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<title>Tabs and Fields (The GNU Troff Manual)</title>
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<h3 class="section" id="Tabs-and-Fields-1">5.12 Tabs and Fields</h3>
<a class="index-entry-id" id="index-tabs_002c-and-fields"></a>
<a class="index-entry-id" id="index-fields_002c-and-tabs"></a>
<a class="index-entry-id" id="index-tab-character-encoding"></a>
<p>A tab character (<abbr class="acronym">ISO</abbr> code point 9, <abbr class="acronym">EBCDIC</abbr>
code point 5) causes a horizontal movement to the next tab stop, if
any.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005ct-1"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\t</code><span class="r"><i class="slanted"></i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005ct-1'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005ct"></a>
<a class="index-entry-id" id="index-tab-character_002c-non_002dinterpreted-_0028_005ct_0029"></a>
<a class="index-entry-id" id="index-character_002c-tab_002c-non_002dinterpreted-_0028_005ct_0029"></a>
<a class="index-entry-id" id="index-_005ct_002c-and-copy-mode"></a>
<a class="index-entry-id" id="index-copy-mode_002c-and-_005ct"></a>
<a class="index-entry-id" id="index-mode_002c-copy_002c-and-_005ct"></a>
<p>Interpolate a tab in copy mode; see <a class="ref" href="Copy-Mode.html">Copy Mode</a>.
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002eta"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.ta</code></strong> <var class="def-var-arguments">[[<span class="r"><i class="slanted">n1</i></span> <span class="r"><i class="slanted">n2</i></span> … <span class="r"><i class="slanted">nn</i></span> ]<code class="t">T</code> <span class="r"><i class="slanted">r1</i></span> <span class="r"><i class="slanted">r2</i></span> … <span class="r"><i class="slanted">rn</i></span>]</var><a class="copiable-link" href='#index-_002eta'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-ta"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_005b_002etabs_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.tabs]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002etabs_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002etabs"></a>
<p>Change tab stop positions. This request takes a series of tab
specifiers as arguments (optionally divided into two groups with the
letter ‘<samp class="samp">T</samp>’) that indicate where each tab stop is to be, overriding
any previous settings. The default scaling unit is ‘<samp class="samp">m</samp>’. Invoking
<code class="code">ta</code> without an argument removes all tab stops.
<a class="index-entry-id" id="index-default-tab-stops"></a>
<a class="index-entry-id" id="index-tab-stops_002c-default"></a>
GNU <code class="code">troff</code>’s startup value is ‘<samp class="samp">T 0.5i</samp>’<!-- /@w -->.
</p>
<p>Tab stops can be specified absolutely—as distances from the left
margin. The following example sets six tab stops, one every inch.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ta 1i 2i 3i 4i 5i 6i
</pre></div></div>
<p>Tab stops can also be specified using a leading ‘<samp class="samp">+</samp>’, which means
that the specified tab stop is set relative to the previous tab stop.
For example, the following is equivalent to the previous example.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ta 1i +1i +1i +1i +1i +1i
</pre></div></div>
<p>GNU <code class="code">troff</code> supports an extended syntax to specify repeating tab
stops. These stops appear after a ‘<samp class="samp">T</samp>’ argument. Their values are
always taken as distances relative to the previous tab stop. This is
the idiomatic way to specify tab stops at equal intervals in
<code class="code">groff</code>. The following is, yet again, the same as the previous
examples. It does more, in fact, since it defines an infinite number of
tab stops at one-inch intervals.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ta T 1i
</pre></div></div>
<p>Now we are ready to interpret the full syntax given above. The
<code class="code">ta</code> request sets tabs at positions <var class="var">n1</var>, <var class="var">n2</var>, …,
<var class="var">nn</var>, then at <var class="var">nn</var>+<var class="var">r1</var>, <var class="var">nn</var>+<var class="var">r2</var>, …,
<var class="var">nn</var>+<var class="var">rn</var>, then at <var class="var">nn</var>+<var class="var">rn</var>+<var class="var">r1</var>,
<var class="var">nn</var>+<var class="var">rn</var>+<var class="var">r2</var>, …, <var class="var">nn</var>+<var class="var">rn</var>+<var class="var">rn</var>, and so
on.
</p>
<p>For example, ‘<samp class="samp">4c +6c T 3c 5c 2c</samp>’ is equivalent to ‘<samp class="samp">4c 10c 13c
18c 20c 23c 28c 30c …</samp>’.
</p>
<p>Text written to a tab column (i.e., between two tab stops, or between a
tab stop and an output line boundary) may be aligned to the right or
left, or centered in the column. This alignment is determined by
appending ‘<samp class="samp">R</samp>’, ‘<samp class="samp">L</samp>’, or ‘<samp class="samp">C</samp>’ to the tab specifier. The
default is ‘<samp class="samp">L</samp>’.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ta 1i 2iC 3iR
</pre></div></div>
<p>The beginning of an output line is not a tab stop; the text that begins
an output line is placed according to the configured alignment and
indentation; see <a class="ref" href="Manipulating-Filling-and-Adjustment.html">Manipulating Filling and Adjustment</a> and <a class="ref" href="Line-Layout.html">Line Layout</a>.
</p>
<p>A tab stop is converted into a non-breakable horizontal movement that
cannot be adjusted.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ll 2i
.ds foo a\tb\tc
.ta T 1i
\*[foo]
error→ warning: cannot break line
⇒ a b c
</pre></div></div>
<p>The above creates a single output line that is a bit longer than two
inches (we use a string to show exactly where the tab stops are).
Now consider the following.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ll 2i
.ds bar a\tb c\td
.ta T 1i
\*[bar]
error→ warning: cannot adjust line
⇒ a b
⇒ c d
</pre></div></div>
<p>GNU <code class="code">troff</code> first converts the line’s tab stops into unbreakable
horizontal movements, then breaks after ‘<samp class="samp">b</samp>’. This usually isn’t
what you want.
</p>
<p>Superfluous tab characters—those that do not correspond to a tab
stop—are ignored except for the first, which delimits the characters
belonging to the last tab stop for right-alignment or centering.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ds Z foo\tbar\tbaz
.ds ZZ foo\tbar\tbazqux
.ds ZZZ foo\tbar\tbaz\tqux
.ta 2i 4iR
\*[Z]
.br
\*[ZZ]
.br
\*[ZZZ]
.br
⇒ foo bar baz
⇒ foo bar bazqux
⇒ foo bar bazqux
</pre></div></div>
<p>The first line right-aligns “baz” within the second tab stop. The
second line right-aligns “bazqux” within it. The third line
right-aligns only “baz” because of the additional tab character, which
marks the end of the text occupying the last tab stop defined.
</p>
<p>Tab stops are associated with the environment (see <a class="pxref" href="Environments.html">Environments</a>).
</p>
<a class="index-entry-id" id="index-tab-stop-settings-register-_0028_002etabs_0029"></a>
<a class="index-entry-id" id="index-_002eS-register_002c-Plan-9-alias-for-_002etabs"></a>
<a class="index-entry-id" id="index-_002etabs-register_002c-Plan-9-alias-_0028_002eS_0029"></a>
<p>The read-only register <code class="code">.tabs</code> contains a string
representation of the current tab settings suitable for use as an
argument to the <code class="code">ta</code> request.<a class="footnote" id="DOCF66" href="groff.html_fot.html#FOOT66"><sup>66</sup></a>
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.ds tab-string \n[.tabs]
\*[tab-string]
⇒ T120u
</pre></div></div>
</dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002etc"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.tc</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">c</i></span>]</var><a class="copiable-link" href='#index-_002etc'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-tc"></a>
<a class="index-entry-id" id="index-tab-repetition-character-_0028tc_0029"></a>
<a class="index-entry-id" id="index-character_002c-tab-repetition-_0028tc_0029"></a>
<a class="index-entry-id" id="index-glyph_002c-tab-repetition-_0028tc_0029"></a>
<p>Set the tab repetition character to the ordinary or special character
<var class="var">c</var>; normally, no glyph is written when moving to a tab stop (and
some output devices may output space characters to achieve this motion).
A <em class="dfn">tab repetition character</em> causes the formatter to write as many
instances of <var class="var">c</var> as are necessary to occupy the interval from the
horizontal drawing position to the next tab stop. With no argument, GNU
<code class="code">troff</code> reverts to the default behavior. The tab repetition
character is associated with the environment (see <a class="pxref" href="Environments.html">Environments</a>).
Only a single character of <var class="var">c</var> is recognized; any excess is ignored.
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002elinetabs"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.linetabs</code></strong> <var class="def-var-arguments">n</var><a class="copiable-link" href='#index-_002elinetabs'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-linetabs"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_005b_002elinetabs_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.linetabs]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002elinetabs_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002elinetabs-1"></a>
<a class="index-entry-id" id="index-tab_002c-line_002dtabs-mode"></a>
<a class="index-entry-id" id="index-line_002dtabs-mode"></a>
<a class="index-entry-id" id="index-mode_002c-line_002dtabs"></a>
<p>If <var class="var">n</var> is missing or non-zero, activate <em class="dfn">line-tabs</em>; deactivate
it otherwise (the default). Active line-tabs cause GNU <code class="code">troff</code>
to compute tab distances relative to the start of the output line
instead of the input line.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de Tabs
. ds x a\t\c
. ds y b\t\c
. ds z c
. ta 1i 3i
\\*x
\\*y
\\*z
..
.Tabs
.br
.linetabs
.Tabs
⇒ a b c
⇒ a b c
</pre></div></div>
<p>Line-tabs activation is associated with the environment
(see <a class="pxref" href="Environments.html">Environments</a>). The read-only register <code class="code">.linetabs</code>
interpolates 1 if line-tabs are active, and 0 otherwise.
</p></dd></dl>
<ul class="mini-toc">
<li><a href="Leaders.html" accesskey="1">Leaders</a></li>
<li><a href="Fields.html" accesskey="2">Fields</a></li>
</ul>
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