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<p>
Previous: <a href="Using-Escape-Sequences.html" accesskey="p" rel="prev">Using Escape Sequences</a>, Up: <a href="Formatter-Instructions.html" accesskey="u" rel="up">Formatter Instructions</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="Delimiters-1">5.6.5 Delimiters</h4>
<a class="index-entry-id" id="index-delimiting-escape-sequence-arguments"></a>
<a class="index-entry-id" id="index-escape-sequence-argument-delimiters"></a>
<a class="index-entry-id" id="index-delimiters_002c-for-escape-sequence-arguments"></a>
<a class="index-entry-id" id="index-arguments_002c-to-escape-sequences_002c-delimiting"></a>
<a class="index-entry-id" id="index-_0027_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_0022_002c-as-delimiter"></a>
<p>Some escape sequences that require parameters use delimiters. The
neutral apostrophe <code class="code">'</code> is a popular choice and shown in this
document. The neutral double quote <code class="code">"</code> is also commonly seen.
Letters, numerals, and leaders can be used. Punctuation characters
are likely better choices, except for those defined as infix operators
in numeric expressions; see below.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">\l'1.5i\[bu]' \" draw 1.5 inches of bullet glyphs
</pre></div></div>
<a class="index-entry-id" id="index-_005c_0025_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cSP_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_007c_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_005e_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_007b_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_007d_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_0027_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_0060_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_002d_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_005f_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_0021_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_003f_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_0029_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_002f_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_002c_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_0026_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_003a_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c_007e_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005c0_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005ca_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cc_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cd_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005ce_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cE_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cp_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cr_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005ct_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_005cu_002c-as-delimiter"></a>
<p>The following escape sequences don’t take arguments and thus are allowed
as delimiters:
<code class="code">\<kbd class="key">SP</kbd></code>, <code class="code">\%</code>, <code class="code">\|</code>, <code class="code">\^</code>, <code class="code">\{</code>,
<code class="code">\}</code>, <code class="code">\'</code>, <code class="code">\`</code>, <code class="code">\-</code>, <code class="code">\_</code>, <code class="code">\!</code>,
<code class="code">\?</code>, <code class="code">\)</code>, <code class="code">\/</code>, <code class="code">\,</code>, <code class="code">\&</code>, <code class="code">\:</code>,
<code class="code">\~</code>, <code class="code">\0</code>, <code class="code">\a</code>, <code class="code">\c</code>, <code class="code">\d</code>, <code class="code">\e</code>,
<code class="code">\E</code>, <code class="code">\p</code>, <code class="code">\r</code>, <code class="code">\t</code>, and <code class="code">\u</code>. However,
using them this way is discouraged; they can make the input confusing to
read.
</p>
<a class="index-entry-id" id="index-_005cA_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cb_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005co_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cw_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cX_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cZ_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-newline_002c-as-delimiter"></a>
<p>A few escape sequences,
<code class="code">\A</code>,
<code class="code">\b</code>,
<code class="code">\o</code>,
<code class="code">\w</code>,
<code class="code">\X</code>,
and <code class="code">\Z</code>, accept a newline as a delimiter. Newlines that serve
as delimiters continue to be recognized as input line terminators.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">A caf\o
e\(aa
in Paris
⇒ A caf� in Paris
</pre></div></div>
<p>Use of newlines as delimiters in escape sequences is also discouraged.
</p>
<a class="index-entry-id" id="index-_005cD_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005ch_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cH_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cl_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cL_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cN_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cR_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cs_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cS_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cv_002c-delimiters-allowed-by"></a>
<a class="index-entry-id" id="index-_005cx_002c-delimiters-allowed-by"></a>
<p>Finally, the escape sequences <code class="code">\D</code>, <code class="code">\h</code>, <code class="code">\H</code>,
<code class="code">\l</code>, <code class="code">\L</code>, <code class="code">\N</code>, <code class="code">\R</code>, <code class="code">\s</code>, <code class="code">\S</code>,
<code class="code">\v</code>, and <code class="code">\x</code> prohibit many delimiters.
</p>
<ul class="itemize mark-bullet">
<li><a class="index-entry-id" id="index-numerals_002c-as-delimiters"></a>
<a class="index-entry-id" id="index-digits_002c-as-delimiters"></a>
<a class="index-entry-id" id="index-_002e_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-decimal-point_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-dot_002c-as-delimiter"></a>
the numerals <code class="code">0</code>-<code class="code">9</code> and the decimal point <code class="code">.</code>
</li><li><a class="index-entry-id" id="index-operators_002c-as-delimiters"></a>
<a class="index-entry-id" id="index-_002b_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_002d_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_002f_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_002a_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_0025_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_003c_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_003e_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_003d_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_0026_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_003a_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_0028_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-_0029_002c-as-delimiter"></a>
the (single-character) operators ‘<samp class="samp">+-/*%<>=&:()</samp>’
</li><li><a class="index-entry-id" id="index-space-character_002c-as-delimiter"></a>
<a class="index-entry-id" id="index-tab-character_002c-as-delimiter"></a>
the space and tab characters
</li><li><a class="index-entry-id" id="index-_005c_0025_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_003a_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_007b_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_007d_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_0027_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_0060_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_002d_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_005f_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_0021_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005c_002f_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005cc_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005ce_002c-as-delimiter-1"></a>
<a class="index-entry-id" id="index-_005cp_002c-as-delimiter-1"></a>
any escape sequences other than <code class="code">\%</code>, <code class="code">\:</code>, <code class="code">\{</code>,
<code class="code">\}</code>, <code class="code">\'</code>, <code class="code">\`</code>, <code class="code">\-</code>, <code class="code">\_</code>, <code class="code">\!</code>,
<code class="code">\/</code>, <code class="code">\c</code>, <code class="code">\e</code>, and <code class="code">\p</code>
</li></ul>
<p>Delimiter syntax is complex and flexible primarily for historical
reasons; the foregoing restrictions need be kept in mind mainly when
using <code class="code">groff</code> in <abbr class="acronym">AT&T</abbr> compatibility mode. GNU
<code class="code">troff</code> keeps track of the nesting depth of escape sequence
interpolations, so the only characters you need to avoid using as
delimiters are those that appear in the arguments you input, not any
that result from interpolation. Typically, <code class="code">'</code> works fine.
See <a class="xref" href="Implementation-Differences.html">Implementation Differences</a>.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">$ groff -Tps
.de Mw
. nr wd \w'\\$1'
. tm "\\$1" is \\n(wd units wide.
..
.Mw Wet'suwet'en
.Mw Wet+200i
.cp 1 \" turn on compatibility mode
.Mw Wet'suwet'en
.Mw Wet'
.Mw Wet+200i
error→ "Wet'suwet'en" is 54740 units wide.
error→ "Wet'+200i" is 42610 units wide.
error→ "Wet'suwet'en" is 15860 units wide.
error→ "Wet'" is 15860 units wide.
error→ "Wet'+200i" is 14415860 units wide.
</pre></div></div>
<p>We see here that in compatibility mode, the part of the argument after
the <code class="code">'</code> delimiter escapes from its context and, if nefariously
crafted, influences the computation of the <var class="var">wd</var> register’s value in
a surprising way.
</p>
</div>
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