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<title>End-of-input Traps (The GNU Troff Manual)</title>
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<div class="subsection-level-extent" id="End_002dof_002dinput-Traps">
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<h4 class="subsection" id="End_002dof_002dinput-Traps-1">5.28.5 End-of-input Traps</h4>
<a class="index-entry-id" id="index-end_002dof_002dinput-traps"></a>
<a class="index-entry-id" id="index-traps_002c-end_002dof_002dinput"></a>
<dl class="first-deffn">
<dt class="deffn" id="index-_002eem"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.em</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">name</i></span>]</var><a class="copiable-link" href='#index-_002eem'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-em"></a>
<a class="index-entry-id" id="index-setting-end_002dof_002dinput-trap-_0028em_0029"></a>
<a class="index-entry-id" id="index-end_002dof_002dinput-trap_002c-setting-_0028em_0029"></a>
<a class="index-entry-id" id="index-trap_002c-end_002dof_002dinput_002c-setting-_0028em_0029"></a>
<a class="index-entry-id" id="index-end_002dof_002dinput-macro-_0028em_0029"></a>
<a class="index-entry-id" id="index-macro_002c-end_002dof_002dinput-_0028em_0029"></a>
<p>Set a trap at the end of input, calling macro <var class="var">name</var> after the last
line of the last input file has been processed. If no argument is
given, any existing end-of-input trap is removed.
</p>
<p>For example, if the document had to have a section at the bottom of the
last page for someone to approve it, the <code class="code">em</code> request could be
used.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de approval
\c
. ne 3v
. sp (\\n[.t]u - 3v)
. in +4i
. lc _
. br
Approved:\t\a
. sp
Date:\t\t\a
..
.
.em approval
</pre></div></div>
<p>The <code class="code">\c</code> in the above example needs explanation. For historical
reasons (compatibility with <abbr class="acronym">AT&T</abbr> <code class="code">troff</code>), the
end-of-input macro exits as soon as it causes a page break if no
partially collected line remains.<a class="footnote" id="DOCF111" href="groff.html_fot.html#FOOT111"><sup>111</sup></a>
</p>
<a class="index-entry-id" id="index-page-break_002c-final"></a>
<a class="index-entry-id" id="index-break_002c-page_002c-final"></a>
<a class="index-entry-id" id="index-page-ejection_002c-of-final-page"></a>
<a class="index-entry-id" id="index-ejection_002c-page_002c-of-final-page"></a>
<p>Let us assume that there is no <code class="code">\c</code> in the above <code class="code">approval</code>
macro, that the page is full, and last output line has been broken with,
say, a <code class="code">br</code> request. Because there is no more room, a <code class="code">ne</code>
request at this point causes a page ejection, which in turn makes
<code class="code">troff</code> exit immediately as just described. In most situations,
this is not desired; people generally want to format the input after
<code class="code">ne</code>.
</p>
<p>To force processing of the whole end-of-input macro independently of
this behavior, it is thus advisable to (invisibly) ensure the existence
of a partially collected line (<code class="code">\c</code>) whenever there is a chance
that a page break can happen. In the above example, invoking the
<code class="code">ne</code> request ensures that there is room for the subsequent
formatted output on the same page, so we need insert <code class="code">\c</code> only
once.
</p>
<p>The next example shows how to append three lines, then start a new page
unconditionally. Since ‘<samp class="samp">.ne 1</samp>’<!-- /@w --> doesn’t give the desired
effect—there is always one line available or we are already at the
beginning of the next page—we temporarily increase the page length by
one line so that we can use ‘<samp class="samp">.ne 2</samp>’<!-- /@w -->.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de EM
.pl +1v
\c
.ne 2
line one
.br
\c
.ne 2
line two
.br
\c
.ne 2
line three
.br
.pl -1v
\c
'bp
..
.em EM
</pre></div></div>
<p>This specific feature affects only the first potential page break caused
by the end-of-input macro; further page breaks emitted by the macro are
handled normally.
</p>
<p>Another possible use of the <code class="code">em</code> request is to make GNU
<code class="code">troff</code> emit a single large page instead of multiple pages. For
example, one may want to produce a long plain text file for reading
in a terminal or emulator without page footers and headers interrupting
the body of the document. One approach is to set the page length at the
beginning of the document to a very large value to hold all the
text,<a class="footnote" id="DOCF112" href="groff.html_fot.html#FOOT112"><sup>112</sup></a> and
automatically adjust it to the exact height of the document after the
text has been output.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de adjust-page-length
. br
. pl \\n[nl]u \" \n[nl]: current vertical position
..
.
.de single-page-mode
. pl 99999
. em adjust-page-length
..
.
.\" Activate the above code if configured.
.if \n[do-continuous-rendering] \
. single-page-mode
</pre></div></div>
<p>Since only one end-of-input trap exists and another macro package may
already use it, care must be taken not to break the mechanism. A simple
solution would be to append the above macro to the macro package’s
end-of-input macro using the <code class="code">am</code> request.
</p></dd></dl>
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