134 lines
5.7 KiB
HTML
134 lines
5.7 KiB
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<!DOCTYPE html>
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>getopt-long Example (Guile Reference Manual)</title>
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<meta name="description" content="getopt-long Example (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="getopt_002dlong.html" rel="up" title="getopt-long">
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<link href="Option-Specification.html" rel="next" title="Option Specification">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="getopt_002dlong-Example">
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<div class="nav-panel">
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<p>
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Next: <a href="Option-Specification.html" accesskey="n" rel="next">How to Write an Option Specification</a>, Up: <a href="getopt_002dlong.html" accesskey="u" rel="up">The (ice-9 getopt-long) Module</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="A-Short-getopt_002dlong-Example"><span>7.4.1 A Short getopt-long Example<a class="copiable-link" href="#A-Short-getopt_002dlong-Example"> ¶</a></span></h4>
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<p>This section illustrates how <code class="code">getopt-long</code> is used by presenting
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and dissecting a simple example. The first thing that we need is an
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<em class="dfn">option specification</em> that tells <code class="code">getopt-long</code> how to parse
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the command line. This specification is an association list with the
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long option name as the key. Here is how such a specification might
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look:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define option-spec
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'((version (single-char #\v) (value #f))
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(help (single-char #\h) (value #f))))
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</pre></div>
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<p>This alist tells <code class="code">getopt-long</code> that it should accept two long
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options, called <em class="emph">version</em> and <em class="emph">help</em>, and that these options
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can also be selected by the single-letter abbreviations <em class="emph">v</em> and
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<em class="emph">h</em>, respectively. The <code class="code">(value #f)</code> clauses indicate that
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neither of the options accepts a value.
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</p>
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<p>With this specification we can use <code class="code">getopt-long</code> to parse a given
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command line:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define options (getopt-long (command-line) option-spec))
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</pre></div>
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<p>After this call, <code class="code">options</code> contains the parsed command line and is
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ready to be examined by <code class="code">option-ref</code>. <code class="code">option-ref</code> is called
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like this:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(option-ref options 'help #f)
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</pre></div>
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<p>It expects the parsed command line, a symbol indicating the option to
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examine, and a default value. The default value is returned if the
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option was not present in the command line, or if the option was present
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but without a value; otherwise the value from the command line is
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returned. Usually <code class="code">option-ref</code> is called once for each possible
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option that a script supports.
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</p>
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<p>The following example shows a main program which puts all this together
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to parse its command line and figure out what the user wanted.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define (main args)
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(let* ((option-spec '((version (single-char #\v) (value #f))
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(help (single-char #\h) (value #f))))
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(options (getopt-long args option-spec))
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(help-wanted (option-ref options 'help #f))
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(version-wanted (option-ref options 'version #f)))
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(if (or version-wanted help-wanted)
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(begin
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(if version-wanted
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(display "getopt-long-example version 0.3\n"))
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(if help-wanted
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(display "\
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getopt-long-example [options]
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-v, --version Display version
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-h, --help Display this help
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")))
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(begin
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(display "Hello, World!") (newline)))))
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</pre></div>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Option-Specification.html">How to Write an Option Specification</a>, Up: <a href="getopt_002dlong.html">The (ice-9 getopt-long) Module</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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