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<title>Character Translations (The GNU Troff Manual)</title>
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<div class="section-level-extent" id="Character-Translations">
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<h3 class="section" id="Character-Translations-1">5.13 Character Translations</h3>
<a class="index-entry-id" id="index-character-translations"></a>
<a class="index-entry-id" id="index-translations-of-characters"></a>
<p>A <em class="dfn">translation</em> is a mapping of an input character to an output
glyph. The mapping occurs at output time, i.e., the input character
gets assigned the metric information of the mapped output character
right before input tokens are converted to nodes (see <a class="pxref" href="Gtroff-Internals.html"><code class="code">gtroff</code> Internals</a>, for more on this process).
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002etr"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.tr</code></strong> <var class="def-var-arguments"><span class="r"><i class="slanted">a</i></span><span class="r"><i class="slanted">b</i></span><span class="r"><i class="slanted">c</i></span><span class="r"><i class="slanted">d</i></span>…</var><a class="copiable-link" href='#index-_002etr'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-tr"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_002etrin"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.trin</code></strong> <var class="def-var-arguments"><span class="r"><i class="slanted">a</i></span><span class="r"><i class="slanted">b</i></span><span class="r"><i class="slanted">c</i></span><span class="r"><i class="slanted">d</i></span>…</var><a class="copiable-link" href='#index-_002etrin'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-trin"></a>
<p>Translate character <var class="var">a</var> to glyph <var class="var">b</var>, character <var class="var">c</var> to
glyph <var class="var">d</var>, and so on. If there is an odd number of characters
in the argument, the last one is translated to a fixed-width space (the
same one obtained by the <code class="code">\<kbd class="key">SP</kbd></code> escape sequence).
</p>
<p>The <code class="code">trin</code> request is identical to <code class="code">tr</code>, but when you unformat
a diversion with <code class="code">asciify</code> it ignores the translation.
See <a class="xref" href="Diversions.html">Diversions</a>, for details about the <code class="code">asciify</code> request.
</p>
<p>Some notes:
</p>
<ul class="itemize mark-bullet">
<li><a class="index-entry-id" id="index-_005c_0028_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_005b_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_0027_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_0060_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_002d_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_005f_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005cC_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005cN_002c-and-translations"></a>
<a class="index-entry-id" id="index-char-request_002c-and-translations"></a>
<a class="index-entry-id" id="index-special-characters-1"></a>
<a class="index-entry-id" id="index-character_002c-special"></a>
<a class="index-entry-id" id="index-numbered-glyph-_0028_005cN_0029"></a>
<a class="index-entry-id" id="index-glyph_002c-numbered-_0028_005cN_0029"></a>
Special characters (<code class="code">\(<var class="var">xx</var></code>, <code class="code">\[<var class="var">xxx</var>]</code>,
<code class="code">\C'<var class="var">xxx</var>'</code>, <code class="code">\'</code>, <code class="code">\`</code>, <code class="code">\-</code>, <code class="code">\_</code>),
glyphs defined with the <code class="code">char</code> request, and numbered glyphs
(<code class="code">\N'<var class="var">xxx</var>'</code>) can be translated also.
</li><li><a class="index-entry-id" id="index-_005ce_002c-and-translations"></a>
The <code class="code">\e</code> escape can be translated also.
</li><li><a class="index-entry-id" id="index-_005c_0025_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005c_007e_002c-and-translations"></a>
Characters can be mapped onto the <code class="code">\%</code> and <code class="code">\~</code> escape
sequences (but <code class="code">\%</code> and <code class="code">\~</code> can’t be mapped onto another
glyph).
</li><li><a class="index-entry-id" id="index-backspace-character_002c-and-translations"></a>
<a class="index-entry-id" id="index-character_002c-backspace_002c-and-translations"></a>
<a class="index-entry-id" id="index-leader-character_002c-and-translations"></a>
<a class="index-entry-id" id="index-character_002c-leader_002c-and-translations"></a>
<a class="index-entry-id" id="index-newline-character_002c-and-translations"></a>
<a class="index-entry-id" id="index-character_002c-newline_002c-and-translations"></a>
<a class="index-entry-id" id="index-tab-character_002c-and-translations"></a>
<a class="index-entry-id" id="index-character_002c-tab_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005ca_002c-and-translations"></a>
<a class="index-entry-id" id="index-_005ct_002c-and-translations"></a>
The following characters can’t be translated: space (with one exception,
see below), backspace, newline, leader (and <code class="code">\a</code>), tab (and
<code class="code">\t</code>).
</li><li><a class="index-entry-id" id="index-shc-request_002c-and-translations"></a>
Translations are not considered for finding the soft hyphen character
set with the <code class="code">shc</code> request.
</li><li><a class="index-entry-id" id="index-_005c_0026_002c-and-translations"></a>
The pair ‘<samp class="samp"><var class="var">c</var>\&</samp>’ (an arbitrary character <var class="var">c</var> followed
by the dummy character) maps this character to “nothing”.
<div class="example">
<div class="group"><pre class="example-preformatted">.tr a\&
foo bar
⇒ foo br
</pre></div></div>
<p>Even the space character can be mapped to the dummy character.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.tr aa \&
foo bar
⇒ foobar
</pre></div></div>
<p>As shown in the example, the space character can’t be the first
character/glyph pair as an argument of <code class="code">tr</code>. Additionally, it is
not possible to map the space character to any other glyph; requests
like ‘<samp class="samp">.tr aa x</samp>’<!-- /@w --> undo ‘<samp class="samp">.tr aa \&</samp>’<!-- /@w --> instead.
</p>
<p>If justification is active, lines are justified in spite of the ‘empty’
space character (but there is no minimal distance, i.e., the space
character, between words).
</p>
</li><li>After an output glyph has been constructed (this happens at the moment
immediately before the glyph is appended to an output glyph list, either
by direct output, in a macro, diversion, or string), it is no longer
affected by <code class="code">tr</code>.
</li><li>Translating character to glyphs where one of them or both are undefined
is possible also; <code class="code">tr</code> does not check whether the elements of its
argument exist.
<p>See <a class="xref" href="Gtroff-Internals.html"><code class="code">gtroff</code> Internals</a>.
</p>
</li><li>Without an argument, the <code class="code">tr</code> request is ignored.
</li></ul>
</dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002etrnt"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.trnt</code></strong> <var class="def-var-arguments"><span class="r"><i class="slanted">a</i></span><span class="r"><i class="slanted">b</i></span><span class="r"><i class="slanted">c</i></span><span class="r"><i class="slanted">d</i></span>…</var><a class="copiable-link" href='#index-_002etrnt'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-trnt"></a>
<a class="index-entry-id" id="index-_005c_0021_002c-and-trnt"></a>
<p><code class="code">trnt</code> is the same as the <code class="code">tr</code> request except that the
translations do not apply to text that is transparently throughput into
a diversion with <code class="code">\!</code>. See <a class="xref" href="Diversions.html">Diversions</a>.
</p>
<p>For example,
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.tr ab
.di x
\!.tm a
.di
.x
</pre></div></div>
<p>prints ‘<samp class="samp">b</samp>’ to the standard error stream; if <code class="code">trnt</code> is used
instead of <code class="code">tr</code> it prints ‘<samp class="samp">a</samp>’.
</p></dd></dl>
</div>
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