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<title>Built-in Registers (The GNU Troff Manual)</title>
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<div class="subsection-level-extent" id="Built_002din-Registers">
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<p>
Previous: <a href="Assigning-Register-Formats.html" accesskey="p" rel="prev">Assigning Register Formats</a>, Up: <a href="Registers.html" accesskey="u" rel="up">Registers</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Request-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
<h4 class="subsection" id="Built_002din-Registers-1">5.8.5 Built-in Registers</h4>
<a class="index-entry-id" id="index-built_002din-registers"></a>
<a class="index-entry-id" id="index-registers_002c-built_002din"></a>
<p>Predefined registers whose identifiers start with a dot are read-only.
Many are Boolean-valued, interpolating a true or false value testable
with the <code class="code">if</code>, <code class="code">ie</code>, or <code class="code">while</code> requests. Some read-only
registers are string-valued, meaning that they interpolate text.
</p>
<a class="index-entry-id" id="index-removing-a-built_002din-register"></a>
<a class="index-entry-id" id="index-register_002c-built_002din_002c-removing"></a>
<a class="index-entry-id" id="index-built_002din-register_002c-removing"></a>
<p><strong class="strong">Caution:</strong> Built-in registers are subject to removal like
others; once removed, they can be recreated only as normal writable
registers and will not reflect formatter state.
</p>
<p>A register name (without the dot) is often associated with a request of
the same name. A complete listing of all built-in registers can be
found in <a class="ref" href="Register-Index.html">Register Index</a>.
</p>
<p>We present here a few built-in registers that are not described
elsewhere in this manual; they have to do with invariant properties of
GNU <code class="code">troff</code>, or obtain information about the formatter’s
command-line options, processing progress, or the operating environment.
</p>
<dl class="table">
<dt id='index-_002eA'><span><code class="code">\n[.A]</code><a class="copiable-link" href='#index-_002eA'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-approximation-output-register-_0028_002eA_0029"></a>
<a class="index-entry-id" id="index-plain-text-approximation-output-register-_0028_002eA_0029-1"></a>
<p>Approximate output is being formatted (Boolean-valued); see
<code class="command">groff</code> <samp class="option">-a</samp> option (<a class="ref" href="Groff-Options.html">Options</a>).
</p>
</dd>
<dt id='index-c_002e'><span><code class="code">\n[.c]</code><a class="copiable-link" href='#index-c_002e'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002ec"></a>
</dd>
<dt><code class="code">\n[c.]</code></dt>
<dd><a class="index-entry-id" id="index-input-line-number-register-_0028_002ec_002c-c_002e_0029"></a>
<a class="index-entry-id" id="index-line-number_002c-input_002c-register-_0028_002ec_002c-c_002e_0029"></a>
<p>Input line number. ‘<samp class="samp">c.</samp>’ is a writable synonym,
affecting subsequent interpolations of both ‘<samp class="samp">.c</samp>’ and ‘<samp class="samp">c.</samp>’.
</p>
</dd>
<dt id='index-current-input-file-name-register-_0028_002eF_0029'><span><code class="code">\n[.F]</code><a class="copiable-link" href='#index-current-input-file-name-register-_0028_002eF_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-input-file-name_002c-current_002c-register-_0028_002eF_0029"></a>
<a class="index-entry-id" id="index-_002eF"></a>
<p>Name of input file (string-valued).
</p>
</dd>
<dt id='index-_002eg'><span><code class="code">\n[.g]</code><a class="copiable-link" href='#index-_002eg'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-GNU-troff_002c-identification-register-_0028_002eg_0029"></a>
<a class="index-entry-id" id="index-GNU_002dspecific-register-_0028_002eg_0029"></a>
<p>Always true in GNU <code class="code">troff</code> (Boolean-valued). Documents can use
this to ask the formatter if it claims <code class="code">groff</code> compatibility.
</p>
</dd>
<dt id='index-_002eP'><span><code class="code">\n[.P]</code><a class="copiable-link" href='#index-_002eP'> ¶</a></span></dt>
<dd><p>Output page selection status (Boolean-valued); see <code class="command">groff</code>
<samp class="option">-o</samp> option (<a class="ref" href="Groff-Options.html">Options</a>).
</p>
</dd>
<dt id='index-number-of-registers-register-_0028_002eR_0029'><span><code class="code">\n[.R]</code><a class="copiable-link" href='#index-number-of-registers-register-_0028_002eR_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-registers_002c-number-of_002c-register-_0028_002eR_0029"></a>
<a class="index-entry-id" id="index-_002eR-2"></a>
<p>Count of available unused registers; always 10,000 in GNU
<code class="code">troff</code>.<a class="footnote" id="DOCF52" href="groff.html_fot.html#FOOT52"><sup>52</sup></a>
</p>
</dd>
<dt id='index-_002eT-2'><span><code class="code">\n[.T]</code><a class="copiable-link" href='#index-_002eT-2'> ¶</a></span></dt>
<dd><p>Indicator of output device selection (Boolean-valued); see
<code class="command">groff</code> <samp class="option">-T</samp> option (<a class="ref" href="Groff-Options.html">Options</a>).
</p>
</dd>
<dt id='index-safer-mode-2'><span><code class="code">\n[.U]</code><a class="copiable-link" href='#index-safer-mode-2'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-mode_002c-safer-2"></a>
<a class="index-entry-id" id="index-unsafe-mode-2"></a>
<a class="index-entry-id" id="index-mode_002c-unsafe-2"></a>
<a class="index-entry-id" id="index-_002eU"></a>
<p>Unsafe mode enablement status (Boolean-valued); see <code class="command">groff</code>
<samp class="option">-U</samp> option (<a class="ref" href="Groff-Options.html">Options</a>).
</p>
</dd>
<dt id='index-_002ex'><span><code class="code">\n[.x]</code><a class="copiable-link" href='#index-_002ex'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-major-version-number-register-_0028_002ex_0029"></a>
<a class="index-entry-id" id="index-version-number_002c-major_002c-register-_0028_002ex_0029"></a>
<p>Major version number of the running GNU <code class="code">troff</code> formatter. For
example, if the version number is 1.23.0, then <code class="code">.x</code>
contains ‘<samp class="samp">1</samp>’.
</p>
</dd>
<dt id='index-_002ey'><span><code class="code">\n[.y]</code><a class="copiable-link" href='#index-_002ey'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-minor-version-number-register-_0028_002ey_0029"></a>
<a class="index-entry-id" id="index-version-number_002c-minor_002c-register-_0028_002ey_0029"></a>
<p>Minor version number of the running GNU <code class="code">troff</code> formatter. For
example, if the version number is 1.23.0, then <code class="code">.y</code>
contains ‘<samp class="samp">23</samp>’.
</p>
</dd>
<dt id='index-_002eY'><span><code class="code">\n[.Y]</code><a class="copiable-link" href='#index-_002eY'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-revision-number-register-_0028_002eY_0029"></a>
<p>Revision number of the running GNU <code class="code">troff</code> formatter. For example,
if the version number is 1.23.0, then <code class="code">.Y</code> contains ‘<samp class="samp">0</samp>’.
</p>
</dd>
<dt id='index-_0024_0024'><span><code class="code">\n[$$]</code><a class="copiable-link" href='#index-_0024_0024'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-process-ID-of-GNU-troff-register-_0028_0024_0024_0029"></a>
<a class="index-entry-id" id="index-PID-of-GNU-troff-register-_0028_0024_0024_0029"></a>
<a class="index-entry-id" id="index-GNU-troff_002c-process-ID-register-_0028_0024_0024_0029"></a>
<a class="index-entry-id" id="index-GNU-troff_002c-PID-register-_0028_0024_0024_0029"></a>
<p>Process identifier (PID) of the GNU <code class="code">troff</code> program in its
operating environment.
</p></dd>
</dl>
<p>Date- and time-related registers are set per the local time as
determined by <cite class="cite">localtime<span class="r">(3)</span></cite> when the formatter launches. This
initialization can be overridden by <code class="env">SOURCE_DATE_EPOCH</code> and
<code class="env">TZ</code>; see <a class="ref" href="Environment.html">Environment</a>.
</p>
<dl class="table">
<dt id='index-seconds_002c-current-time-_0028seconds_0029'><span><code class="code">\n[seconds]</code><a class="copiable-link" href='#index-seconds_002c-current-time-_0028seconds_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-time_002c-current_002c-seconds-_0028seconds_0029"></a>
<a class="index-entry-id" id="index-current-time_002c-seconds-_0028seconds_0029"></a>
<a class="index-entry-id" id="index-seconds"></a>
<p>Count of seconds elapsed in the minute (0–60). </p>
</dd>
<dt id='index-minutes_002c-current-time-_0028minutes_0029'><span><code class="code">\n[minutes]</code><a class="copiable-link" href='#index-minutes_002c-current-time-_0028minutes_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-time_002c-current_002c-minutes-_0028minutes_0029"></a>
<a class="index-entry-id" id="index-current-time_002c-minutes-_0028minutes_0029"></a>
<a class="index-entry-id" id="index-minutes"></a>
<p>Count of minutes elapsed in the hour (0–59).
</p>
</dd>
<dt id='index-hours_002c-current-time-_0028hours_0029'><span><code class="code">\n[hours]</code><a class="copiable-link" href='#index-hours_002c-current-time-_0028hours_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-time_002c-current_002c-hours-_0028hours_0029"></a>
<a class="index-entry-id" id="index-current-time_002c-hours-_0028hours_0029"></a>
<a class="index-entry-id" id="index-hours"></a>
<p>Count of hours elapsed since midnight (0–23).
</p>
</dd>
<dt id='index-day-of-the-week-register-_0028dw_0029'><span><code class="code">\n[dw]</code><a class="copiable-link" href='#index-day-of-the-week-register-_0028dw_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-date_002c-day-of-the-week-register-_0028dw_0029"></a>
<a class="index-entry-id" id="index-dw"></a>
<p>Day of the week (1–7; 1 is Sunday).
</p>
</dd>
<dt id='index-day-of-the-month-register-_0028dy_0029'><span><code class="code">\n[dy]</code><a class="copiable-link" href='#index-day-of-the-month-register-_0028dy_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-date_002c-day-of-the-month-register-_0028dy_0029"></a>
<a class="index-entry-id" id="index-dy"></a>
<p>Day of the month (1–31).
</p>
</dd>
<dt id='index-month-of-the-year-register-_0028mo_0029'><span><code class="code">\n[mo]</code><a class="copiable-link" href='#index-month-of-the-year-register-_0028mo_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-date_002c-month-of-the-year-register-_0028mo_0029"></a>
<a class="index-entry-id" id="index-mo"></a>
<p>Month of the year (1–12).
</p>
</dd>
<dt id='index-date_002c-year-register-_0028year_002c-yr_0029'><span><code class="code">\n[year]</code><a class="copiable-link" href='#index-date_002c-year-register-_0028year_002c-yr_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-year_002c-current_002c-register-_0028year_002c-yr_0029"></a>
<a class="index-entry-id" id="index-year"></a>
<p>Gregorian year.
</p>
<a class="index-entry-id" id="index-CSTR-_002354-errata"></a>
<a class="index-entry-id" id="index-CSTR-_002354-erratum_002c-yr-register"></a>
</dd>
<dt id='index-yr'><span><code class="code">\n[yr]</code><a class="copiable-link" href='#index-yr'> ¶</a></span></dt>
<dd><p>Gregorian year minus 1900. This register is incorrectly documented
in the <abbr class="acronym">AT&T</abbr> <code class="code">troff</code> manual as storing the last two digits
of the current year. That claim stopped being true in 2000. Old
<code class="code">troff</code> input that looks like:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">'\" The year number is a surprise after 1999.
This document was formatted in 19\n(yr.
</pre></div></div>
<p>can be corrected to:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">This document was formatted in \n[year].
</pre></div></div>
<p>or, for portability across many <code class="code">roff</code> programs, to the following.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.nr y4 1900+\n(yr
This document was formatted in \n(y4.
</pre></div></div>
</dd>
</dl>
</div>
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