diff options
Diffstat (limited to '')
| -rw-r--r-- | doc/groff.html.node/Copy-Mode.html | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/doc/groff.html.node/Copy-Mode.html b/doc/groff.html.node/Copy-Mode.html new file mode 100644 index 0000000..cc7de66 --- /dev/null +++ b/doc/groff.html.node/Copy-Mode.html @@ -0,0 +1,256 @@ +<!DOCTYPE html> +<html> +<!-- Created by GNU Texinfo 7.0.3, https://www.gnu.org/software/texinfo/ --> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> +<!-- This manual documents GNU troff version 1.23.0. + +Copyright © 1994-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A +copy of the license is included in the section entitled "GNU Free +Documentation License". --> +<title>Copy Mode (The GNU Troff Manual)</title> + +<meta name="description" content="Copy Mode (The GNU Troff Manual)"> +<meta name="keywords" content="Copy Mode (The GNU Troff Manual)"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta name="viewport" content="width=device-width,initial-scale=1"> + +<link href="index.html" rel="start" title="Top"> +<link href="Request-Index.html" rel="index" title="Request Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Writing-Macros.html" rel="up" title="Writing Macros"> +<link href="Parameters.html" rel="prev" title="Parameters"> +<style type="text/css"> +<!-- +a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em} +div.example {margin-left: 3.2em} +kbd.key {font-style: normal} +span.r {font-family: initial; font-weight: normal; font-style: normal} +span:hover a.copiable-link {visibility: visible} +strong.def-name {font-family: monospace; font-weight: bold; font-size: larger} +--> +</style> + + +</head> + +<body lang="en"> +<div class="subsection-level-extent" id="Copy-Mode"> +<div class="nav-panel"> +<p> +Previous: <a href="Parameters.html" accesskey="p" rel="prev">Parameters</a>, Up: <a href="Writing-Macros.html" accesskey="u" rel="up">Writing Macros</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> +</div> +<hr> +<h4 class="subsection" id="Copy-Mode-1">5.24.2 Copy Mode</h4> +<a class="index-entry-id" id="index-copy-mode"></a> +<a class="index-entry-id" id="index-copy-mode-1"></a> +<a class="index-entry-id" id="index-mode_002c-copy"></a> +<a class="index-entry-id" id="index-mode_002c-copy-1"></a> + +<a class="index-entry-id" id="index-_005cn_002c-when-reading-text-for-a-macro"></a> +<a class="index-entry-id" id="index-_005c_0024_002c-when-reading-text-for-a-macro"></a> +<a class="index-entry-id" id="index-_005c_002a_002c-when-reading-text-for-a-macro"></a> +<a class="index-entry-id" id="index-_005cRET_002c-when-reading-text-for-a-macro"></a> +<p>When GNU <code class="code">troff</code> processes certain requests, most importantly those +which define or append to a macro or string, it does so in <em class="dfn">copy +mode</em>: it copies the characters of the definition into a dedicated +storage region, interpolating the escape sequences <code class="code">\n</code>, <code class="code">\g</code>, +<code class="code">\$</code>, <code class="code">\*</code>, <code class="code">\V</code>, and <code class="code">\?</code> normally; interpreting +<code class="code">\<kbd class="key">RET</kbd></code> immediately; discarding comments <code class="code">\"</code> and +<code class="code">\#</code>; interpolating the current leader, escape, or tab character +with <code class="code">\a</code>, <code class="code">\e</code>, and <code class="code">\t</code>, respectively; and storing all +other escape sequences in an encoded form. +</p> +<a class="index-entry-id" id="index-interpretation-mode"></a> +<a class="index-entry-id" id="index-mode_002c-interpretation"></a> +<p>The complement of copy mode—a <code class="code">roff</code> formatter’s behavior when +not defining or appending to a macro, string, or diversion—where all +macros are interpolated, requests invoked, and valid escape sequences +processed immediately upon recognition, can be termed +<em class="dfn">interpretation mode</em>. +</p> +<dl class="first-deffn"> +<dt class="deffn" id="index-_005c_005c-1"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\\</code><span class="r"><i class="slanted"></i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005c_005c-1'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-_005c_005c"></a> +<p>The escape character, <code class="code">\</code> by default, can escape itself. This +enables you to control whether a given <code class="code">\n</code>, <code class="code">\g</code>, <code class="code">\$</code>, +<code class="code">\*</code>, <code class="code">\V</code>, or <code class="code">\?</code> escape sequence is interpreted at the +time the macro containing it is defined, or later when the macro is +called.<a class="footnote" id="DOCF101" href="groff.html_fot.html#FOOT101"><sup>101</sup></a> +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.nr x 20 +.de y +.nr x 10 +\&\nx +\&\\nx +.. +.y + ⇒ 20 10 +</pre></div></div> + +<p>You can think of <code class="code">\\</code> as a “delayed” backslash; it is the escape +character followed by a backslash from which the escape character has +removed its special meaning. Consequently, ‘<samp class="samp">\\</samp>’ is not an escape +sequence in the usual sense. In any escape sequence ‘<samp class="samp">\<var class="var">X</var></samp>’ +that GNU <code class="code">troff</code> does not recognize, the escape character is +ignored and <var class="var">X</var> is output. An unrecognized escape sequence causes +a warning in category ‘<samp class="samp">escape</samp>’, with two exceptions—‘<samp class="samp">\\</samp>’ is +the first. +</p></dd></dl> + +<a class="index-entry-id" id="index-_005c_005c_002c-when-reading-text-for-a-macro"></a> +<dl class="first-deffn"> +<dt class="deffn" id="index-_005c_002e-1"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\.</code><span class="r"><i class="slanted"></i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005c_002e-1'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-_005c_002e"></a> +<p><code class="code">\.</code> escapes the control character. It is similar to <code class="code">\\</code> in +that it isn’t a true escape sequence. It is used to permit nested macro +definitions to end without a named macro call to conclude them. Without +a syntax for escaping the control character, this would not be possible. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de m1 +foo +. +. de m2 +bar +\\.. +. +.. +.m1 +.m2 + ⇒ foo bar +</pre></div></div> + +<p>The first backslash is consumed while the macro is read, and the second +is interpreted when macro <code class="code">m1</code> is called. +</p></dd></dl> + +<p><code class="code">roff</code> documents should not use the <code class="code">\\</code> or <code class="code">\.</code> +character sequences outside of copy mode; they serve only to obfuscate +the input. Use <code class="code">\e</code> to represent the escape character, +<code class="code">\[rs]</code> to obtain a backslash glyph, and <code class="code">\&</code> before ‘<samp class="samp">.</samp>’ +and ‘<samp class="samp">'</samp>’ where GNU <code class="code">troff</code> expects them as control characters +if you mean to use them literally (recall <a class="ref" href="Requests-and-Macros.html">Requests and Macros</a>). +</p> +<p>Macro definitions can be nested to arbitrary depth. The mechanics of +parsing the escape character have significant consequences for this +practice. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de M1 +\\$1 +. de M2 +\\\\$1 +. de M3 +\\\\\\\\$1 +\\\\.. +. M3 hand. +\\.. +. M2 of +.. +This understeer is getting +.M1 out + ⇒ This understeer is getting out of hand. +</pre></div></div> + +<p>Each escape character is interpreted twice—once in copy mode, when the +macro is defined, and once in interpretation mode, when the macro is +called. As seen above, this fact leads to exponential growth in the +quantity of escape characters required to delay interpolation of +<code class="code">\n</code>, <code class="code">\g</code>, <code class="code">\$</code>, <code class="code">\*</code>, <code class="code">\V</code>, and <code class="code">\?</code> at +each nesting level, which can be daunting. GNU <code class="code">troff</code> offers a +solution. +</p> +<dl class="first-deffn"> +<dt class="deffn" id="index-_005cE-1"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\E</code><span class="r"><i class="slanted"></i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005cE-1'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-_005cE"></a> +<p><code class="code">\E</code> represents an escape character that is not interpreted in copy +mode. You can use it to ease the writing of nested macro definitions. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de M1 +. nop \E$1 +. de M2 +. nop \E$1 +. de M3 +. nop \E$1 +\\\\.. +. M3 better. +\\.. +. M2 bit +.. +This vehicle handles +.M1 a + ⇒ This vehicle handles a bit better. +</pre></div></div> + +<p>Observe that because <code class="code">\.</code> is not a true escape sequence, we can’t +use <code class="code">\E</code> to keep ‘<samp class="samp">..</samp>’ from ending a macro definition +prematurely. If the multiplicity of backslashes complicates +maintenance, use end macros. +</p> +<p><code class="code">\E</code> is also convenient to define strings containing escape +sequences that need to work when used in copy mode (for example, as +macro arguments), or which will be interpolated at varying macro nesting +depths. We might define strings to begin and end superscripting +as follows.<a class="footnote" id="DOCF102" href="groff.html_fot.html#FOOT102"><sup>102</sup></a> +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.ds { \v'-.9m\s'\En[.s]*7u/10u'+.7m' +.ds } \v'-.7m\s0+.9m' +</pre></div></div> + +<p>When the <code class="code">ec</code> request is used to redefine the escape character, +<code class="code">\E</code> also makes it easier to distinguish the semantics of an escape +character from the other meaning(s) its character might have. Consider +the use of an unusual escape character, ‘<samp class="samp">-</samp>’. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.nr a 1 +.ec - +.de xx +--na +.. +.xx + ⇒ -na +</pre></div></div> + +<p>This result may surprise you; some people expect ‘<samp class="samp">1</samp>’ to be output +since register ‘<samp class="samp">a</samp>’ has clearly been defined with that value. What +has happened? The robotic replacement of ‘<samp class="samp">\</samp>’ with ‘<samp class="samp">-</samp>’ has led +us astray. You might recognize the sequence ‘<samp class="samp">--</samp>’ more readily with +the default escape character as ‘<samp class="samp">\-</samp>’, the special character escape +sequence for the minus sign glyph. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.nr a 1 +.ec - +.de xx +-Ena +.. +.xx + ⇒ 1 +</pre></div></div> +</dd></dl> + + + +</div> +<hr> +<div class="nav-panel"> +<p> +Previous: <a href="Parameters.html">Parameters</a>, Up: <a href="Writing-Macros.html">Writing Macros</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> +</div> + + + +</body> +</html> |