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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Create an `Arg` from a usage string."><meta name="keywords" content="rust, rustlang, rust-lang, arg"><title>arg in clap - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../dark.css" disabled><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.svg"></head><body class="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../clap/index.html"><div class="logo-container"><img src="https://raw.githubusercontent.com/clap-rs/clap/master/assets/clap.png" alt="logo"></div></a><h2 class="location"></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../clap/index.html"><div class="logo-container">
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<img src="https://raw.githubusercontent.com/clap-rs/clap/master/assets/clap.png" alt="logo"></div></a><div class="sidebar-elems"><h2 class="location"><a href="index.html">In clap</a></h2></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../clap/index.html">
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<img src="https://raw.githubusercontent.com/clap-rs/clap/master/assets/clap.png" alt="logo"></a><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><button type="button">?</button></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav></div><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn"><span class="in-band">Macro <a href="index.html">clap</a>::<wbr><a class="macro" href="#">arg</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span></h1><span class="out-of-band"><a class="srclink" href="../src/clap/macros.rs.html#538-551">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="docblock item-decl"><div class="example-wrap"><pre class="rust macro"><code><span class="macro">macro_rules!</span> <span class="ident">arg</span> {
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( <span class="macro-nonterminal">$</span><span class="macro-nonterminal">name</span>:<span class="ident">ident</span>: $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tail</span>:<span class="ident">tt</span>)<span class="op">+</span> ) => { ... };
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( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tail</span>:<span class="ident">tt</span>)<span class="op">+</span> ) => { ... };
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}</code></pre></div>
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</div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Create an <a href="builder/struct.Arg.html"><code>Arg</code></a> from a usage string.</p>
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<p>Allows creation of basic settings for the <a href="builder/struct.Arg.html"><code>Arg</code></a>.</p>
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<p><strong>NOTE</strong>: Not all settings may be set using the usage string method. Some properties are
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only available via the builder pattern.</p>
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<h2 id="syntax"><a href="#syntax">Syntax</a></h2>
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<p>Usage strings typically following the form:</p>
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<div class="example-wrap"><pre class="language-notrust"><code>[explicit name] [short] [long] [value names] [...] [help string]</code></pre></div><h4 id="explicit-name"><a href="#explicit-name">Explicit Name</a></h4>
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<p>The name may be either a bare-word or a string, followed by a <code>:</code>, like <code>name:</code> or
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<code>"name":</code>.</p>
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<p><em>Note:</em> This is an optional field, if it’s omitted the argument will use one of the additional
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fields as the name using the following priority order:</p>
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<ol>
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<li>Explicit Name</li>
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<li>Long</li>
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<li>Value Name</li>
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</ol>
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<p>See <a href="builder/struct.Arg.html#method.id" title="crate::Arg::id"><code>Arg::id</code></a>.</p>
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<h4 id="short"><a href="#short">Short</a></h4>
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<p>A short flag is a <code>-</code> followed by either a bare-character or quoted character, like <code>-f</code> or
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<code>-'f'</code>.</p>
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<p>See <a href="builder/struct.Arg.html#method.short" title="crate::Arg::short"><code>Arg::short</code></a>.</p>
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<h4 id="long"><a href="#long">Long</a></h4>
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<p>A long flag is a <code>--</code> followed by either a bare-word or a string, like <code>--foo</code> or
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<code>--"foo"</code>.</p>
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<p><strong>NOTE:</strong> Dashes in the long name (e.g. <code>--foo-bar</code>) is not supported and quoting is required
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(e.g. <code>--"foo-bar"</code>).</p>
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<p>See <a href="builder/struct.Arg.html#method.long" title="crate::Arg::long"><code>Arg::long</code></a>.</p>
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<h4 id="values-value-notation"><a href="#values-value-notation">Values (Value Notation)</a></h4>
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<p>This is set by placing bare-word between:</p>
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<ul>
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<li><code>[]</code> like <code>[FOO]</code>
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<ul>
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<li>Positional argument: optional</li>
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<li>Named argument: optional value</li>
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</ul>
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</li>
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<li><code><></code> like <code><FOO></code>: required</li>
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</ul>
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<p>See <a href="builder/struct.Arg.html#method.value_name" title="crate::Arg::value_name"><code>Arg::value_name</code></a>.</p>
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<h4 id=""><a href="#"><code>...</code></a></h4>
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<p><code>...</code> (three consecutive dots/periods) specifies that this argument may occur multiple
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times (not to be confused with multiple values per occurrence).</p>
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<p>See <a href="builder/enum.ArgAction.html#variant.Count" title="crate::ArgAction::Count"><code>ArgAction::Count</code></a> and <a href="builder/enum.ArgAction.html#variant.Append" title="crate::ArgAction::Append"><code>ArgAction::Append</code></a>.</p>
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<h4 id="help-string"><a href="#help-string">Help String</a></h4>
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<p>The help string is denoted between a pair of double quotes <code>""</code> and may contain any
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characters.</p>
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<h2 id="examples"><a href="#examples">Examples</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let</span> <span class="ident">cmd</span> <span class="op">=</span> <span class="ident">Command::new</span>(<span class="string">"prog"</span>)
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.<span class="ident">args</span>(<span class="kw-2">&</span>[
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<span class="macro">arg!</span>(<span class="op">-</span><span class="op">-</span><span class="ident">config</span> <span class="op"><</span><span class="ident">FILE</span><span class="op">></span> <span class="string">"a required file for the configuration and no short"</span>),
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<span class="macro">arg!</span>(<span class="op">-</span><span class="ident">d</span> <span class="op">-</span><span class="op">-</span><span class="ident">debug</span> ... <span class="string">"turns on debugging information and allows multiples"</span>),
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<span class="macro">arg!</span>([<span class="ident">input</span>] <span class="string">"an optional input file to use"</span>)
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]);
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<span class="kw">let</span> <span class="ident">m</span> <span class="op">=</span> <span class="ident">cmd</span>.<span class="ident">try_get_matches_from</span>([<span class="string">"prog"</span>, <span class="string">"--config"</span>, <span class="string">"file.toml"</span>]).<span class="ident">unwrap</span>();
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<span class="macro">assert_eq!</span>(<span class="ident">m</span>.<span class="ident">get_one</span>::<span class="op"><</span><span class="ident">String</span><span class="op">></span>(<span class="string">"config"</span>).<span class="ident">unwrap</span>(), <span class="string">"file.toml"</span>);
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<span class="macro">assert_eq!</span>(<span class="kw-2">*</span><span class="ident">m</span>.<span class="ident">get_one</span>::<span class="op"><</span><span class="ident">u8</span><span class="op">></span>(<span class="string">"debug"</span>).<span class="ident">unwrap</span>(), <span class="number">0</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">m</span>.<span class="ident">get_one</span>::<span class="op"><</span><span class="ident">String</span><span class="op">></span>(<span class="string">"input"</span>), <span class="prelude-val">None</span>);</code></pre></div>
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