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<h3 class="section" id="troff-and-nroff-Modes-1">5.14 <code class="code">troff</code> and <code class="code">nroff</code> Modes</h3>
<a class="index-entry-id" id="index-troff-mode"></a>
<a class="index-entry-id" id="index-mode_002c-troff"></a>
<a class="index-entry-id" id="index-nroff-mode"></a>
<a class="index-entry-id" id="index-mode_002c-nroff"></a>
<p>Historically, <code class="code">nroff</code> and <code class="code">troff</code> were two separate programs;
the former for terminal output, the latter for typesetters. GNU
<code class="code">troff</code> merges both functions into one executable<a class="footnote" id="DOCF68" href="groff.html_fot.html#FOOT68"><sup>68</sup></a> that sends its output to a
device driver (<code class="code">grotty</code> for terminal devices, <code class="code">grops</code> for
PostScript, and so on) which interprets this intermediate output format.
When discussing <abbr class="acronym">AT&T</abbr> <code class="code">troff</code>, it makes sense to talk
about <em class="dfn"><code class="code">nroff</code> mode</em> and <em class="dfn"><code class="code">troff</code> mode</em> since the
differences are hard-coded. GNU <code class="code">troff</code> takes information from
device and font description files without handling requests specially if
a terminal output device is used, so such a strong distinction is
unnecessary.
</p>
<p>Usually, a macro package can be used with all output devices.
Nevertheless, it is sometimes necessary to make a distinction between
terminal and non-terminal devices: GNU <code class="code">troff</code> provides two
built-in conditions ‘<samp class="samp">n</samp>’ and ‘<samp class="samp">t</samp>’ for the <code class="code">if</code>, <code class="code">ie</code>,
and <code class="code">while</code> requests to decide whether GNU <code class="code">troff</code> shall
behave like <code class="code">nroff</code> or like <code class="code">troff</code>.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002etroff"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.troff</code></strong><a class="copiable-link" href='#index-_002etroff'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-troff"></a>
<a class="index-entry-id" id="index-troffrc-4"></a>
<a class="index-entry-id" id="index-troffrc_002dend-2"></a>
<p>Make the ‘<samp class="samp">t</samp>’ built-in condition true (and the ‘<samp class="samp">n</samp>’ built-in
condition false) for <code class="code">if</code>, <code class="code">ie</code>, and <code class="code">while</code> conditional
requests. This is the default if GNU <code class="code">troff</code> (<em class="emph">not</em>
<code class="code">groff</code>) is started with the <samp class="option">-R</samp> switch to avoid loading of
the startup files <samp class="file">troffrc</samp> and <samp class="file">troffrc-end</samp>. Without
<samp class="option">-R</samp>, GNU <code class="code">troff</code> stays in <code class="code">troff</code> mode if the output
device is not a terminal (e.g., ‘ps’).
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002enroff"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.nroff</code></strong><a class="copiable-link" href='#index-_002enroff'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-nroff"></a>
<a class="index-entry-id" id="index-tty_002etmac"></a>
<p>Make the ‘<samp class="samp">n</samp>’ built-in condition true (and the ‘<samp class="samp">t</samp>’ built-in
condition false) for <code class="code">if</code>, <code class="code">ie</code>, and <code class="code">while</code> conditional
requests. This is the default if GNU <code class="code">troff</code> uses a terminal
output device; the code for switching to <code class="code">nroff</code> mode is in the
file <samp class="file">tty.tmac</samp>, which is loaded by the startup file
<code class="code">troffrc</code>.
</p></dd></dl>
<p>See <a class="xref" href="Conditionals-and-Loops.html">Conditionals and Loops</a>, for more details on built-in conditions.
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