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<title>Control Characters (The GNU Troff Manual)</title>
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<div class="subsection-level-extent" id="Control-Characters">
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<h4 class="subsection" id="Control-Characters-1">5.6.1 Control Characters</h4>
<a class="index-entry-id" id="index-control-characters"></a>
<a class="index-entry-id" id="index-configuring-control-characters"></a>
<a class="index-entry-id" id="index-changing-control-characters"></a>
<p>The mechanism of using <code class="code">roff</code>’s control characters to invoke
requests and call macros was introduced in <a class="ref" href="Requests-and-Macros.html">Requests and Macros</a>.
Control characters are recognized only at the beginning of an input
line, or at the beginning of the branch of a control structure request;
see <a class="ref" href="Conditionals-and-Loops.html">Conditionals and Loops</a>.
</p>
<p>A few requests cause a break implicitly; use the no-break control
character to prevent the break. Break suppression is its sole
behavioral distinction. Employing the no-break control character to
invoke requests that don’t cause breaks is harmless but poor style.
See <a class="xref" href="Manipulating-Filling-and-Adjustment.html">Manipulating Filling and Adjustment</a>.
</p>
<a class="index-entry-id" id="index-control-character_002c-changing-_0028cc_0029"></a>
<a class="index-entry-id" id="index-character_002c-control_002c-changing-_0028cc_0029"></a>
<a class="index-entry-id" id="index-no_002dbreak-control-character_002c-changing-_0028c2_0029"></a>
<a class="index-entry-id" id="index-character_002c-no_002dbreak-control_002c-changing-_0028c2_0029"></a>
<a class="index-entry-id" id="index-control-character_002c-no_002dbreak_002c-changing-_0028c2_0029"></a>
<p>The control ‘<samp class="samp">.</samp>’ and no-break control ‘<samp class="samp">'</samp>’ characters can each
be changed to any ordinary character<a class="footnote" id="DOCF42" href="groff.html_fot.html#FOOT42"><sup>42</sup></a>
with the <code class="code">cc</code> and <code class="code">c2</code> requests, respectively.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002ecc"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.cc</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">o</i></span>]</var><a class="copiable-link" href='#index-_002ecc'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-cc"></a>
<p>Recognize the ordinary character <var class="var">o</var> as the control character.
If <var class="var">o</var> is absent or invalid, the default control character
‘<samp class="samp">.</samp>’ is selected. The identity of the control character is
associated with the environment (see <a class="pxref" href="Environments.html">Environments</a>).
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002ec2"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.c2</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">o</i></span>]</var><a class="copiable-link" href='#index-_002ec2'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-c2"></a>
<p>Recognize the ordinary character <var class="var">o</var> as the no-break control
character. If <var class="var">o</var> is absent or invalid, the default no-break
control character ‘<samp class="samp">'</samp>’ is selected. The identity of the no-break
control character is associated with the environment
(see <a class="pxref" href="Environments.html">Environments</a>).
</p></dd></dl>
<p>When writing a macro, you might wish to know which control character was
used to call it.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cn_005b_002ebr_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.br]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002ebr_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002ebr-1"></a>
<p>This read-only register interpolates 1 if the currently executing
macro was called using the normal control character and 0
otherwise. If a macro is interpolated as a string, the <code class="code">.br</code>
register’s value is inherited from the context of the string
interpolation. See <a class="xref" href="Strings.html">Strings</a>.
</p>
<a class="index-entry-id" id="index-intercepting-requests"></a>
<a class="index-entry-id" id="index-requests_002c-intercepting"></a>
<a class="index-entry-id" id="index-modifying-requests"></a>
<a class="index-entry-id" id="index-requests_002c-modifying"></a>
<p>Use this register to reliably intercept requests that imply breaks.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.als bp*orig bp
.de bp
. ie \\n[.br] .bp*orig
. el 'bp*orig
..
</pre></div></div>
<p>Testing the <code class="code">.br</code> register outside of a macro definition makes no
sense.
</p></dd></dl>
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