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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:44:05 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:44:05 +0000 |
| commit | d318611dd6f23fcfedd50e9b9e24620b102ba96a (patch) | |
| tree | 8b9eef82ca40fdd5a8deeabf07572074c236095d /doc/groff.html.node/while.html | |
| parent | Initial commit. (diff) | |
| download | groff-upstream/1.23.0.tar.xz groff-upstream/1.23.0.zip | |
Adding upstream version 1.23.0.upstream/1.23.0upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
| -rw-r--r-- | doc/groff.html.node/while.html | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/doc/groff.html.node/while.html b/doc/groff.html.node/while.html new file mode 100644 index 0000000..f9a0bae --- /dev/null +++ b/doc/groff.html.node/while.html @@ -0,0 +1,161 @@ +<!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>while (The GNU Troff Manual)</title> + +<meta name="description" content="while (The GNU Troff Manual)"> +<meta name="keywords" content="while (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="Conditionals-and-Loops.html" rel="up" title="Conditionals and Loops"> +<link href="if_002delse.html" rel="prev" title="if-else"> +<style type="text/css"> +<!-- +a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em} +div.example {margin-left: 3.2em} +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="while"> +<div class="nav-panel"> +<p> +Previous: <a href="if_002delse.html" accesskey="p" rel="prev">if-else</a>, Up: <a href="Conditionals-and-Loops.html" accesskey="u" rel="up">Conditionals and Loops</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="while-1">5.23.5 while</h4> +<a class="index-entry-id" id="index-while"></a> + +<p><code class="code">groff</code> provides a looping construct: the <code class="code">while</code> request. +Its syntax matches the <code class="code">if</code> request. +</p> +<a class="index-entry-id" id="index-body_002c-of-a-while-request"></a> +<dl class="first-deffn"> +<dt class="deffn" id="index-_002ewhile"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.while</code></strong> <var class="def-var-arguments">cond-expr anything</var><a class="copiable-link" href='#index-_002ewhile'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-while-1"></a> +<p>Evaluate the conditional expression <var class="var">cond-expr</var>, and repeatedly +execute <var class="var">anything</var> unless and until <var class="var">cond-expr</var> evaluates false. +<var class="var">anything</var>, which is often a conditional block, is referred to as +the <code class="code">while</code> request’s <em class="dfn">body</em>. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.nr a 0 1 +.while (\na < 9) \{\ +\n+a, +.\} +\n+a + ⇒ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 +</pre></div></div> + +<a class="index-entry-id" id="index-de-request_002c-and-while"></a> +<p>GNU <code class="code">troff</code> treats the body of a <code class="code">while</code> request similarly to +that of a <code class="code">de</code> request (albeit one not read in copy +mode<a class="footnote" id="DOCF94" href="groff.html_fot.html#FOOT94"><sup>94</sup></a>), but stores it under an internal name +and deletes it when the loop finishes. The operation of a macro +containing a <code class="code">while</code> request can slow significantly if the +<code class="code">while</code> body is large. Each time the macro is executed, the +<code class="code">while</code> body is parsed and stored again. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de xxx +. nr num 10 +. while (\\n[num] > 0) \{\ +. \" many lines of code +. nr num -1 +. \} +.. +</pre></div></div> + +<a class="index-entry-id" id="index-recursive-macros"></a> +<a class="index-entry-id" id="index-macros_002c-recursive"></a> +<p>An often better solution—and one that is more portable, since +<abbr class="acronym">AT&T</abbr> <code class="code">troff</code> lacked the <code class="code">while</code> request—is to +instead write a recursive macro. It will be parsed only +once.<a class="footnote" id="DOCF95" href="groff.html_fot.html#FOOT95"><sup>95</sup></a> +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de yyy +. if (\\n[num] > 0) \{\ +. \" many lines of code +. nr num -1 +. yyy +. \} +.. +. +.de xxx +. nr num 10 +. yyy +.. +</pre></div></div> + +<p>To prevent infinite loops, the default number of available recursion +levels is 1,000 or somewhat less.<a class="footnote" id="DOCF96" href="groff.html_fot.html#FOOT96"><sup>96</sup></a> You can +disable this protective measure, or raise the limit, by setting the +<code class="code">slimit</code> register. See <a class="xref" href="Debugging.html">Debugging</a>. +</p> +<p>As noted above, if a <code class="code">while</code> body begins with a conditional block, +its closing brace must end an input line. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.if 1 \{\ +. nr a 0 1 +. while (\n[a] < 10) \{\ +. nop \n+[a] +.\}\} + error→ unbalanced brace escape sequences +</pre></div></div> +</dd></dl> + +<dl class="first-deffn"> +<dt class="deffn" id="index-_002ebreak"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.break</code></strong><a class="copiable-link" href='#index-_002ebreak'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-break-2"></a> +<a class="index-entry-id" id="index-while-request_002c-confusing-with-br"></a> +<a class="index-entry-id" id="index-break-request_002c-in-a-while-loop"></a> +<a class="index-entry-id" id="index-continue-request_002c-in-a-while-loop"></a> +<p>Exit a <code class="code">while</code> loop. Do not confuse this request with a +typographical break or the <code class="code">br</code> request. +</p></dd></dl> + +<dl class="first-deffn"> +<dt class="deffn" id="index-_002econtinue"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.continue</code></strong><a class="copiable-link" href='#index-_002econtinue'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-continue"></a> +<p>Skip the remainder of a <code class="code">while</code> loop’s body, immediately starting +the next iteration. +</p></dd></dl> + + + +</div> +<hr> +<div class="nav-panel"> +<p> +Previous: <a href="if_002delse.html">if-else</a>, Up: <a href="Conditionals-and-Loops.html">Conditionals and Loops</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> |