <code class="literal">"…"</code> or
<code class="literal">'…'</code>.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p><span class="strong"><strong>palabras reservadas</strong></span>: <code class="literal">if then
elif else fi for in while unless do done case esac</code></p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell expands <span class="strong"><strong>alias</strong></span> if not within
<code class="literal">"…"</code> or <code class="literal">'…'</code>.
</p>
              </li>
              <li class="listitem">
                <p>
The shell expands <span class="strong"><strong>tilde</strong></span> if not within
<code class="literal">"…"</code> or <code class="literal">'…'</code>.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p>
"<code class="literal">~</code>" → el directorio home del usuario actual
</p>
                    </li>
                    <li class="listitem">
                      <p>
"<code class="literal">~&lt;usuario&gt;</code>" → el directorio home de
<code class="literal">&lt;usuario&gt;</code>
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell expands <span class="strong"><strong>parameter</strong></span> to its value
if not within <code class="literal">'…'</code>.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p><span class="strong"><strong>parameter</strong></span>:
"<code class="literal">$PARAMETER</code>" or "<code class="literal">${PARAMETER}</code>"
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell expands <span class="strong"><strong>command substitution</strong></span> if
not within <code class="literal">'…'</code>.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p>
"<code class="literal">$( comando )</code>" → la salida de
"<code class="literal">comando</code>"
</p>
                    </li>
                    <li class="listitem">
                      <p>
"<code class="literal">` comando `</code>" → la salida de "<code class="literal">comando</code>"
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell expands <span class="strong"><strong>pathname glob</strong></span> to
matching file names if not within <code class="literal">"…"</code> or
<code class="literal">'…'</code>.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p><code class="literal">*</code> → cualesquier caracteres
</p>
                    </li>
                    <li class="listitem">
                      <p><code class="literal">?</code> → un caracter
</p>
                    </li>
                    <li class="listitem">
                      <p><code class="literal">[…]</code> →  cualquiera de los caracteres en
"<code class="literal"></code>"
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell looks up <span class="strong"><strong>command</strong></span> from the
following and execute it.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p><span class="strong"><strong>function</strong></span> definition
</p>
                    </li>
                    <li class="listitem">
                      <p><span class="strong"><strong>builtin</strong></span> command
</p>
                    </li>
                    <li class="listitem">
                      <p><span class="strong"><strong>executable file</strong></span> in
"<code class="literal">$PATH</code>"
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
The shell goes to the next line and repeats this process again from the top
of this sequence.
</p>
              </li>
            </ul>
          </div>
          <p>Las comillas simples no tienen efecto dentro de comillas dobles.</p>
          <p>Executing "<code class="literal">set -x</code>" in the shell or invoking the shell
with "<code class="literal">-x</code>" option make the shell to print all of commands
executed.  This is quite handy for debugging.</p>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_utility_programs_for_shell_script"/>12.1.6. Utility programs for shell script</h3>
              </div>
            </div>
          </div>
          <p>In order to make your shell program as portable as possible across Debian
systems, it is a good idea to limit utility programs to ones provided by
<span class="strong"><strong>essential</strong></span> packages.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
"<code class="literal">aptitude search ~E</code>" lista paquetes <span class="strong"><strong>esenciales</strong></span>.
</p>
              </li>
              <li class="listitem">
                <p>
"<code class="literal">dpkg -L &lt;paquete&gt; | grep '/man/man.*/'</code>" lista
páginas 'man' para los comandos que ofrece
<code class="literal">&lt;paquete&gt;</code>.
</p>
              </li>
            </ul>
          </div>
          <div class="table">
            <a id="listofpackagescosforshellscripts"/>
            <p class="title">
              <strong>Tabla 12.8. List of packages containing small utility programs for shell scripts</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of packages containing small utility programs for shell scripts" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    paquete
    </th>
                    <th style="text-align: left">
    popularidad
    </th>
                    <th style="text-align: left">
    tamaño
    </th>
                    <th style="text-align: left">
    descripción
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/coreutils">
<code class="literal">coreutils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=coreutils">V:881, I:999</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/c/coreutils.html">15103</a>
                    </td>
                    <td style="text-align: left">
    GNU core utilities
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/debianutils">
<code class="literal">debianutils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=debianutils">V:934, I:999</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/d/debianutils.html">213</a>
                    </td>
                    <td style="text-align: left">
    miscellaneous utilities specific to Debian
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/bsdmainutils">
<code class="literal">bsdmainutils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=bsdmainutils">V:866, I:998</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/b/bsdmainutils.html">566</a>
                    </td>
                    <td style="text-align: left">
    collection of more utilities from FreeBSD
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/bsdutils">
<code class="literal">bsdutils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=bsdutils">V:851, I:999</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/b/bsdutils.html">238</a>
                    </td>
                    <td style="text-align: left">
    basic utilities from 4.4BSD-Lite
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/moreutils">
<code class="literal">moreutils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=moreutils">V:4, I:19</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/m/moreutils.html">201</a>
                    </td>
                    <td style="text-align: left">
    additional Unix utilities
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Although <code class="literal">moreutils</code> may not exist ouside of Debian, it
offers interesting small programs.  Most notable one is
<span class="citerefentry"><span class="refentrytitle">sponge</span>(8)</span>
which is quite useful when you wish to overwrite original file.</p>
                </td>
              </tr>
            </table>
          </div>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_shell_script_dialog"/>12.1.7. Shell script dialog</h3>
              </div>
            </div>
          </div>
          <p>The user interface of a simple shell program can be improved from dull
interaction by <code class="literal">echo</code> and <code class="literal">read</code> commands
to more interactive one by using one of the so-called dialog program etc.</p>
          <div class="table">
            <a id="listofuserinterfaceprograms"/>
            <p class="title">
              <strong>Tabla 12.9. List of user interface programs</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of user interface programs" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    paquete
    </th>
                    <th style="text-align: left">
    popularidad
    </th>
                    <th style="text-align: left">
    tamaño
    </th>
                    <th style="text-align: left">
    descripción
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/x11-utils">
<code class="literal">x11-utils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=x11-utils">V:305, I:635</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/x/x11-utils.html">637</a>
                    </td>
                    <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">xmessage</span>(1)</span>:
display a message or query in a window (X)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/whiptail">
<code class="literal">whiptail</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=whiptail">V:415, I:995</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/w/whiptail.html">68</a>
                    </td>
                    <td style="text-align: left">
    displays user-friendly dialog boxes from shell scripts (newt)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/dialog">
<code class="literal">dialog</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=dialog">V:29, I:151</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/d/dialog.html">1111</a>
                    </td>
                    <td style="text-align: left">
    displays user-friendly dialog boxes from shell scripts (ncurses)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/zenity">
<code class="literal">zenity</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=zenity">V:112, I:425</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/z/zenity.html">362</a>
                    </td>
                    <td style="text-align: left">
    display graphical dialog boxes from shell scripts (gtk2.0)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/ssft"> <code class="literal">ssft</code>
</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=ssft">V:0, I:0</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/s/ssft.html">129</a>
                    </td>
                    <td style="text-align: left">
    Shell Scripts Frontend Tool (wrapper for zenity, kdialog, and dialog with
gettext)
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/gettext">
<code class="literal">gettext</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=gettext">V:53, I:367</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/g/gettext.html">7076</a>
                    </td>
                    <td style="text-align: left">
    "<code class="literal">/usr/bin/gettext.sh</code>": translate message
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_shell_script_example_with_zenity"/>12.1.8. Shell script example with zenity</h3>
              </div>
            </div>
          </div>
          <p>Here is a simple script which creates ISO image with RS02 data supplemented
by
<span class="citerefentry"><span class="refentrytitle">dvdisaster</span>(1)</span>.</p>
          <pre class="screen">#!/bin/sh -e
# gmkrs02 : Copyright (C) 2007 Osamu Aoki &lt;osamu@debian.org&gt;, Public Domain
#set -x
error_exit()
{
  echo "$1" &gt;&amp;2
  exit 1
}
# Initialize variables
DATA_ISO="$HOME/Desktop/iso-$$.img"
LABEL=$(date +%Y%m%d-%H%M%S-%Z)
if [ $# != 0 ] &amp;&amp; [ -d "$1" ]; then
  DATA_SRC="$1"
else
  # Select directory for creating ISO image from folder on desktop
  DATA_SRC=$(zenity --file-selection --directory  \
    --title="Select the directory tree root to create ISO image") \
    || error_exit "Exit on directory selection"
fi
# Check size of archive
xterm -T "Check size $DATA_SRC" -e du -s $DATA_SRC/*
SIZE=$(($(du -s $DATA_SRC | awk '{print $1}')/1024))
if [ $SIZE -le 520 ] ; then
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is good for CD backup:\\n $SIZE MB"
elif [ $SIZE -le 3500 ]; then
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is good for DVD backup :\\n $SIZE MB"
else
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is too big to backup : $SIZE MB"
  error_exit "The data size is too big to backup :\\n $SIZE MB"
fi
# only xterm is sure to have working -e option
# Create raw ISO image
rm -f "$DATA_ISO" || true
xterm -T "genisoimage $DATA_ISO" \
  -e genisoimage -r -J -V "$LABEL" -o "$DATA_ISO" "$DATA_SRC"
# Create RS02 supplemental redundancy
xterm -T "dvdisaster $DATA_ISO" -e  dvdisaster -i "$DATA_ISO" -mRS02 -c
zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
  --text="ISO/RS02 data ($SIZE MB) \\n created at: $DATA_ISO"
# EOF</pre>
          <p>You may wish to create launcher on the desktop with command set something
like "<code class="literal">/usr/local/bin/gmkrs02 %d</code>".</p>
        </div>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_make"/>12.2. Make</h2>
            </div>
          </div>
        </div>
        <p><a class="ulink" href="http://es.wikipedia.org/wiki/Make">Make</a> is a utility to maintain groups of
programs. Upon execution of
<span class="citerefentry"><span class="refentrytitle">make</span>(1)</span>,
<code class="literal">make</code> read the rule file, "<code class="literal">Makefile</code>",
and updates a target if it depends on prerequisite files that have been
modified since the target was last modified, or if the target does not
exist.  The execution of these updates may occur concurrently.</p>
        <p>The rule file syntax is the following.</p>
        <pre class="screen">target: [ prerequisites ... ]
 [TAB]  command1
 [TAB]  -command2 # ignore errors
 [TAB]  @command3 # suppress echoing</pre>
        <p>Here "<code class="literal">[TAB]</code>" is a TAB code.  Each line is interpreted by
the shell after make variable substitution.  Use "<code class="literal">\</code>" at
the end of a line to continue the script.  Use "<code class="literal">$$</code>" to
enter "<code class="literal">$</code>" for environment values for a shell script.</p>
        <p>Implicit rules for the target and prerequisites can be written, for example,
by the following.</p>
        <pre class="screen">%.o: %.c header.h</pre>
        <p>Here, the target contains the character "<code class="literal">%</code>" (exactly one
of them). The "<code class="literal">%</code>" can match any nonempty substring in the
actual target filenames. The prerequisites likewise use
"<code class="literal">%</code>" to show how their names relate to the actual target
name.</p>
        <div class="table">
          <a id="listofmakeautomaticvariables"/>
          <p class="title">
            <strong>Tabla 12.10. List of make automatic variables</strong>
          </p>
          <div class="table-contents">
            <table class="table" summary="List of make automatic variables" border="1">
              <colgroup>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
              </colgroup>
              <thead>
                <tr>
                  <th style="text-align: left">
    variable automática
    </th>
                  <th style="text-align: left">
    valor
    </th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td style="text-align: left">
                <code class="literal">$@</code>
              </td>
                  <td style="text-align: left">
    target
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">$&lt;</code>
              </td>
                  <td style="text-align: left">
    first prerequisite
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">$?</code>
              </td>
                  <td style="text-align: left">
    all newer prerequisites
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">$^</code>
              </td>
                  <td style="text-align: left">
    all prerequisites
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">$*</code>
              </td>
                  <td style="text-align: left">
    "<code class="literal">%</code>" matched stem in the target pattern
    </td>
                </tr>
              </tbody>
            </table>
          </div>
        </div>
        <br class="table-break"/>
        <div class="table">
          <a id="listofmakevariableexpansions"/>
          <p class="title">
            <strong>Tabla 12.11. List of make variable expansions</strong>
          </p>
          <div class="table-contents">
            <table class="table" summary="List of make variable expansions" border="1">
              <colgroup>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
              </colgroup>
              <thead>
                <tr>
                  <th style="text-align: left">
    expansión variable
    </th>
                  <th style="text-align: left">
    descripción
    </th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td style="text-align: left">
                <code class="literal">foo1 := bar</code>
              </td>
                  <td style="text-align: left">
    expansión por única vez
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">foo2 = bar</code>
              </td>
                  <td style="text-align: left">
    expansión recursiva
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                <code class="literal">foo3 += bar</code>
              </td>
                  <td style="text-align: left">
    anexar
    </td>
                </tr>
              </tbody>
            </table>
          </div>
        </div>
        <br class="table-break"/>
        <p>Run "<code class="literal">make -p -f/dev/null</code>" to see automatic internal
rules.</p>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_c"/>12.3. C</h2>
            </div>
          </div>
        </div>
        <p>You can set up proper environment to compile programs written in the <a class="ulink" href="https://es.wikipedia.org/wiki/C_(lenguaje_de_programación)">C programming language</a> by the
following.</p>
        <pre class="screen"># apt-get install glibc-doc manpages-dev libc6-dev gcc build-essential</pre>
        <p>The <code class="literal">libc6-dev</code> package, i.e., GNU C Library, provides
<a class="ulink" href="https://es.wikipedia.org/wiki/Biblioteca_estándar_de_C">C standard library</a> which is
collection of header files and library routines used by the C programming
language.</p>
        <p>See references for C as the following.</p>
        <div class="itemizedlist">
          <ul class="itemizedlist">
            <li class="listitem">
              <p>
"<code class="literal">info libc</code>" (C library function reference)
</p>
            </li>
            <li class="listitem">
              <p><span class="citerefentry"><span class="refentrytitle">gcc</span>(1)</span>
y "<code class="literal">info gcc</code>"
</p>
            </li>
            <li class="listitem">
              <p><span class="citerefentry"><span class="refentrytitle">each_C_library_function_name</span>(3)</span>
</p>
            </li>
            <li class="listitem">
              <p>
Kernighan &amp; Ritchie, "The C Programming Language", 2nd edition (Prentice
Hall)
</p>
            </li>
          </ul>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_simple_c_program_gcc"/>12.3.1. Programa sencillo en C (gcc)</h3>
              </div>
            </div>
          </div>
          <p>Se puede crear un ejecutable "<code class="literal">ejecutable_de_ejemplo</code>"
utilizando la biblioteca "<code class="literal">libm</code>" mediante este sencillo
ejemplo.</p>
          <pre class="screen">$ cat &gt; ejemplo.c &lt;&lt; EOF
#include &lt;stdio.h&gt;
#include &lt;math.h&gt;
#include &lt;string.h&gt;

int main(int argc, char **argv, char **envp){
        double x;
        char y[11];
        x=sqrt(argc+7.5);
        strncpy(y, argv[0], 10); /* evita el desbordamiento */
        y[10] = '\0'; /* asegura que la cadena finaliza con '\0' */
        printf("%5i, %5.3f, %10s, %10s\n", argc, x, y, argv[1]);
        return 0;
}
EOF
$ gcc -Wall -g -o ejecutable_de_ejemplo ejemplo..c -lm
$ ./ejecutable_de_ejemplo
        1, 2.915, ./run_exam,     (null)
$ ./run_example 1234567890qwerty
        2, 3.082, ./run_exam, 1234567890qwerty</pre>
          <p>Aquí, se necesita "<code class="literal">-lm</code>" para enlazar la biblioteca
"<code class="literal">/usr/lib/libm.so</code>" del paquete <code class="literal">libc6</code>
para utilizar la función
<span class="citerefentry"><span class="refentrytitle">sqrt</span>(3)</span>.
La biblioteca actual está ubicada en "<code class="literal">/lib/</code>" con el
nombre de archivo "<code class="literal">libm.so.6</code>", el cual es un enlace
simbólico a "<code class="literal">libm-2.7.so</code>".</p>
          <p>Mire el último elemento de la salida. Tiene incluso más de 10 caracteres a
pesar de tener  "<code class="literal">%10s</code>".</p>
          <p>La utilización de operaciones de punteros sin comprobar los límites, como
ocurre con
<span class="citerefentry"><span class="refentrytitle">sprintf</span>(3)</span>
y
<span class="citerefentry"><span class="refentrytitle">strcpy</span>(3)</span>,
no se utilizan para evitar el desbordamiento del buffer que puede provocar
problemas desconocidos. En su lugar se utilizan
<span class="citerefentry"><span class="refentrytitle">snprintf</span>(3)</span>
y
<span class="citerefentry"><span class="refentrytitle">strncpy</span>(3)</span>.</p>
        </div>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_debug"/>12.4. Depuración</h2>
            </div>
          </div>
        </div>
        <p>La depuración es una de las actividades más importantes de la
programación. Conocer como depurar un programa le convierte en un usuario de
Debian mejor que puede aportar informes de error relevantes.</p>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_basic_gdb_execution"/>12.4.1. Fundamentos de gdb</h3>
              </div>
            </div>
          </div>
          <p>El principal <a class="ulink" href="https://es.wikipedia.org/wiki/Depurador">depurador</a> en Debian es
<span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>
el cual permite inspeccionar un programa mientras se ejecuta.</p>
          <p>Instalemo <code class="literal">gdb</code> y otros programas relevantes com se
muestra.</p>
          <pre class="screen"># apt-get install gdb gdb-doc build-essential devscripts</pre>
          <p>Puede encontrar un buen tutorial de <code class="literal">gdb</code> en "<code class="literal">info
gdb</code>" y mucha más información <a class="ulink" href="http://www.unknownroad.com/rtfm/gdbtut/gdbtoc.html">a
través de Internet</a>.  Aquí hay un ejemplo sencillo de la utilización
de
<span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>
en un "<code class="literal">programa</code>" que ha sido compilado para producir
información de depuración con la opción "<code class="literal">-g</code>".</p>
          <pre class="screen">$ gdb programa
(gdb) b 1                # pone un punto de ruptura en la línea 1
(gdb) run args           # ejecuta el programa con args
(gdb) next               # siguiente línea
...
(gdb) step               # paso hacia adelante
...
(gdb) p parm             # imprime el valor de parm
...
(gdb) p parm=12          # le asigna el valor de 12
...
(gdb) quit</pre>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Existen abreviaturas para la mayor parte de las órdenes de
<span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>.
La expansión del tabulador funciona de la misma manera que en el intérprete
de órdenes.</p>
                </td>
              </tr>
            </table>
          </div>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_debugging_the_debian_package"/>12.4.2. Depurando un paquete Debian</h3>
              </div>
            </div>
          </div>
          <p>Por defecto, en un paquete normal, los binarios del sistema Debian deben
estar limpios por lo que la mayor parte de los símbolos del sistema son
eliminados. Para depurar un paquete Debian con
<span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>,
se necesita la instalación de los paquetes <code class="literal">*-dbg</code>
(p. ej. <code class="literal">libc6-dbg</code> en el caso de la
<code class="literal">libc6</code>).</p>
          <p>If a package to be debugged does not provide its <code class="literal">*-dbg</code>
package, you need to install it after rebuilding it by the following.</p>
          <pre class="screen">$ mkdir /path/new ; cd /path/new
$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo apt-get install fakeroot devscripts build-essential
$ sudo apt-get build-dep source_package_name
$ apt-get source package_name
$ cd package_name*</pre>
          <p>Fix bugs if needed.</p>
          <p>Bump package version to one which does not collide with official Debian
versions, e.g. one appended with "<code class="literal">+debug1</code>" when
recompiling existing package version, or one appended with
"<code class="literal">~pre1</code>" when compiling unreleased package version by the
following.</p>
          <pre class="screen">$ dch -i</pre>
          <p>Compile and install packages with debug symbols by the following.</p>
          <pre class="screen">$ export DEB_BUILD_OPTIONS=nostrip,noopt
$ debuild
$ cd ..
$ sudo debi package_name*.changes</pre>
          <p>You need to check build scripts of the package and ensure to use
"<code class="literal">CFLAGS=-g -Wall</code>" for compiling binaries.</p>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_obtaining_backtrace"/>12.4.3. Obtaining backtrace</h3>
              </div>
            </div>
          </div>
          <p>When you encounter program crash, reporting bug report with cut-and-pasted
backtrace information is a good idea.</p>
          <p>The backtrace can be obtained by the following steps.</p>
          <div class="itemizedlist">
            <ul class="itemizedlist">
              <li class="listitem">
                <p>
Run the program under
<span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>.
</p>
              </li>
              <li class="listitem">
                <p>
Reproduce crash.
</p>
                <div class="itemizedlist">
                  <ul class="itemizedlist">
                    <li class="listitem">
                      <p>
It causes you to be dropped back to the <code class="literal">gdb</code> prompt.
</p>
                    </li>
                  </ul>
                </div>
              </li>
              <li class="listitem">
                <p>
Type "<code class="literal">bt</code>" at the <code class="literal">gdb</code> prompt.
</p>
              </li>
            </ul>
          </div>
          <p>In case of program freeze, you can crash the program by pressing
<code class="literal">Ctrl-C</code> in the terminal running <code class="literal">gdb</code> to
obtain <code class="literal">gdb</code> prompt.</p>
          <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Tip">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Sugerencia]" src="images/tip.png"/>
                </td>
                <th align="left">Sugerencia</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Often, you see a backtrace where one or more of the top lines are in
"<code class="literal">malloc()</code>" or "<code class="literal">g_malloc()</code>". When this
happens, chances are your backtrace isn't very useful. The easiest way to
find some useful information is to set the environment variable
"<code class="literal">$MALLOC_CHECK_</code>" to a value of 2
(<span class="citerefentry"><span class="refentrytitle">malloc</span>(3)</span>).
You can do this while running <code class="literal">gdb</code> by doing the following.</p>
                </td>
              </tr>
            </table>
          </div>
          <pre class="screen"> $ MALLOC_CHECK_=2 gdb hello</pre>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_advanced_gdb_commands"/>12.4.4. Advanced gdb commands</h3>
              </div>
            </div>
          </div>
          <div class="table">
            <a id="listofadvancedgdbcommands"/>
            <p class="title">
              <strong>Tabla 12.12. List of advanced gdb commands</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of advanced gdb commands" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    orden
    </th>
                    <th style="text-align: left">
    description for command objectives
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">(gdb) thread apply all bt</code>
                </td>
                    <td style="text-align: left">
    get a backtrace for all threads for multi-threaded program
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">(gdb) bt full</code>
                </td>
                    <td style="text-align: left">
    get parameters came on the stack of function calls
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">(gdb) thread apply all bt full</code>
                </td>
                    <td style="text-align: left">
    get a backtrace and parameters as the combination of the preceding options
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">(gdb) thread apply all bt full 10</code>
                </td>
                    <td style="text-align: left">
    get a backtrace and parameters for top 10 calls to cut off irrelevant output
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                  <code class="literal">(gdb) set logging on</code>
                </td>
                    <td style="text-align: left">
    write log of <code class="literal">gdb</code> output to a file (the default is
"<code class="literal">gdb.txt</code>")
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_debugging_x_errors"/>12.4.5. Debugging X Errors</h3>
              </div>
            </div>
          </div>
          <p>If a GNOME program <code class="literal">preview1</code> has received an X error, you
should see a message as follows.</p>
          <pre class="screen">The program 'preview1' received an X Window System error.</pre>
          <p>If this is the case, you can try running the program with
"<code class="literal">--sync</code>", and break on the
"<code class="literal">gdk_x_error</code>" function in order to obtain a backtrace.</p>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_check_dependency_on_libraries"/>12.4.6. Check dependency on libraries</h3>
              </div>
            </div>
          </div>
          <p>Use
<span class="citerefentry"><span class="refentrytitle">ldd</span>(1)</span>
to find out a program's dependency on libraries by the followings.</p>
          <pre class="screen">$ ldd /bin/ls
        librt.so.1 =&gt; /lib/librt.so.1 (0x4001e000)
        libc.so.6 =&gt; /lib/libc.so.6 (0x40030000)
        libpthread.so.0 =&gt; /lib/libpthread.so.0 (0x40153000)
        /lib/ld-linux.so.2 =&gt; /lib/ld-linux.so.2 (0x40000000)</pre>
          <p>For
<span class="citerefentry"><span class="refentrytitle">ls</span>(1)</span>
to work in a `chroot`ed environment, the above libraries must be available
in your `chroot`ed environment.</p>
          <p>See <a class="xref" href="ch09.es.html#_tracing_program_activities" title="9.3.6. Trazando la actividad de un programa">Sección 9.3.6, “Trazando la actividad de un programa”</a>.</p>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_memory_leak_detection_tools"/>12.4.7. Memory leak detection tools</h3>
              </div>
            </div>
          </div>
          <p>There are several memory leak detection tools available in Debian.</p>
          <div class="table">
            <a id="listofmemoryleakdetectiontools"/>
            <p class="title">
              <strong>Tabla 12.13. List of memory leak detection tools</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of memory leak detection tools" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    paquete
    </th>
                    <th style="text-align: left">
    popularidad
    </th>
                    <th style="text-align: left">
    tamaño
    </th>
                    <th style="text-align: left">
    descripción
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/libc6-dev">
<code class="literal">libc6-dev</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=libc6-dev">V:269, I:615</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/libc/libc6-dev.html">15628</a>
                    </td>
                    <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">mtrace</span>(1)</span>:
malloc debugging functionality in glibc
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/valgrind">
<code class="literal">valgrind</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=valgrind">V:8, I:56</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/v/valgrind.html">70463</a>
                    </td>
                    <td style="text-align: left">
    memory debugger and profiler
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/kmtrace">
<code class="literal">kmtrace</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=kmtrace">V:1, I:18</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/k/kmtrace.html">351</a>
                    </td>
                    <td style="text-align: left">
    KDE memory leak tracer using glibc's
<span class="citerefentry"><span class="refentrytitle">mtrace</span>(1)</span>
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/alleyoop">
<code class="literal">alleyoop</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=alleyoop">V:0, I:1</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/a/alleyoop.html">655</a>
                    </td>
                    <td style="text-align: left">
    GNOME front-end to the Valgrind memory checker
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/electric-fence">
<code class="literal">electric-fence</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=electric-fence">V:0, I:6</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/e/electric-fence.html">70</a>
                    </td>
                    <td style="text-align: left"><span class="citerefentry"><span class="refentrytitle">malloc</span>(3)</span>
debugger
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/leaktracer">
<code class="literal">leaktracer</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=leaktracer">V:0, I:2</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/l/leaktracer.html">56</a>
                    </td>
                    <td style="text-align: left">
    memory-leak tracer for C++ programs
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/libdmalloc5">
<code class="literal">libdmalloc5</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=libdmalloc5">V:0, I:3</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/libd/libdmalloc5.html">360</a>
                    </td>
                    <td style="text-align: left">
    debug memory allocation library
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_static_code_analysis_tools"/>12.4.8. Static code analysis tools</h3>
              </div>
            </div>
          </div>
          <p>There are <a class="ulink" href="http://es.wikipedia.org/wiki/Lint">lint</a> like tools for <a class="ulink" href="https://es.wikipedia.org/wiki/Anexo:Herramientas_para_el_análisis_estático_de_software">static code analysis</a>.</p>
          <div class="table">
            <a id="listoftoolsforstaticcodeanalysis"/>
            <p class="title">
              <strong>Tabla 12.14. List of tools for static code analysis</strong>
            </p>
            <div class="table-contents">
              <table class="table" summary="List of tools for static code analysis" border="1">
                <colgroup>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                  <col style="text-align: left"/>
                </colgroup>
                <thead>
                  <tr>
                    <th style="text-align: left">
    paquete
    </th>
                    <th style="text-align: left">
    popularidad
    </th>
                    <th style="text-align: left">
    tamaño
    </th>
                    <th style="text-align: left">
    descripción
    </th>
                  </tr>
                </thead>
                <tbody>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/splint">
<code class="literal">splint</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=splint">V:0, I:5</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/s/splint.html">1889</a>
                    </td>
                    <td style="text-align: left">
    tool for statically checking C programs for bugs
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/flawfinder">
<code class="literal">flawfinder</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=flawfinder">V:0, I:1</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/f/flawfinder.html">175</a>
                    </td>
                    <td style="text-align: left">
    tool to examine C/C++ source code and looks for security weaknesses
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/perl"> <code class="literal">perl</code>
</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=perl">V:610, I:996</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/p/perl.html">651</a>
                    </td>
                    <td style="text-align: left">
    interpreter with internal static code checker:
<span class="citerefentry"><span class="refentrytitle">B::Lint</span>(3perl)</span>
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/pylint">
<code class="literal">pylint</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=pylint">V:6, I:15</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/p/pylint.html">945</a>
                    </td>
                    <td style="text-align: left">
    Python code static checker
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/weblint-perl">
<code class="literal">weblint-perl</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=weblint-perl">V:0, I:2</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/w/weblint-perl.html">34</a>
                    </td>
                    <td style="text-align: left">
    syntax and minimal style checker for HTML
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/linklint">
<code class="literal">linklint</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=linklint">V:0, I:1</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/l/linklint.html">343</a>
                    </td>
                    <td style="text-align: left">
    fast link checker and web site maintenance tool
    </td>
                  </tr>
                  <tr>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.debian.org/sid/libxml2-utils">
<code class="literal">libxml2-utils</code> </a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://qa.debian.org/popcon.php?package=libxml2-utils">V:24, I:318</a>
                    </td>
                    <td style="text-align: left">
                      <a class="ulink" href="http://packages.qa.debian.org/libx/libxml2-utils.html">177</a>
                    </td>
                    <td style="text-align: left">
    utilities with
<span class="citerefentry"><span class="refentrytitle">xmllint</span>(1)</span>
to validate XML files
    </td>
                  </tr>
                </tbody>
              </table>
            </div>
          </div>
          <br class="table-break"/>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_disassemble_binary"/>12.4.9. Disassemble binary</h3>
              </div>
            </div>
          </div>
          <p>You can disassemble binary code with
<span class="citerefentry"><span class="refentrytitle">objdump</span>(1)</span>
by the following.</p>
          <pre class="screen">$  objdump -m i386 -b binary -D /usr/lib/grub/x86_64-pc/stage1</pre>
          <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Note">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Nota]" src="images/note.png"/>
                </td>
                <th align="left">Nota</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p><span class="citerefentry"><span class="refentrytitle">gdb</span>(1)</span>
may be used to disassemble code interactively.</p>
                </td>
              </tr>
            </table>
          </div>
        </div>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_flex_a_better_lex"/>12.5. Flex — a better Lex</h2>
            </div>
          </div>
        </div>
        <p><a class="ulink" href="http://en.wikipedia.org/wiki/Flex_lexical_analyser">Flex</a> is a <a class="ulink" href="http://es.wikipedia.org/wiki/Lex_(informática)">Lex</a>-compatible fast <a class="ulink" href="https://es.wikipedia.org/wiki/Compilador#Análisis_léxico">lexical analyzer</a> generator.</p>
        <p>Tutorial for
<span class="citerefentry"><span class="refentrytitle">flex</span>(1)</span>
can be found in "<code class="literal">info flex</code>".</p>
        <p>You need to provide your own "<code class="literal">main()</code>" and
"<code class="literal">yywrap()</code>".  Otherwise, your flex program should look
like this to compile without a library.  This is because that
"<code class="literal">yywrap</code>" is a macro and "<code class="literal">%option main</code>"
turns on "<code class="literal">%option noyywrap</code>" implicitly.</p>
        <pre class="screen">%option main
%%
.|\n    ECHO ;
%%</pre>
        <p>Alternatively, you may compile with the "<code class="literal">-lfl</code>" linker
option at the end of your
<span class="citerefentry"><span class="refentrytitle">cc</span>(1)</span>
command line (like AT&amp;T-Lex with "<code class="literal">-ll</code>").  No
"<code class="literal">%option</code>" is needed in this case.</p>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_bison_a_better_yacc"/>12.6. Bison — a better Yacc</h2>
            </div>
          </div>
        </div>
        <p>Several packages provide a <a class="ulink" href="http://es.wikipedia.org/wiki/Yacc">Yacc</a>-compatible
lookahead <a class="ulink" href="http://es.wikipedia.org/wiki/Analizador_sintáctico_LR">LR parser</a> or <a class="ulink" href="http://en.wikipedia.org/wiki/LALR_parser">LALR parser</a> generator in Debian.</p>
        <div class="table">
          <a id="listofyacccompatparsergenerators"/>
          <p class="title">
            <strong>Tabla 12.15. List of Yacc-compatible LALR parser generators</strong>
          </p>
          <div class="table-contents">
            <table class="table" summary="List of Yacc-compatible LALR parser generators" border="1">
              <colgroup>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
              </colgroup>
              <thead>
                <tr>
                  <th style="text-align: left">
    paquete
    </th>
                  <th style="text-align: left">
    popularidad
    </th>
                  <th style="text-align: left">
    tamaño
    </th>
                  <th style="text-align: left">
    descripción
    </th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/bison"> <code class="literal">bison</code>
</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=bison">V:10, I:113</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/b/bison.html">2061</a>
                  </td>
                  <td style="text-align: left">
                <a class="ulink" href="https://es.wikipedia.org/wiki/GNU_Bison">GNU LALR parser generator</a>
              </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/byacc"> <code class="literal">byacc</code>
</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=byacc">V:0, I:7</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/b/byacc.html">160</a>
                  </td>
                  <td style="text-align: left">
    Berkeley LALR parser generator
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/btyacc">
<code class="literal">btyacc</code> </a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=btyacc">V:0, I:0</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/b/btyacc.html">207</a>
                  </td>
                  <td style="text-align: left">
    backtracking parser generator based on <code class="literal">byacc</code>
    </td>
                </tr>
              </tbody>
            </table>
          </div>
        </div>
        <br class="table-break"/>
        <p>Tutorial for
<span class="citerefentry"><span class="refentrytitle">bison</span>(1)</span>
can be found in "<code class="literal">info bison</code>".</p>
        <p>You need to provide your own "<code class="literal">main()</code>" and
"<code class="literal">yyerror()</code>".  "<code class="literal">main()</code>" calls
"<code class="literal">yyparse()</code>" which calls "<code class="literal">yylex()</code>",
usually created with Flex.</p>
        <pre class="screen">%%

%%</pre>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_autoconf"/>12.7. Autoconf</h2>
            </div>
          </div>
        </div>
        <p><a class="ulink" href="https://es.wikipedia.org/wiki/Autoconf">Autoconf</a> is a tool for producing shell
scripts that automatically configure software source code packages to adapt
to many kinds of Unix-like systems using the entire GNU build system.</p>
        <p><span class="citerefentry"><span class="refentrytitle">autoconf</span>(1)</span>
produces the configuration script
"<code class="literal">configure</code>". "<code class="literal">configure</code>" automatically
creates a customized "<code class="literal">Makefile</code>" using the
"<code class="literal">Makefile.in</code>" template.</p>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_compile_and_install_a_program"/>12.7.1. Compile and install a program</h3>
              </div>
            </div>
          </div>
          <div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
            <table border="0" summary="Warning">
              <tr>
                <td rowspan="2" align="center" valign="top">
                  <img alt="[Aviso]" src="images/warning.png"/>
                </td>
                <th align="left">Aviso</th>
              </tr>
              <tr>
                <td align="left" valign="top">
                  <p>Do not overwrite system files with your compiled programs when installing
them.</p>
                </td>
              </tr>
            </table>
          </div>
          <p>Debian does not touch files in "<code class="literal">/usr/local/</code>" or
"<code class="literal">/opt</code>".  So if you compile a program from source, install
it into "<code class="literal">/usr/local/</code>" so it does not interfere with
Debian.</p>
          <pre class="screen">$ cd src
$ ./configure --prefix=/usr/local
$ make
$ make install # this puts the files in the system</pre>
        </div>
        <div class="section">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="_uninstall_program"/>12.7.2. Uninstall program</h3>
              </div>
            </div>
          </div>
          <p>If you have the original source and if it uses
<span class="citerefentry"><span class="refentrytitle">autoconf</span>(1)</span>/<span class="citerefentry"><span class="refentrytitle">automake</span>(1)</span>
and if you can remember how you configured it, execute as follows to
uninstall the program.</p>
          <pre class="screen">$ ./configure "all-of-the-options-you-gave-it"
# make uninstall</pre>
          <p>Alternatively, if you are absolutely sure that the install process puts
files only under "<code class="literal">/usr/local/</code>" and there is nothing
important there, you can erase all its contents by the following.</p>
          <pre class="screen"># find /usr/local -type f -print0 | xargs -0 rm -f</pre>
          <p>If you are not sure where files are installed, you should consider using
<span class="citerefentry"><span class="refentrytitle">checkinstall</span>(8)</span>
from the <code class="literal">checkinstall</code> package, which provides a clean
path for the uninstall.  It now supports to create a Debian package with
"<code class="literal">-D</code>" option.</p>
        </div>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_perl_short_script_madness"/>12.8. Perl short script madness</h2>
            </div>
          </div>
        </div>
        <p>Although any <a class="ulink" href="https://es.wikipedia.org/wiki/AWK">AWK</a> scripts can be automatically
rewritten in <a class="ulink" href="http://es.wikipedia.org/wiki/Perl">Perl</a> using
<span class="citerefentry"><span class="refentrytitle">a2p</span>(1)</span>,
one-liner AWK scripts are best converted to one-liner Perl scripts manually.</p>
        <p>Let's think following AWK script snippet.</p>
        <pre class="screen">awk '($2=="1957") { print $3 }' |</pre>
        <p>This is equivalent to any one of the following lines.</p>
        <pre class="screen">perl -ne '@f=split; if ($f[1] eq "1957") { print "$f[2]\n"}' |</pre>
        <pre class="screen">perl -ne 'if ((@f=split)[1] eq "1957") { print "$f[2]\n"}' |</pre>
        <pre class="screen">perl -ne '@f=split; print $f[2] if ( $f[1]==1957 )' |</pre>
        <pre class="screen">perl -lane 'print $F[2] if $F[1] eq "1957"' |</pre>
        <pre class="screen">perl -lane 'print$F[2]if$F[1]eq+1957' |</pre>
        <p>The last one is a riddle.  It took advantage of following Perl features.</p>
        <div class="itemizedlist">
          <ul class="itemizedlist">
            <li class="listitem">
              <p>
The whitespace is optional.
</p>
            </li>
            <li class="listitem">
              <p>
The automatic conversion exists from number to the string.
</p>
            </li>
          </ul>
        </div>
        <p>See
<span class="citerefentry"><span class="refentrytitle">perlrun</span>(1)</span>
for the command-line options.  For more crazy Perl scripts, <a class="ulink" href="http://perlgolf.sourceforge.net">Perl Golf</a> may be interesting.</p>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_web"/>12.9. Web</h2>
            </div>
          </div>
        </div>
        <p>Basic interactive dynamic web pages can be made as follows.</p>
        <div class="itemizedlist">
          <ul class="itemizedlist">
            <li class="listitem">
              <p>
Queries are presented to the browser user using <a class="ulink" href="https://es.wikipedia.org/wiki/HTML">HTML</a> forms.
</p>
            </li>
            <li class="listitem">
              <p>
Filling and clicking on the form entries sends one of the following <a class="ulink" href="http://es.wikipedia.org/wiki/Localizador_Uniforme_de_Recursos">URL</a> string with encoded parameters from the browser to
the web server.
</p>
              <div class="itemizedlist">
                <ul class="itemizedlist">
                  <li class="listitem">
                    <p>
"<code class="literal">http://www.foo.dom/cgi-bin/program.pl?VAR1=VAL1&amp;VAR2=VAL2&amp;VAR3=VAL3</code>"
</p>
                  </li>
                  <li class="listitem">
                    <p>
"<code class="literal">http://www.foo.dom/cgi-bin/program.py?VAR1=VAL1&amp;VAR2=VAL2&amp;VAR3=VAL3</code>"
</p>
                  </li>
                  <li class="listitem">
                    <p>
"<code class="literal">http://www.foo.dom/program.php?VAR1=VAL1&amp;VAR2=VAL2&amp;VAR3=VAL3</code>"
</p>
                  </li>
                </ul>
              </div>
            </li>
            <li class="listitem">
              <p>
"<code class="literal">%nn</code>" in URL is replaced with a character with
hexadecimal <code class="literal">nn</code> value.
</p>
            </li>
            <li class="listitem">
              <p>
The environment variable is set as: "<code class="literal">QUERY_STRING="VAR1=VAL1
VAR2=VAL2 VAR3=VAL3"</code>".
</p>
            </li>
            <li class="listitem">
              <p><a class="ulink" href="https://es.wikipedia.org/wiki/Interfaz_de_entrada_común">CGI</a> program (any one of
"<code class="literal">program.*</code>") on the web server executes itself with the
environment variable "<code class="literal">$QUERY_STRING</code>".
</p>
            </li>
            <li class="listitem">
              <p><code class="literal">stdout</code> of CGI program is sent to the web browser and is
presented as an interactive dynamic web page.
</p>
            </li>
          </ul>
        </div>
        <p>For security reasons it is better not to hand craft new hacks for parsing
CGI parameters.  There are established modules for them in Perl and Python.
<a class="ulink" href="http://es.wikipedia.org/wiki/PHP">PHP</a> comes with these functionalities.  When
client data storage is needed, <a class="ulink" href="https://es.wikipedia.org/wiki/Cookie_(informática)">HTTP
cookies</a> are used.  When client side data processing is needed,
<a class="ulink" href="https://es.wikipedia.org/wiki/JavaScript">Javascript</a> is frequently used.</p>
        <p>For more, see the <a class="ulink" href="https://es.wikipedia.org/wiki/Interfaz_de_entrada_común">Common Gateway
Interface</a>, <a class="ulink" href="https://es.wikipedia.org/wiki/Apache_Software_Foundation">The Apache
Software Foundation</a>, and <a class="ulink" href="https://es.wikipedia.org/wiki/JavaScript">JavaScript</a>.</p>
        <p>Searching "CGI tutorial" on Google by typing encoded URL <a class="ulink" href="http://www.google.com/search?hl=en&amp;ie=UTF-8&amp;q=CGI+tutorial">http://www.google.com/search?hl=en&amp;ie=UTF-8&amp;q=CGI+tutorial</a>
directly to the browser address is a good way to see the CGI script in
action on the Google server.</p>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_the_source_code_translation"/>12.10. The source code translation</h2>
            </div>
          </div>
        </div>
        <p>There are programs to convert source codes.</p>
        <div class="table">
          <a id="listofsourcecodetranslationtools"/>
          <p class="title">
            <strong>Tabla 12.16. List of source code translation tools</strong>
          </p>
          <div class="table-contents">
            <table class="table" summary="List of source code translation tools" border="1">
              <colgroup>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
                <col style="text-align: left"/>
              </colgroup>
              <thead>
                <tr>
                  <th style="text-align: left">
    paquete
    </th>
                  <th style="text-align: left">
    popularidad
    </th>
                  <th style="text-align: left">
    tamaño
    </th>
                  <th style="text-align: left">
    palabra clave
    </th>
                  <th style="text-align: left">
    descripción
    </th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/perl"> <code class="literal">perl</code>
</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=perl">V:610, I:996</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/p/perl.html">651</a>
                  </td>
                  <td style="text-align: left">
    AWK→PERL
    </td>
                  <td style="text-align: left">
    convert source codes from AWK to PERL:
<span class="citerefentry"><span class="refentrytitle">a2p</span>(1)</span>
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/f2c"> <code class="literal">f2c</code>
</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=f2c">V:0, I:7</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/f/f2c.html">433</a>
                  </td>
                  <td style="text-align: left">
    FORTRAN→C
    </td>
                  <td style="text-align: left">
    convert source codes from FORTRAN 77 to C/C++:
<span class="citerefentry"><span class="refentrytitle">f2c</span>(1)</span>
    </td>
                </tr>
                <tr>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.debian.org/sid/intel2gas">
<code class="literal">intel2gas</code> </a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://qa.debian.org/popcon.php?package=intel2gas">V:0, I:0</a>
                  </td>
                  <td style="text-align: left">
                    <a class="ulink" href="http://packages.qa.debian.org/i/intel2gas.html">174</a>
                  </td>
                  <td style="text-align: left">
    intel→gas
    </td>
                  <td style="text-align: left">
    converter from NASM (Intel format) to the GNU Assembler (GAS)
    </td>
                </tr>
              </tbody>
            </table>
          </div>
        </div>
        <br class="table-break"/>
      </div>
      <div class="section">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title"><a id="_making_debian_package"/>12.11. Making Debian package</h2>
            </div>
          </div>
        </div>
        <p>If you want to make a Debian package, read followings.</p>
        <div class="itemizedlist">
          <ul class="itemizedlist">
            <li class="listitem">
              <p><a class="xref" href="ch02.es.html" title="Capítulo 2. Gestión de paquetes Debian">Capítulo 2, <em>Gestión de paquetes Debian</em></a> to understand the basic package
system
</p>
            </li>
            <li class="listitem">
              <p><a class="xref" href="ch02.es.html#_porting_a_package_to_the_stable_system" title="2.7.13. Portar un paquete a un sistema estable">Sección 2.7.13, “Portar un paquete a un sistema estable”</a> to understand
basic porting process
</p>
            </li>
            <li class="listitem">
              <p><a class="xref" href="ch09.es.html#_chroot_system" title="9.10.4. Sistemas chroot">Sección 9.10.4, “Sistemas chroot”</a> to understand basic chroot techniques
</p>
            </li>
            <li class="listitem">
              <p><span class="citerefentry"><span class="refentrytitle">debuild</span>(1)</span>,
<span class="citerefentry"><span class="refentrytitle">pbuilder</span>(1)</span>
and
<span class="citerefentry"><span class="refentrytitle">pdebuild</span>(1)</span>
</p>
            </li>
            <li class="listitem">
              <p><a class="xref" href="ch12.es.html#_debugging_the_debian_package" title="12.4.2. Depurando un paquete Debian">Sección 12.4.2, “Depurando un paquete Debian”</a> for recompiling for
debugging
</p>
            </li>
            <li class="listitem">
              <p><a class="ulink" href="https://www.debian.org/doc/devel-manuals#maint-guide">Debian New Maintainers'
Guide</a> as tutorial (the <code class="literal">maint-guide</code> package)
</p>
            </li>
            <li class="listitem">
              <p><a class="ulink" href="https://www.debian.org/doc/manuals/developers-reference/">Debian Developer's
Reference</a> (the <code class="literal">developers-reference</code> package)
</p>
            </li>
            <li class="listitem">
              <p><a class="ulink" href="https://www.debian.org/doc/devel-manuals.es.html#policy">Debian Policy Manual</a> (the
<code class="literal">debian-policy</code> package)
</p>
            </li>
            <li class="listitem">
              <p><a class="ulink" href="http://www.debian.org/doc/manuals/debmake-doc/">Guide for Debian
Maintainers</a> (the <code class="literal">debmake-doc</code> package)
</p>
            </li>
          </ul>
        </div>
        <p>There are packages such as <code class="literal">debmake</code>,
<code class="literal">dh-make</code>, <code class="literal">dh-make-perl</code>, etc., which
help packaging.</p>
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