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          <td align="right"><i>Making TeX Work</i> Version 1.0.1
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    <div class="chapter">
      <div class="titlepage">
        <div>
          <h2 class="title"><a id="chap.running"
          name="chap.running"></a>Chapter&#160;3.&#160;Running
          TeX</h2>
        </div>

        <div>
          <p class="releaseinfo">$Revision: 1.1 $</p>
        </div>

        <div>
          <p class="pubdate">$Date: 2002/08/23 14:31:13 $</p>
        </div>
        <hr class="component-separator" />
      </div>

      <p>The heart of processing a document with TeX is running<a
      id="id2862591" class="indexterm" name="id2862591"></a><a
      id="id2862603" class="indexterm" name="id2862603"></a> the
      TeX program. In this chapter, you'll learn what happens
      between the time you first start the TeX program and the time
      it finishes. You'll also learn what files TeX really needs
      (in addition to your document) and what to do when TeX finds
      things in your document that it doesn't understand.</p>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a
            id="run.sec.formatfiles"
            name="run.sec.formatfiles"></a>What Do You Run?</h2>
          </div>
        </div>

        <p>The first thing you have to know is what program to run.
        Unfortunately, the actual file you have to execute varies
        between platforms and implementations. If you have built
        and/or installed TeX yourself, you probably already know
        what program to run. You'll have to ask your system
        administrator for help if you can't figure out what the
        name of the TeX executable is on your computer. The rest of
        this chapter assumes that the command <tt>tex</tt> runs
        TeX. You should substitute the name of the executable
        program on your own system for <tt>tex</tt><a
        id="id2862504" class="indexterm" name="id2862504"></a> in
        the examples that follow.</p>

        <p>Most implementations of TeX have some hard-coded memory
        limits<a id="id2862517" class="indexterm"
        name="id2862517"></a>. These limitations may cause problems
        if you are trying to run a very complex document through
        TeX. To combat this problem, some distributions include two
        versions of the TeX executable. One version is a
        &#8220;small&#8221; TeX<a id="id2862533" class="indexterm"
        name="id2862533"></a><a id="id2862543" class="indexterm"
        name="id2862543"></a> that generally runs faster but has
        less memory available to process your documents. The other
        version, a &#8220;big&#8221; TeX<a id="id2869219"
        class="indexterm" name="id2869219"></a><a id="id2869229"
        class="indexterm" name="id2869229"></a>, can process more
        complex documents but may run more slowly. If you get a
        &#8220;TeX capacity exceeded&#8221; error, and you have a
        big TeX available on your system, try processing your
        document with the big TeX.</p>

        <p>If you still get an error, you have a document that is
        simply too complex for your implementation of TeX to
        handle, or you have an error in one of the macros in your
        document. By examining the error log, described later in
        this chapter in the section &#8220;<a
        href="ch03.html#sec.logfiles" title="Log Files">the section
        called &#8220;Log Files&#8221;</a>,&#8221; you can
        determine what macro TeX is interpreting when the error
        occurs. If the error occurs in a macro that you wrote,
        check to make sure the macro functions the way you intended
        by using it in a small test document.</p>
      </div>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a id="id2869278"
            name="id2869278"></a>What Files Does TeX Need?</h2>
          </div>
        </div>

        <p>Naturally, TeX needs your input file in order to process
        it. However, TeX must be able to find several other files<a
        id="id2869287" class="indexterm" name="id2869287"></a><a
        id="id2869299" class="indexterm" name="id2869299"></a> as
        well. The files that TeX needs are normally created during
        the installation process. Here is a common directory layout
        for TeX on a unix system:</p>

        <div class="informaltable">
          <table border="1">
            <colgroup>
              <col />
              <col />
            </colgroup>

            <tbody>
              <tr>
                <td><tt>/usr/local/lib/tex/formats</tt></td>

                <td>Format files</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/pool</tt></td>

                <td>Pool files</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/formats</tt></td>

                <td>Format files</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/inputs</tt></td>

                <td>&#8220;System&#8221; input files</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/macros</tt></td>

                <td>(styles, macros, and miscellaneous</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/lib</tt></td>

                <td>files distributed with TeX)</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/ps</tt></td>

                <td>PostScript support files</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/fonts/pk</tt></td>

                <td><tt>PK</tt> fonts</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/fonts/vf</tt></td>

                <td>Virtual fonts</td>
              </tr>

              <tr>
                <td><tt>/usr/local/lib/tex/fonts/tfm</tt></td>

                <td><tt>TFM</tt> metrics</td>
              </tr>
            </tbody>
          </table>
        </div>

        <p>A similar layout is frequently used on other operating
        systems, except that the TeX files are often stored in a
        top-level directory (for example, <tt>C:$\$TEX</tt> under
        MS-DOS). Because TeX is very flexible and has many
        different implementations, the exact directory structure
        varies. Pool files are sometimes placed in the format file
        directory (which is sometimes called <tt>fmt</tt> or
        <tt>fmts</tt>, rather than <tt>formats</tt>). Input files
        may occur in one or more of the standard places listed
        above (<tt>inputs</tt>, <tt>macros</tt>, and <tt>lib</tt>)
        as well as a number of other places (<tt>texinputs</tt> is
        another common name).</p>

        <p>The files under the TeX tree usually come from outside
        distributions, so you don't have to change them often. (You
        definitely <span class="emphasis"><em>shouldn't</em></span>
        put your personal macro files in that tree, even if you do
        have access to it.)</p>

        <p>The following sections describe, in more detail, each of
        the files that TeX needs.</p>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2869610"
              name="id2869610"></a>Pool Files</h3>
            </div>
          </div>

          <p>Pool files contain string constants used by TeX at
          runtime. Each time TeX is compiled, it creates a pool
          file<a id="id2869621" class="indexterm"
          name="id2869621"></a> unique to the version being
          compiled. The pool file from one version of TeX will not
          work with a different version.</p>

          <p>In contrast to format files (discussed in the next
          section), if you don't have a pool file, there's nothing
          you can do about it. If you obtained precompiled programs
          (from the Internet, from a friend, or commercially) and
          you don't have a pool file, you received an incomplete
          distribution.</p>

          <p>If you did not install TeX yourself, but find that the
          pool file is missing, contact the system administrator
          who performed the installation. He or she did something
          wrong.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2869651"
              name="id2869651"></a>Format Files</h3>
            </div>
          </div>

          <p>As mentioned in the section &#8220;<a
          href="ch01.html#sec.tex.controlsequences"
          title="Boxes and Glue">the section called &#8220;Boxes
          and Glue&#8221;</a>&#8221; in Chapter&#160;<a
          href="ch01.html"
          title="Chapter&#160;1.&#160;The Big Picture">Chapter&#160;1</a>,
          <span class="emphasis"><em><a href="ch01.html"
          title="Chapter&#160;1.&#160;The Big Picture">Chapter&#160;1</a></em></span>,
          all of the control sequences and macros that your
          document uses must be defined somewhere. One way to do
          this is to use the \input command to load all of the
          definitions at the beginning of each document. However,
          with large macro packages like LaTeX, this process can be
          very time consuming. Format files<a id="id2869699"
          class="indexterm" name="id2869699"></a> are a way of
          predefining control sequences and macros so they don't
          have to be interpreted by TeX every time they're used. If
          TeX didn't use format files, you'd have to wait for TeX
          to interpret all of LaTeX every time you processed a
          document that used LaTeX.</p>

          <p><a id="run.sec.initexintro"
          name="run.sec.initexintro"></a>Format files are created
          by a special version of TeX, usually called iniTeX<a
          id="id2869724" class="indexterm" name="id2869724"></a>.
          Some implementations combine TeX and iniTeX into one
          program. In this case, you must select iniTeX with a
          special option when you run TeX. IniTeX interprets all
          the control sequences in a macro package and builds the
          in-memory data structures that the TeX program needs.
          After loading the whole macro package, iniTeX writes the
          memory image it has constructed to a format file. When
          TeX later loads the format file, it simply copies it into
          memory; no interpretation is necessary. This is why
          loading a format file is such a fast way to define
          control sequences<a id="id2869736" class="indexterm"
          name="id2869736"></a>. This is also why format files are
          not usually portable from one system to another,<sup>[<a
          id="id2869760" name="id2869760"
          href="#ftn.id2869760">25</a>]</sup> or even between
          different versions of TeX on the same system. Different
          versions of TeX are stored differently in memory, and
          this difference in loading makes the format files
          incompatible. For this reason, you need a
          &#8220;big&#8221; iniTeX to make format files for a big
          TeX and a &#8220;small&#8221; iniTeX for a small TeX.</p>

          <p>You will find a complete discussion of macro packages
          and instructions for building format files for many of
          the common macro packages in Chapter&#160;<a
          href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a>,
          <span class="emphasis"><em><a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a></em></span>.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="sec.userfiles"
              name="sec.userfiles"></a>User Files</h3>
            </div>
          </div>

          <p>When you run TeX<a id="id2869826" class="indexterm"
          name="id2869826"></a>, you have to tell it what file to
          process. If you specify a complete pathname, TeX will
          load the specific file that you request. For example, I
          could process the document <tt>myreport.tex</tt> in the
          directory <tt>/home/norm/tex/</tt> by running:</p>
<pre class="screen">
\$ <span class="bold"><b>tex /home/norm/tex/myreport</b></span>
</pre>

          <p>This example applies to both unix and PC
          implementations of TeX. Even though MS-DOS and OS/2
          typically use the backslash to separate directory names,
          <span class="emphasis"><em>always</em></span> use a
          forward slash when entering filenames for TeX.</p>

          <p>If you specify a simple filename without a path, TeX
          looks for the file in several user-defined and, possibly,
          system-defined locations. In the following example, TeX
          will attempt to locate the file <tt>myreport.tex</tt> in
          order to process it:</p>
<pre class="screen">
\$ <span class="bold"><b>tex myreport</b></span>
</pre>

          <p>If the file <tt>myreport.tex</tt> exists in several
          directories, TeX will process the first file it finds
          without looking for any others. TeX always prints the
          complete name of the file it processes both on the
          display and in the log file, so you can always tell what
          file was really processed.</p>

          <p>The most common way to specify user-defined locations
          is by setting the <tt>TEXINPUTS</tt> environment
          variable<sup>[<a id="id2869931" name="id2869931"
          href="#ftn.id2869931">26</a>]</sup> to a list of
          subdirectories where TeX documents are kept. Setting
          <tt>TEXINPUTS</tt> specifies where TeX should look for
          <span class="emphasis"><em>documents</em></span> (files
          that you input with \input or some other construct, style
          files, and macros). To change where TeX looks for other
          kinds of files (fonts, formats, pool files, etc.),
          setting different environment variables or performing
          some other customization is required. The format of the
          environment variable differs according to the platform
          you use. On unix systems, it is a list of directory names
          separated by colons. Here is a typical example:</p>
<pre class="screen">
.:/usr/local/lib/tex/inputs:/home/norm/tex/inputs
</pre>

          <p>On MS-DOS and OS/2 systems, it is a list of directory
          names separated by semicolons. A typical example looks
          like this:<sup>[<a id="id2869999" name="id2869999"
          href="#ftn.id2869999">27</a>]</sup></p>
<pre class="screen">
.;\tex\inputs;\tex\styles;\tex\macros
</pre>

          <p>Consult the documentation for your particular
          implementation of TeX for more information about
          system-defined locations where TeX looks for input files.
          Unfortunately, this is not always well documented. For
          example, an undocumented feature of version 1.4s of emTeX
          always searches in the directory
          <tt>\emtex\texinputs</tt> even if it does not occur in
          the <tt>TEXINPUTS</tt> path. In fact, there is no way to
          tell it <span class="emphasis"><em>not</em></span> to
          look there, short of renaming the directory (which is
          what I did).</p>

          <p>If TeX cannot find a file you specify, for example
          <tt>rpt-data.tex</tt>, it displays a prompt like this
          one:</p>
<pre class="screen">
! I can't find file `rpt-data.tex'.
&lt;*&gt; \input rpt-data

Please type another input filename:
</pre>

          <p>The general form of TeX error messages is discussed in
          the section called &#8220;<a href="ch03.html#sec.errors"
          title="What About Errors?">the section called &#8220;What
          About Errors?&#8221;</a>&#8221; later in this chapter.
          TeX announces an error by printing the error message on a
          line that begins with an exclamation mark. Below the
          error, TeX provides the context in which the error
          occurred. In the example above, TeX encountered the
          command \input rpt-data and tried to find the file
          <tt>rpt-data.tex</tt> which it could not locate.</p>

          <p>Notice that TeX automatically added the extension
          <tt>.tex</tt><a id="id2870120" class="indexterm"
          name="id2870120"></a> to the name of the file it was
          looking for. In any context where you specify a filename,
          TeX will append <tt>.tex</tt> unless you specify an
          alternate extension.</p>

          <p>TeX responds to a &#8220;can't find file&#8221; error
          by asking you to type the name of a different file. Some
          implementations of TeX allow you to abort by typing
          Ctrl-C or Ctrl-D at this point,<sup>[<a id="id2870149"
          name="id2870149" href="#ftn.id2870149">28</a>]</sup> but
          other implementations insist that you enter a filename.
          In this case, you'll find it convenient to create an
          empty file called <tt>nul.tex</tt><a id="id2870165"
          class="indexterm" name="id2870165"></a> in a directory in
          your <tt>TEXINPUTS</tt> path so you can get around this
          requirement by supplying a dummy answer to the prompt.
          <tt>nul.tex</tt> is part of many standard
          distributions.</p>
        </div>
      </div>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a
            id="sec.clineopts" name="sec.clineopts"></a>The Command
            Line</h2>
          </div>
        </div>

        <p>Except for the name of a document, TeX has very few
        command-line options<a id="id2870206" class="indexterm"
        name="id2870206"></a>. The only option that is regularly
        used is the name of a format file, but the use of this
        option is frequently buried inside a batch file or shell
        script.</p>

        <p>It is helpful to think of TeX, LaTeX, SliTeX,
        etc.&#160;as different text processors (they aren't really;
        they're all TeX with different format files). This illusion
        is easy to provide with shell scripts or batch files. For
        example, on an MS-DOS system, you could easily have three
        batch files called <tt>tex.bat</tt>, <tt>latex.bat</tt>,
        and <tt>slitex.bat</tt>:</p>

        <div class="itemizedlist">
          <ul type="disc">
            <li>
              <p>The <tt>tex.bat</tt> file runs the TeX executable
              with the <tt>plain</tt> format file specified as an
              option.</p>
            </li>

            <li>
              <p>The <tt>latex.bat</tt> file runs TeX with the
              <tt>lplain</tt> format file.</p>
            </li>

            <li>
              <p>The <tt>slitex.bat</tt> file runs TeX with the
              <tt>splain</tt> format file.</p>
            </li>
          </ul>
        </div>

        <p>Now typing <span class="bold"><b>tex <span
        class="emphasis"><em>filename</em></span></b></span>
        processes Plain TeX documents; typing <span
        class="bold"><b>latex <span
        class="emphasis"><em>filename</em></span></b></span>
        processes LaTeX documents; and typing <span
        class="bold"><b>slitex <span
        class="emphasis"><em>filename</em></span></b></span>
        processes SliTeX documents.<sup>[<a id="id2870360"
        name="id2870360" href="#ftn.id2870360">29</a>]</sup> The
        role of format files and macro packages is described fully
        in Chapter&#160;<a href="ch04.html"
        title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a>,
        <span class="emphasis"><em><a href="ch04.html"
        title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a></em></span>.</p>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="sec.runtex.cmdcautions"
              name="sec.runtex.cmdcautions"></a>Command-line
              Options</h3>
            </div>
          </div>

          <p>A formal specification of the TeX command line<a
          id="id2870407" class="indexterm" name="id2870407"></a>
          looks like this:</p>

          <div class="informalexample">
<pre class="screen">
$ tex &lt;<span
class="emphasis"><em>switches</em></span>&gt; &lt;&amp;<span
class="emphasis"><em>format</em></span>&gt; &lt;|<span
class="emphasis"><em>document</em></span>&gt; &lt;<span
class="emphasis"><em>tex-commands</em></span>&gt;
</pre>
          </div>

          <p>If this looks confusing, have no fear. I'll explain
          what it means in English.</p>

          <p>After the name of the TeX program (or batch file), the
          first things that can go on the command line are
          implementation-dependent switches and options. For
          example, implementations of TeX that combine iniTeX and
          TeX into a single program may use <span
          class="bold"><b>/I</b></span> as the switch to specify
          that iniTeX processing<a id="id2870468" class="indexterm"
          name="id2870468"></a> is desired (iniTeX, you may
          remember, was described in the section &#8220;<a
          href="ch03.html#run.sec.formatfiles"
          title="What Do You Run?">the section called &#8220;What
          Do You Run?&#8221;</a>,&#8221; earlier in this chapter).
          There are no system-independent switches for TeX. Consult
          the documentation that comes with your implementation for
          more information about system-dependent switches.</p>

          <p>After any system-dependent switches, the first thing
          that you can put on the TeX command line is the name of
          the format file<a id="id2870509" class="indexterm"
          name="id2870509"></a> to use. If you specify this option,
          you must include it before any other options, and you
          must put an ampersand (&amp;)<a id="id2870520"
          class="indexterm" name="id2870520"></a> in front of the
          format file name. If you do not specify a format file,
          TeX will use a default format, usually Plain TeX.</p>

          <p>After the format, TeX looks for the name of a document
          to process. If TeX finds a filename on the command line,
          it will process the document<a id="id2870537"
          class="indexterm" name="id2870537"></a> contained in that
          file before looking at any other options that may
          follow.</p>

          <p>Finally, you can insert arbitrary TeX commands on the
          command line by typing them just as you would in a
          document. The section &#8220;<a
          href="ch02.html#sec.texcomp" title="Running TeX">the
          section called &#8220;Running TeX&#8221;</a>&#8221; in
          Chapter&#160;<a href="ch02.html"
          title="Chapter&#160;2.&#160;Editing">Chapter&#160;2</a>,
          <span class="emphasis"><em><a href="ch02.html"
          title="Chapter&#160;2.&#160;Editing">Chapter&#160;2</a></em></span>,
          describes one particular instance where this is very
          useful, but it isn't something that you are likely to do
          very often.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2870602"
              name="id2870602"></a>Command-line Cautions</h3>
            </div>
          </div>

          <p>There are some special restrictions on file names used
          on the command line and on the way TeX interprets the
          command line. These restrictions are summarized here.</p>

          <div class="section">
            <div class="titlepage">
              <div>
                <h4 class="title"><a id="run.sec.misinterpret"
                name="run.sec.misinterpret"></a>Misinterpretation
                of the command line</h4>
              </div>
            </div>

            <p>Command lines that are typed at the operating system
            prompt are actually seen by your operating system's
            &#8220;command processor&#8221; before they are seen by
            TeX. You must be aware of special processing that might
            be performed by the command processor. Under unix, for
            example, the backslash<a id="id2870634"
            class="indexterm" name="id2870634"></a> is frequently
            interpreted as a <span class="emphasis"><em>shell
            escape</em></span> character<a id="id2870656"
            class="indexterm" name="id2870656"></a>, and the
            ampersand<a id="id2870668" class="indexterm"
            name="id2870668"></a> has another special meaning
            related to job control<a id="id2870677"
            class="indexterm" name="id2870677"></a>. The ampersand
            is also special under some MS-DOS and OS/2 command
            processors where it is the default command separation
            character and will not be passed to TeX as you would
            expect.</p>

            <p>To insert these troublesome characters literally,
            you must enclose the relevant sections of the command
            line in quotation marks<a id="id2870695"
            class="indexterm" name="id2870695"></a> or use some
            form of shell escape mechanism. Under unix, place the
            name of the format file, including the ampersand, in
            double or single quotes and use two backslashes in a
            row if you include TeX control sequences on the command
            line. For example, type:</p>

            <div class="informalexample">
<pre class="screen">
$ <span
class="bold"><b>tex '&amp;lplain' \\nonstopmode \\input doc1</b></span>
</pre>
            </div>

            <p>instead of</p>

            <div class="informalexample">
<pre class="screen">
$ <span
class="bold"><b>tex &amp;lplain \nonstopmode \input doc1</b></span>
</pre>
            </div>

            <p>When using OS/2, place a ^ in front of an ampersand
            to prevent it from being interpreted as a command
            separator.</p>
          </div>

          <div class="section">
            <div class="titlepage">
              <div>
                <h4 class="title"><a id="sec.runtex.texwoopts"
                name="sec.runtex.texwoopts"></a>Filenames and
                TeX</h4>
              </div>
            </div>

            <p><a id="id2870772" class="indexterm"
            name="id2870772"></a><a id="id2870779"
            class="indexterm" name="id2870779"></a> <a
            id="id2870793" class="indexterm" name="id2870793"></a>
            It is easy for TeX to recognize the presence of a
            format file on the command line; it must be the first
            option and it must begin with an ampersand.<sup>[<a
            id="id2870805" name="id2870805"
            href="#ftn.id2870805">30</a>]</sup> After the format
            file, TeX determines whether the next option is a file
            name by looking at the first character of the option.
            If the first character is not a backslash, it is a
            filename; otherwise it is a TeX command, and TeX
            assumes that no filename is present.</p>

            <p>On some systems, notably MS-DOS and OS/2, the
            backslash<a id="id2870848" class="indexterm"
            name="id2870848"></a> is used to delimit the
            subdirectory components of a file name. On other
            systems, a forward slash is used. Regardless of the
            system you use, filenames passed to TeX <span
            class="emphasis"><em>must</em></span> use forward
            slashes to delimit filenames.</p>

            <p>For example, TeX will not process the file
            <tt>letter.tex</tt> in the <tt>\tex\docs</tt> directory
            of the current drive if you execute the following
            command line on an MS-DOS system:</p>

            <div class="informalexample">
<pre class="screen">
\$ <span class="bold"><b>tex \tex\docs\letter</b></span>
</pre>
            </div>

            <p>Instead, you must type the following, regardless of
            the operating system you're using:</p>

            <div class="informalexample">
<pre class="screen">
\$ <span class="bold"><b>tex /tex/docs/letter</b></span>
</pre>
            </div>

            <p>If you don't, TeX will complain that the control
            sequence \tex is undefined. Even more confusing errors
            may result if the first subdirectory happens to be a
            valid control sequence.</p>

            <p>Unfortunately, filenames containing forward slashes
            are not always recognized by operating systems that use
            backslashes to delimit filenames. For example, under
            MS-DOS, <tt>IF EXIST C:/CONFIG.SYS</tt> returns
            false,<a id="id2870956" class="indexterm"
            name="id2870956"></a> even when a file called
            <tt>config.sys</tt> exists in the root directory of
            drive C:. Therefore, it is most convenient to use
            filenames with backslashes when other commands will be
            used (for example in a batch file). Filenames in batch
            files must have any backslashes translated into forward
            slashes before being passed to TeX. MS-DOS's command
            processor isn't really powerful enough, but the task is
            quite doable with JP Software<a id="id2870971"
            class="indexterm" name="id2870971"></a>'s <b>4DOS</b>
            command processor. <b>4DOS</b><a id="id2871000"
            class="indexterm" name="id2871000"></a> is a
            replacement for MS-DOS's normal command processor; it
            offers many advantages over the normal processor. You
            can get a shareware version of <b>4DOS</b> from many
            large MS-DOS archive sites on the Internet<sup>[<a
            id="id2871022" name="id2871022"
            href="#ftn.id2871022">31</a>]</sup> as well as most
            large bulletin board systems. The following lines,
            written in <b>4DOS</b><a id="id2871048"
            class="indexterm" name="id2871048"></a>'s extended
            batch language, will translate all backslashes in the
            environment variable <tt>TEXFN</tt> to forward
            slashes:</p>
<pre class="screen">
:FixBacks
  Set Count=%@Index[%TexFn,\]
  If "%Count" eq "-1" Goto FixDone
  Set Place=%@Eval[%Count+1]
  Set TexFn=%@SubStr[%TexFn,0,%Count]/%@SubStr[%TexFn,%Place]
  Goto FixBacks
:FixDone
</pre>

            <p>These lines also work under OS/2 with JP Software's
            <b>4OS2</b> command processor (akin to <b>4DOS</b>;
            shareware versions of <b>4OS2</b> are also available).
            The same task can be completed in a single line with
            <b>REXX</b><a id="id2871106" class="indexterm"
            name="id2871106"></a> under OS/2:</p>
<pre class="screen">
TEXFN = TRANSLATE(TEXFN, '\', '/')
</pre>

            <p><b>REXX</b> is an interpreted systems-programming
            language distributed with OS/2. <b>REXX</b> runs under
            many other IBM operating systems in addition to OS/2.
            Several versions of <b>REXX</b> are available for
            MS-DOS and unix systems, too.</p>
          </div>

          <div class="section">
            <div class="titlepage">
              <div>
                <h4 class="title"><a id="id2871151"
                name="id2871151"></a>Multiple documents</h4>
              </div>
            </div>

            <p>Keep in mind<a id="id2871161" class="indexterm"
            name="id2871161"></a> that TeX interprets only the
            first option after the format file name as a document
            name. If you type the command line:</p>

            <div class="informalexample">
<pre class="screen">
\$ <span class="bold"><b>tex doc1 doc2</b></span>
</pre>
            </div>

            <p>TeX will process only <tt>doc1.tex</tt> as a
            document. The result of the above command line<a
            id="id2871206" class="indexterm" name="id2871206"></a>
            will be exactly as if you had typed the literal word
            &#8220;doc2&#8221; at the very end of the file
            <tt>doc1.tex</tt>.</p>

            <p>To get TeX to process both <tt>doc1</tt> and
            <tt>doc2</tt> as documents, type a command like the
            following:</p>

            <div class="informalexample">
<pre class="screen">
\$ <span class="bold"><b>tex doc1 \input doc2</b></span>
</pre>
            </div>

            <p>or, for complete clarity,</p>

            <div class="informalexample">
<pre class="screen">
\$ <span class="bold"><b>tex \input doc1 \input doc2</b></span>
</pre>
            </div>

            <p>In either case, the structure of your document files
            must allow them to be concatenated together. TeX does
            not process <tt>doc1</tt> and then process
            <tt>doc2</tt> separately. Instead, it processes all of
            <tt>doc1</tt> and appends the text in the file
            <tt>doc2</tt> directly onto the end of
            <tt>doc1</tt>.</p>
          </div>
        </div>
      </div>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a id="id2871334"
            name="id2871334"></a>TeX Without Options</h2>
          </div>
        </div>

        <p>If you run TeX without specifying any options<a
        id="id2871343" class="indexterm" name="id2871343"></a> at
        all, it prints out some introductory information, then
        produces a <tt>**</tt> prompt<a id="id2871366"
        class="indexterm" name="id2871366"></a> and stops. Here's
        what emTeX's <tt>tex386</tt> produces:</p>
<pre class="screen">
This is emTeX (tex386), Version 3.141 [3c-beta8]
**
</pre>

        <p>This is the only situation where the <tt>**</tt> prompt
        occurs. TeX now expects you to enter text. TeX will
        interpret anything you type after the <tt>**</tt> prompt
        <span class="emphasis"><em>exactly</em></span> as if you
        had typed it on the command line. All of the rules
        regarding slashes (described in &#8220;<a
        href="ch03.html#run.sec.misinterpret"
        title="Misinterpretation of the command line">the section
        called &#8220;Misinterpretation of the command
        line&#8221;</a>&#8221; earlier) apply to commands that you
        type at the <tt>**</tt> prompt. Remember, however, that
        input entered at the <tt>**</tt> prompt is not seen by the
        operating system, so don't use quotation marks or doubled
        backslashes.</p>

        <p>The last line of a document is usually a command telling
        TeX that the document is finished. TeX responds by writing
        the last page of the document and ending (returning control
        to the operating system). If a document doesn't end with
        such a command, TeX will wait for more input. When TeX runs
        out of input, it displays the <tt>*</tt> prompt<a
        id="id2871494" class="indexterm" name="id2871494"></a>
        (single asterisk). Anything you type at the <tt>*</tt>
        prompt is interpreted exactly as if it occurred in the
        document that TeX was processing. You cannot specify an
        alternate format or name a document at the <tt>*</tt>
        prompt. You can, however, use \input to insert another
        file.</p>

        <p>If emTeX processes a document called
        <tt>unended.tex</tt>:</p>
<pre class="screen">
% This is UNENDED.TEX
Now is the time for all good men
to come to the aid of their country.
% Note: there's no \bye command to end 
% TeX's processing...
</pre>

        <p>the following output appears on the terminal:</p>
<pre class="screen">
This is emTeX (tex386), Version 3.141 [3c-beta8]
**unended
(unended.tex)
*
</pre>

        <p>You can exit from the TeX program at the <tt>*</tt>
        prompt by telling TeX that it should stop processing the
        current document. Exactly how you get out depends on the
        format file you use. The following table shows the stop
        commands for some TeX macro packages<a id="id2871573"
        class="indexterm" name="id2871573"></a><a id="id2871590"
        class="indexterm" name="id2871590"></a><a id="id2871603"
        class="indexterm" name="id2871603"></a><a id="id2871616"
        class="indexterm" name="id2871616"></a><a id="id2871626"
        class="indexterm" name="id2871626"></a>.</p>

        <div class="table">
          <a id="id2871639" name="id2871639"></a>

          <p class="title"><b>Table&#160;3.1.&#160;</b></p>

          <table summary="" border="1">
            <colgroup>
              <col align="left" />
              <col align="left" />
            </colgroup>

            <thead>
              <tr>
                <th align="left">Package</th>

                <th align="left">Command</th>
              </tr>
            </thead>

            <tbody>
              <tr>
                <td align="left">Plain TeX</td>

                <td align="left">\bye</td>
              </tr>

              <tr>
                <td align="left">LaTeX</td>

                <td align="left">\end{document}<a id="id2871705"
                class="indexterm" name="id2871705"></a></td>
              </tr>

              <tr>
                <td align="left">SliTeX</td>

                <td align="left">\end{document}</td>
              </tr>

              <tr>
                <td align="left">Lollipop</td>

                <td align="left">\Stop</td>
              </tr>

              <tr>
                <td align="left">TeXinfo</td>

                <td align="left"><tt>@bye</tt></td>
              </tr>
            </tbody>
          </table>
        </div>

        <p>If you do not know which format is in use, you can
        almost always get out with the following steps:<sup>[<a
        id="id2871781" name="id2871781"
        href="#ftn.id2871781">32</a>]</sup></p>

        <div class="orderedlist">
          <ol type="1">
            <li>
              <p>Type a control sequence that TeX will not
              recognize (control sequences \undefined and
              \gobbledygook will work). TeX will respond with the
              question mark prompt.</p>
            </li>

            <li>
              <p>Enter <span class="bold"><b>x</b></span> at the
              prompt. The question mark prompt is discussed fully
              in the section &#8220;<a href="ch03.html#sec.qprompt"
              title="Interpreting TeX Error Messages">the section
              called &#8220;Interpreting TeX Error
              Messages&#8221;</a>,&#8221; later in this
              chapter.</p>
            </li>
          </ol>
        </div>

        <p>To continue the above example, if I type \undefined at
        the <tt>*</tt> prompt, TeX will respond:</p>
<pre class="screen">
This is emTeX (tex386), Version 3.141 [3c-beta8]
**unended
(unended.tex)
*<span class="bold"><b>\undefined</b></span>
! Undefined control sequence.
&lt;*&gt; \undefined

?
</pre>

        <p>If I enter <span class="bold"><b>x</b></span> at the
        question mark prompt, TeX will print several informative
        messages and then end, returning control to the operating
        system.</p>
<pre class="screen">
This is emTeX (tex386), Version 3.141 [3c-beta8]
**unended
(unended.tex)
*\undefined
! Undefined control sequence.
&lt;*&gt; \undefined

? <span class="bold"><b>x</b></span>
No pages of output.
Transcript written on unended.log.
</pre>

        <p>One word of caution: some macro packages redefine the
        meaning of the backslash (\)<a id="id2871940"
        class="indexterm" name="id2871940"></a> character so that
        it doesn't function as the beginning of a control sequence
        (for example, the TeXinfo format uses the at-sign,
        &#8220;@&#8221;). In this case, you must precede the
        undefined control sequence by the escape character, even if
        it isn't the backslash.</p>
      </div>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a
            id="sec.errors" name="sec.errors"></a>What About
            Errors?</h2>
          </div>
        </div>

        <p>When you write TeX documents, you will occasionally make
        mistakes<a id="id2871979" class="indexterm"
        name="id2871979"></a><a id="id2871992" class="indexterm"
        name="id2871992"></a><a id="id2872002" class="indexterm"
        name="id2872002"></a> and as a result, TeX won't be able to
        process your document. There are six broad classes of
        mistakes you're likely to make:</p>

        <div class="orderedlist">
          <ol type="1">
            <li>
              <p>Naming documents or files that TeX cannot
              find.</p>
            </li>

            <li>
              <p>Misspelling the name of a TeX control
              sequence.</p>
            </li>

            <li>
              <p>Failing to close an environment or forgetting to
              insert a closing brace after an opening brace.</p>
            </li>

            <li>
              <p>Using math operators outside of math mode or
              forgetting to close an opened math environment.</p>
            </li>

            <li>
              <p>Requesting a font that TeX cannot find.</p>
            </li>

            <li>
              <p>Everything else.</p>
            </li>
          </ol>
        </div>

        <p>TeX is legitimately criticized for having error messages
        that are very difficult to understand. TeX frequently
        provides far more information than you really need or want,
        and the excess information often obscures the actual cause
        of the error.</p>

        <p>Nevertheless, understanding what TeX does when it
        encounters an error will help make error messages easier to
        understand. Let's begin with an example. Example&#160;<a
        href="ch03.html#ex.badfonttex"
        title="Example&#160;3.1.&#160;The Document BADFONT.TEX">Example&#160;3.1</a>
        shows a simple LaTeX document using the New Font Selection
        Scheme (NFSS), which contains an error.<sup>[<a
        id="id2872107" name="id2872107"
        href="#ftn.id2872107">33</a>]</sup> The error is that the
        control sequence \Large, which has been redefined to
        request a 17pt font, contains a typo:
        \cs[fontsize]{fontsiz} should be \fontsize.<sup>[<a
        id="id2872135" name="id2872135"
        href="#ftn.id2872135">34</a>]</sup></p>

        <div class="example">
          <a id="ex.badfonttex" name="ex.badfonttex"></a>

          <p class="title"><b>Example&#160;3.1.&#160;The Document
          BADFONT.TEX</b></p>
<pre class="screen">
\documentstyle{article}
% The following definition changes the font that LaTeX
% uses for the 'Large' font.  I have introduced a typo
% into the definition, &#8220;\fontsiz&#8221; should be &#8220;\fontsize&#8221;.
% The  first time a \Large font is requested, an error will occur.
\renewcommand{\Large}{\fontsiz{17}{20pt}\selectfont}
\begin{document}

This text precedes the first section header.

% Note: LaTeX uses the \Large font in section
% headers...this will fail in a confusing way
% because the error is deep within the definition
% of \section where \Large is used...
\section{First Section}

This is the first and only sentence of the first section.

\end{document}
</pre>
        </div>

        <p>When TeX processes this file, using LaTeX with the New
        Font Selection Scheme, it produces these error
        messages:</p>
<pre class="screen">
This is TeX, Version 3.1415 (C version 6.1)
LaTeX Version 2.09 &lt;25 March 1992&gt; with NFSS2
(badfont.tex (/work/nutshell/texguide/styles/latex/article.sty
Standard Document Style `article' &lt;14 Jan 92&gt;.
(/work/nutshell/texguide/styles/latex/art10.sty)) (badfont.aux)
(/usr/local/lib/tex/inputs/nfss2/T1cmr.fd)
! Undefined control sequence.
\Large -&gt;\fontsiz{17}{20pt}\selectfont 
&lt;argument&gt; \reset@font \Large 
                              \bf 
\@sect ...x \ifdim \@tempskipa &gt;\z@ \begingroup #6
                                      \relax \@hangfrom {\hskip ...
l.21 \end{section}
\section{First Section}

?
</pre>

        <p>These messages exemplify the kind of confusing error
        messages that TeX produces. Remember the following rule:
        Always look at the first and last line of the TeX error
        message when trying to figure out what went wrong and where
        it went wrong. In this case, the first line is:</p>
<pre class="screen">
! Undefined control sequence.
</pre>

        <p>and the last line is:</p>
<pre class="screen">
l.21 \end{section}
\section{First Section}
</pre>

        <p>The error is that the control sequence
        \cs[fontsize]{fontsiz} is not defined and TeX was
        processing line 21 of the file when it occurred.</p>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="sec.logfiles"
              name="sec.logfiles"></a>Log Files</h3>
            </div>
          </div>

          <p>You don't have to remember or write down the error
          messages that TeX produces. When TeX processes a
          document, it produces a transcript<a id="id2872267"
          class="indexterm" name="id2872267"></a> of everything
          that occurs; you can refer to this transcript later if
          you need to recall what errors occurred when you
          processed your document. TeX stores this transcript in a
          file which has the same name as the document and the
          extension <tt>.log</tt>. For example, if you process
          <tt>main.tex</tt>, TeX produces a transcript in
          <tt>main.log</tt>.</p>

          <div class="note"
          style="margin-left: 0.5in; margin-right: 0.5in;">
            <h3 class="title">Note</h3>

            <p>Log files go in the current directory. TeX always
            places the log file in the current directory, even if
            you specify a path when you format your document. For
            example, if you process <tt>lectures/main.tex</tt>, TeX
            produces a transcript in <tt>main.log</tt>, not in
            <tt>lectures/main.log</tt> as you might expect.</p>
          </div>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="sec.qprompt"
              name="sec.qprompt"></a>Interpreting TeX Error
              Messages</h3>
            </div>
          </div>

          <p>The first line of a TeX error message begins with an
          exclamation point followed by the text of the message<a
          id="id2872354" class="indexterm" name="id2872354"></a>.
          The lines that follow it show the context in which the
          error occurred.<sup>[<a id="id2872367" name="id2872367"
          href="#ftn.id2872367">35</a>]</sup> In the previous
          example, the error message indicates an <tt>Undefined
          control sequence</tt>. This means that TeX encountered a
          control sequence which was not previously defined.</p>

          <p>The final line, which says <tt>l.21 \section{First
          Section}</tt>, occurs right above the question mark
          prompt. It identifies the line in your document that TeX
          was processing when it encountered the error. The error
          occurred when TeX was at line 21 of the file, and that
          line began with <tt>\section{First Section}</tt>.</p>

          <p>Between the first and last lines, TeX prints a
          detailed description of how the error occurred. This is
          necessary because the error may have occurred inside the
          replacement text of a macro that you used. When TeX
          encounters a control sequence, like \section, it has to
          look up the definition to figure out how to typeset your
          document. The definition of a control sequence may
          contain other control sequences which also have to be
          interpreted. It is possible for TeX to be several levels
          deep, as it was in this case, when an error occurs. To
          give the person who wrote the definition of the control
          sequence an opportunity to figure out what went wrong,
          TeX prints out a <span class="emphasis"><em>trace
          back</em></span><a id="id2872434" class="indexterm"
          name="id2872434"></a> of what happened before the error.
          As you gain experience with a particular macro package,
          you'll find the intervening lines more meaningful.</p>

          <p>Correcting an error depends entirely on the nature of
          the error. In this case, all you need to do is correct
          the typo.</p>

          <p>As stated above, there are six general classes of
          errors you might encounter when you run TeX. The
          following sections briefly describe each class.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2872461"
              name="id2872461"></a>Naming a File TeX Cannot
              Find</h3>
            </div>
          </div>

          <p>Missing documents are discussed in the section called
          &#8220;<a href="ch03.html#sec.userfiles"
          title="User Files">the section called &#8220;User
          Files&#8221;</a>,&#8221; earlier in this chapter.</p>

          <p>If you request a format file<a id="id2872489"
          class="indexterm" name="id2872489"></a> that cannot be
          found, TeX issues the following warning message:</p>
<pre class="screen">
Sorry, I can't find that format; will try the default
</pre>

          <p>TeX then attempts to typeset your document with Plain
          TeX.<sup>[<a id="id2872514" name="id2872514"
          href="#ftn.id2872514">36</a>]</sup> To correct this
          problem, run TeX with the correct format file name. If
          the format file isn't available, you will have to build
          it. Chapter&#160;<a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a>,
          <span class="emphasis"><em><a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a></em></span>,
          describes how to build format files for several common
          macro packages.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2872549"
              name="id2872549"></a>Misspelling a Control Sequence
              Name</h3>
            </div>
          </div>

          <p>Misspelling a control sequence name<a id="id2872558"
          class="indexterm" name="id2872558"></a> is one of the
          most common errors. For example, you might type
          \ipnut{chap1} in your document instead of \input{chap1}.
          The solution is straightforward and usually easy to
          identify. In many cases, you can simply proceed after
          encountering this error. Although TeX may not typeset
          your document correctly, you can continue to look for
          other errors. The section called &#8220;<a
          href="ch03.html#sec.qprompt"
          title="Interpreting TeX Error Messages">the section
          called &#8220;Interpreting TeX Error
          Messages&#8221;</a>,&#8221; later in this chapter,
          describes how to continue after an error.</p>

          <p>In some cases, TeX may become badly confused by a
          misspelled control sequence name, in which case you
          should give up and fix the spelling error before trying
          to process your document further. This may happen if you
          misspell a LaTeX environment name (\begin{itemze} instead
          of \begin{itemize}, for example),<sup>[<a id="id2872615"
          name="id2872615" href="#ftn.id2872615">37</a>]</sup>
          which will make LaTeX misinterpret many of the control
          sequences which follow.</p>

          <p>Sometimes TeX will complain that a control sequence is
          undefined when you <span
          class="emphasis"><em>know</em></span> that the control
          sequence is spelled correctly. When this occurs, make
          sure that you are using the correct format file (see the
          section &#8220;<a href="ch03.html#sec.clineopts"
          title="The Command Line">the section called &#8220;The
          Command Line&#8221;</a>&#8221; earlier in this chapter),
          loading the correct macro files, and using the correct
          style options.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2872653"
              name="id2872653"></a>Failure to Close an
              Environment</h3>
            </div>
          </div>

          <p>Failure to close an environment<a id="id2872662"
          class="indexterm" name="id2872662"></a> is another very
          common error. There are several distinct errors in this
          category:</p>

          <div class="itemizedlist">
            <ul type="disc">
              <li>
                <p>Failure to insert a closing brace (<tt>}</tt>)
                for each opening brace may cause a &#8220;TeX
                capacity exceeded&#8221; error when TeX processes
                your document. This happens because sometimes TeX
                tries to read everything between braces into
                memory. If the closing brace is absent, TeX may run
                out of memory.</p>

                <p>If the braces are supposed to enclose the
                argument to a macro, you may also get this error:<a
                id="id2872709" class="indexterm"
                name="id2872709"></a></p>
<pre class="screen">
! Paragraph ended before <span
class="emphasis"><em>macro</em></span> was complete.
</pre>

                <p>In order to help detect errors of this type, TeX
                doesn't ordinarily allow the argument of a macro to
                consist of more than one paragraph, so the first
                blank line after the place where you failed to type
                the closing brace may produce this error.</p>
              </li>

              <li>
                <p>Failure to close a begin/end environment pair
                causes LaTeX to complain about a mismatch when it
                encounters the next
                \end{\texttt{<i><tt>environment</tt></i>}}
                command.<a id="id2872764" class="indexterm"
                name="id2872764"></a></p>
              </li>

              <li>
                <p>If your document ends with an open environment,
                TeX will warn you that:</p>
<pre class="screen">
! (\end occurs inside a group at level <span
class="emphasis"><em>n</em></span>)
</pre>

                <p>where <tt><i><tt>n</tt></i></tt> is the number
                of open groups, usually 1.</p>
              </li>

              <li>
                <p>Failure to close a mathematics environment will
                result in the error:</p>
<pre class="screen">
! Missing $ inserted
</pre>

                <p>when TeX reaches a macro that does not make
                sense in mathematics mode (like \section) or when a
                surrounding group ends.</p>
              </li>
            </ul>
          </div>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2872844"
              name="id2872844"></a>Math Outside of Math Mode</h3>
            </div>
          </div>

          <p>TeX has a lot of operators for special treatment of
          mathematical formulas. These operators must occur inside
          <span class="emphasis"><em>mathematics mode</em></span><a
          id="id2872858" class="indexterm" name="id2872858"></a>,<a
          id="id2872867" class="indexterm" name="id2872867"></a>
          which is usually delimited by dollar signs in your
          document.<a id="id2872879" class="indexterm"
          name="id2872879"></a></p>

          <p>If you attempt to use math operators, superscripts,
          subscripts, or other math-mode control sequences outside
          of mathematics mode, the following error will occur:<a
          id="id2872899" class="indexterm"
          name="id2872899"></a></p>
<pre class="screen">
! Missing $ inserted
</pre>

          <p>This is your clue that a mathematics environment has
          not been closed properly or that you failed to open one
          before using a math-mode operator.</p>

          <p>For example, the underscore character is usually
          defined to be a math-mode operator which starts a
          subscript, in other words <tt>H${}_2$O</tt> produces
          &#8220;H${}_2$O&#8221; in your document.<sup>[<a
          id="id2872944" name="id2872944"
          href="#ftn.id2872944">38</a>]</sup> If you use the
          underscore outside of mathematics mode, such as in
          regular text:</p>
<pre class="screen">
The file &#8220;test_one&#8221; contains the ...
</pre>

          <p>TeX will respond:</p>
<pre class="screen">
! Missing $ inserted
&lt;inserted text&gt;
                $
&lt;to be read again&gt;
                  _
The file &#8220;test_
                one&#8221; contains the ...
?
</pre>

          <p>In LaTeX, the easiest way around this problem is to
          enclose the offending text in a &#8220;verbatim&#8221;
          macro, like this:</p>
<pre class="screen">
  The file &#8220;<tt>test_one</tt>&#8221; contains the ...
</pre>

          <p>Note that the argument to the <tt>macro</tt>is
          delimited by any two identical characters (in this case,
          two &#8220;<tt>+</tt>&#8221; signs).</p>

          <p>In Plain TeX or another format, the problem can be
          circumvented in similar ways; consult the reference for
          the format you are using. Also consult Table&#160;<a
          href="ch01.html#tab.acttype"
          title="Table&#160;1.2.&#160;How to Typeset Special Characters">
          Table&#160;1.2</a> in Chapter&#160;<a href="ch01.html"
          title="Chapter&#160;1.&#160;The Big Picture">Chapter&#160;1</a>,
          <span class="emphasis"><em><a href="ch01.html"
          title="Chapter&#160;1.&#160;The Big Picture">Chapter&#160;1</a></em></span>,
          for a list of special characters and how to type them in
          your documents.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2873082"
              name="id2873082"></a>Missing Fonts</h3>
            </div>
          </div>

          <p>The first<a id="id2873090" class="indexterm"
          name="id2873090"></a> time that you use each font, TeX
          loads font metric information about the font. The font
          metric information, stored in a <tt>TFM</tt> file,
          includes information about the sizes of each character as
          well as kerning and ligature information. These topics
          are discussed fully in Chapter&#160;<a href="ch05.html"
          title="Chapter&#160;5.&#160;Fonts">Chapter&#160;5</a>,
          <span class="emphasis"><em><a href="ch05.html"
          title="Chapter&#160;5.&#160;Fonts">Chapter&#160;5</a></em></span>.</p>

          <p>If you request a font that does not exist, for example
          <tt>crm10</tt> (a misspelling of <tt>cmr10</tt>), TeX
          cannot find a <tt>TFM</tt> file for the font and
          therefore displays:</p>
<pre class="screen">
Font \myfont=crm10 not loadable: Metric (TFM) file not found
</pre>

          <p>This means that TeX attempted to associate the font
          described by the <tt>TFM</tt> file <tt>crm10.tfm</tt>
          with the control sequence \myfont, but the <tt>TFM</tt>
          file didn't exist. You must have a <tt>TFM</tt> file for
          every font that you use.</p>

          <p>A second kind of error---actually, a warning---occurs
          when you are using the New Font Selection Scheme (NFSS)<a
          id="id2873221" class="indexterm" name="id2873221"></a>.
          The NFSS performs font substitution, if possible, when an
          unknown font is requested. The NFSS is described in
          Chapter&#160;<a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a>,
          <span class="emphasis"><em><a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a></em></span>,
          in the &#8220;<a href="ch04.html#sec.latex"
          title="LaTeX">the section called
          &#8220;LaTeX&#8221;</a>&#8221; section.</p>
        </div>

        <div class="section">
          <div class="titlepage">
            <div>
              <h3 class="title"><a id="id2873273"
              name="id2873273"></a>Everything Else</h3>
            </div>
          </div>

          <p>There are, unfortunately, lots of other errors that
          can occur. Some of the errors are directly related to TeX
          while others are warning and error messages associated
          with particular macro packages. There is no way to
          catalog every one of them or suggest what can be done in
          every case.</p>

          <p>The best advice I can offer is to isolate the problem
          in as small a document as possible, consult the
          references you have available very carefully, and, if all
          else fails, forward your problem to one of the electronic
          forums that deal with TeX (the <tt>Info-TeX</tt> mailing
          list<a id="id2873302" class="indexterm"
          name="id2873302"></a> and the <tt>comp.text.tex</tt>
          newsgroup<a id="id2873326" class="indexterm"
          name="id2873326"></a>, for example).</p>
        </div>
      </div>

      <div class="section">
        <div class="titlepage">
          <div>
            <h2 class="title" style="clear: both"><a id="id2873346"
            name="id2873346"></a>The Question Mark Prompt</h2>
          </div>
        </div>
        <a id="id2873352" class="indexterm" name="id2873352"></a>

        <p>When TeX encounters an error, it displays an error
        message and a summary of the error, as described in the
        section called &#8220;<a href="ch03.html#sec.errors"
        title="What About Errors?">the section called &#8220;What
        About Errors?&#8221;</a>&#8221; earlier in this chapter.
        Following the error, TeX normally stops and displays the
        question mark prompt.</p>

        <p>If you type a question mark of your own at the prompt,
        TeX displays the actions available to you:</p>
<pre class="screen">
? ?
Type &lt;return&gt; to proceed,
S to scroll future error messages,
R to run without stopping, Q to run quietly,
I to insert something, E to edit your file,
1 or ... or 9 to ignore the next 1 to 9 tokens
of input, H for help, X to quit.
?
</pre>

        <p>You can type any of the following responses at the
        question mark prompt:<a id="id2873401" class="indexterm"
        name="id2873401"></a></p>

        <div class="variablelist">
          <dl>
            <dt><span class="term">Type <b>Return</b> to
            proceed.</span></dt>

            <dd>
              <p>Simply typing Return will cause TeX to ignore the
              error and proceed. Depending on the nature of the
              error, this may cause more errors immediately or
              later on.</p>
            </dd>

            <dt><span class="term">Type <b>S</b> to scroll future
            error messages.</span></dt>

            <dd>
              <p>Typing <b>S</b> tells TeX to continue and not to
              stop for most future errors. TeX will continue to
              print the error messages, both to the terminal and to
              the log file, but it will not display the question
              mark prompt again.</p>

              <p>TeX will still stop and ask about missing
              files.</p>
            </dd>

            <dt><span class="term">Type <b>R</b> to run without
            stopping.</span></dt>

            <dd>
              <p>The <b>R</b> option is just like <b>S</b> except
              that it tells TeX to ignore missing files as well.
              TeX will proceed blindly forward as best as it can.
              You will still see all of the error messages scroll
              by as TeX proceeds.</p>
            </dd>

            <dt><span class="term">Type <b>Q</b> to run
            quietly.</span></dt>

            <dd>
              <p>This option is just like <b>R</b> except that
              error messages are not displayed on the screen. The
              messages are saved in the log file, however, even
              though they are not displayed.</p>
            </dd>

            <dt><span class="term">Type <b>I</b> to insert
            something.</span></dt>

            <dd>
              <p>If you notice a simple typo, you can correct it
              with the <b>I</b> command. For example, suppose that
              TeX complains of an undefined control sequence:
              \cte{kn:art1}. You recognize that this should have
              been \cite{kn:art1}. You can insert the correct
              control sequence by responding <tt>i\cite</tt> to the
              question mark prompt. TeX will ignore the misspelled
              control sequence and insert the (correct) sequence
              \cite in its place.</p>

              <p>Inserting words or commands at the question mark
              prompt <span class="emphasis"><em>does
              not</em></span> change your input file. It simply
              instructs TeX to <span
              class="emphasis"><em>pretend</em></span> that your
              file contained a different sequence of words and
              commands. You must change the input file with an
              editor, or the same error will occur the next time
              you format the document.</p>
            </dd>

            <dt><span class="term">Type <b>E</b> to edit your
            file.</span></dt>

            <dd>
              <p>This option terminates TeX. If your system is
              configured appropriately, an editor will be loaded
              automatically, and the cursor will be placed at the
              offending line in your input file. This is not
              possible in all environments.</p>
            </dd>

            <dt><span class="term">Type <b><i><tt>n</tt></i></b>,
            where <i><tt>n</tt></i> is a number between 1 and
            9.</span></dt>

            <dd>
              <p>This option tells TeX to ignore some of the input.
              After skipping over the number of <span
              class="emphasis"><em>tokens</em></span> you request,
              TeX returns to the question mark prompt so that you
              can delete more tokens.</p>

              <p>What's a token<a id="id2873692" class="indexterm"
              name="id2873692"></a>? When TeX reads an input file,
              it breaks each line down into the smallest,
              indivisible chunks that have meaning. These are
              called tokens. For the most part, tokens are
              individual characters. The exceptions are control
              sequences<a id="id2873705" class="indexterm"
              name="id2873705"></a>, which are single tokens, and
              white spaces which are also single tokens. There
              <span class="emphasis"><em>are</em></span> other
              exceptions (and more technical definitions of
              &#8220;token&#8221;), but that's the gist of it.</p>
            </dd>

            <dt><span class="term">Type <b>H</b> for
            help.</span></dt>

            <dd>
              <p>Typing <b>H</b> displays a slightly more verbose
              description of the error that occurred and, usually,
              suggests the nature of the corrective action that you
              might take.</p>
            </dd>

            <dt><span class="term">Type <b>X</b> to
            quit.</span></dt>

            <dd>
              <p>Typing <b>X</b> tells TeX to stop immediately and
              ends the TeX program. If there are any completed
              pages (pages processed before the error, in other
              words), they are written to the <tt>DVI</tt> file
              before TeX ends.</p>
            </dd>
          </dl>
        </div>
      </div>

      <div class="footnotes">
        <br />
        <hr width="100" align="left" />

        <div class="footnote">
          <p><sup>[<a id="ftn.id2869760" name="ftn.id2869760"
          href="#id2869760">25</a>]</sup> {The exception occurs in
          some unix versions of TeX where provisions are made for
          different architectures to share the same format files.
          The exact same version of TeX must be running on both
          architectures for this to work.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2869931" name="ftn.id2869931"
          href="#id2869931">26</a>]</sup> {The exact name of the
          environment variable<a id="id2869936" class="indexterm"
          name="id2869936"></a><a id="id2869947" class="indexterm"
          name="id2869947"></a> differs between
          implementations.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2869999" name="ftn.id2869999"
          href="#id2869999">27</a>]</sup> You will notice that I've
          used backslashes<a id="id2870004" class="indexterm"
          name="id2870004"></a> to separate directory components in
          the path. Environment variables are handled by the
          system-dependent portions of TeX, so it's okay to use
          backslashes here. You can also use forward slashes, but I
          use backslashes because that is more typical of MS-DOS
          and OS/2 environments.</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2870149" name="ftn.id2870149"
          href="#id2870149">28</a>]</sup> {MS-DOS and OS/2
          implementations of TeX may use Ctrl-Z (possibly followed
          by a carriage return) instead of Ctrl-C or Ctrl-D.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2870360" name="ftn.id2870360"
          href="#id2870360">29</a>]</sup> {On unix systems, the
          same effect is often achieved with symbolic links. Most
          unix implementations look for different standard format
          files based upon the name of the executable that starts
          them.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2870805" name="ftn.id2870805"
          href="#id2870805">30</a>]</sup> {In the unlikely event
          that you have a TeX document stored in a file with a name
          beginning with an ampersand, use the following trick to
          process that file: instead of running <b>tex
          &amp;file</b>, run <b>tex \input &amp;file</b> (or even
          <b>tex &amp;format \input &amp;file</b>).</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2871022" name="ftn.id2871022"
          href="#id2871022">31</a>]</sup> {For example,
          <tt>oak.oakland.edu</tt> in the directory
          <tt>/pub/msdos/4DOS</tt>.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2871781" name="ftn.id2871781"
          href="#id2871781">32</a>]</sup> {Typing the break
          character (<b>Ctrl-C</b> or <b>Ctrl-Break</b>, for
          example) sometimes works as well, but some
          implementations of TeX don't respond to the break
          character at every prompt. On unix systems, use
          <b>Ctrl-D</b>. EmTeX responds to <b>Ctrl-Z</b> followed
          by <b>Return</b>.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872107" name="ftn.id2872107"
          href="#id2872107">33</a>]</sup> {The details of LaTeX and
          the NFSS are discussed in Chapter&#160;<a
          href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a>,
          <span class="emphasis"><em><a href="ch04.html"
          title="Chapter&#160;4.&#160;Macro Packages">Chapter&#160;4</a></em></span>.
          It is simply convenient to use a concrete example in this
          case. Do not be concerned if you do not use LaTeX or the
          NFSS.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872135" name="ftn.id2872135"
          href="#id2872135">34</a>]</sup> {In practice, redefining
          a control sequence like $\$<tt>Large</tt> in a document
          is a bad idea. I've done it here only to provide an
          example of an error that occurs inside another
          macro.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872367" name="ftn.id2872367"
          href="#id2872367">35</a>]</sup> {The number of lines of
          context shown in the error message is determined by the
          value of the built-in parameter
          $\$<tt>errorcontextlines</tt>.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872514" name="ftn.id2872514"
          href="#id2872514">36</a>]</sup> {It is possible to make
          other formats the default, but in practice I've never
          seen it done.}</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872615" name="ftn.id2872615"
          href="#id2872615">37</a>]</sup> Technically, LaTeX
          environment names are not a control sequence names, but
          they behave in very much the same way in LaTeX.</p>
        </div>

        <div class="footnote">
          <p><sup>[<a id="ftn.id2872944" name="ftn.id2872944"
          href="#id2872944">38</a>]</sup> {The empty curly braces
          are necessary in this example because otherwise there
          wouldn't be anything in front of the subscript command
          for TeX to subscript below. Typically, another digit or
          symbol would come in front of the subscript command. In
          this case, I didn't want the &#8220;H&#8221; and
          &#8220;O&#8221; in the math environment because letters
          are printed in math-italics in math mode.}</p>
        </div>
      </div>
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