mirror of
https://github.com/Dhghomon/easy_rust
synced 2024-11-03 15:40:22 +00:00
459 lines
29 KiB
HTML
459 lines
29 KiB
HTML
<!DOCTYPE HTML>
|
|
<html lang="en" class="sidebar-visible no-js light">
|
|
<head>
|
|
<!-- Book generated using mdBook -->
|
|
<meta charset="UTF-8">
|
|
<title> Taking user input - Easy Rust</title>
|
|
|
|
|
|
|
|
|
|
<!-- Custom HTML head -->
|
|
|
|
|
|
|
|
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
|
<meta name="description" content="">
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|
<meta name="theme-color" content="#ffffff" />
|
|
|
|
|
|
<link rel="icon" href="favicon.svg">
|
|
|
|
|
|
<link rel="shortcut icon" href="favicon.png">
|
|
|
|
<link rel="stylesheet" href="css/variables.css">
|
|
<link rel="stylesheet" href="css/general.css">
|
|
<link rel="stylesheet" href="css/chrome.css">
|
|
|
|
<link rel="stylesheet" href="css/print.css" media="print">
|
|
|
|
|
|
<!-- Fonts -->
|
|
<link rel="stylesheet" href="FontAwesome/css/font-awesome.css">
|
|
|
|
<link rel="stylesheet" href="fonts/fonts.css">
|
|
|
|
|
|
<!-- Highlight.js Stylesheets -->
|
|
<link rel="stylesheet" href="highlight.css">
|
|
<link rel="stylesheet" href="tomorrow-night.css">
|
|
<link rel="stylesheet" href="ayu-highlight.css">
|
|
|
|
<!-- Custom theme stylesheets -->
|
|
|
|
|
|
|
|
</head>
|
|
<body>
|
|
<!-- Provide site root to javascript -->
|
|
<script type="text/javascript">
|
|
var path_to_root = "";
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
|
</script>
|
|
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|
<script type="text/javascript">
|
|
try {
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|
var sidebar = localStorage.getItem('mdbook-sidebar');
|
|
|
|
if (theme.startsWith('"') && theme.endsWith('"')) {
|
|
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
|
}
|
|
|
|
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
|
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
|
}
|
|
} catch (e) { }
|
|
</script>
|
|
|
|
<!-- Set the theme before any content is loaded, prevents flash -->
|
|
<script type="text/javascript">
|
|
var theme;
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
|
if (theme === null || theme === undefined) { theme = default_theme; }
|
|
var html = document.querySelector('html');
|
|
html.classList.remove('no-js')
|
|
html.classList.remove('light')
|
|
html.classList.add(theme);
|
|
html.classList.add('js');
|
|
</script>
|
|
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|
<script type="text/javascript">
|
|
var html = document.querySelector('html');
|
|
var sidebar = 'hidden';
|
|
if (document.body.clientWidth >= 1080) {
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
|
sidebar = sidebar || 'visible';
|
|
}
|
|
html.classList.remove('sidebar-visible');
|
|
html.classList.add("sidebar-" + sidebar);
|
|
</script>
|
|
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
|
<div class="sidebar-scrollbox">
|
|
<ol class="chapter"><li class="chapter-item expanded "><a href="Chapter_0.html"><strong aria-hidden="true">1.</strong> Update</a></li><li class="chapter-item expanded "><a href="Chapter_1.html"><strong aria-hidden="true">2.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="Chapter_2.html"><strong aria-hidden="true">3.</strong> Who am I?</a></li><li class="chapter-item expanded "><a href="Chapter_3.html"><strong aria-hidden="true">4.</strong> Writing Rust in Easy English</a></li><li class="chapter-item expanded "><a href="Chapter_4.html"><strong aria-hidden="true">5.</strong> Rust Playground</a></li><li class="chapter-item expanded "><a href="Chapter_5.html"><strong aria-hidden="true">6.</strong> 🚧 and ⚠️</a></li><li class="chapter-item expanded "><a href="Chapter_6.html"><strong aria-hidden="true">7.</strong> Comments</a></li><li class="chapter-item expanded "><a href="Chapter_7.html"><strong aria-hidden="true">8.</strong> Types</a></li><li class="chapter-item expanded "><a href="Chapter_8.html"><strong aria-hidden="true">9.</strong> Type inference</a></li><li class="chapter-item expanded "><a href="Chapter_9.html"><strong aria-hidden="true">10.</strong> Printing 'hello, world!'</a></li><li class="chapter-item expanded "><a href="Chapter_10.html"><strong aria-hidden="true">11.</strong> Display and debug</a></li><li class="chapter-item expanded "><a href="Chapter_11.html"><strong aria-hidden="true">12.</strong> Mutability (changing)</a></li><li class="chapter-item expanded "><a href="Chapter_12.html"><strong aria-hidden="true">13.</strong> The stack, the heap, and pointers</a></li><li class="chapter-item expanded "><a href="Chapter_13.html"><strong aria-hidden="true">14.</strong> More about printing</a></li><li class="chapter-item expanded "><a href="Chapter_14.html"><strong aria-hidden="true">15.</strong> Strings</a></li><li class="chapter-item expanded "><a href="Chapter_15.html"><strong aria-hidden="true">16.</strong> const and static</a></li><li class="chapter-item expanded "><a href="Chapter_16.html"><strong aria-hidden="true">17.</strong> More on references</a></li><li class="chapter-item expanded "><a href="Chapter_17.html"><strong aria-hidden="true">18.</strong> Mutable references</a></li><li class="chapter-item expanded "><a href="Chapter_18.html"><strong aria-hidden="true">19.</strong> Giving references to functions</a></li><li class="chapter-item expanded "><a href="Chapter_19.html"><strong aria-hidden="true">20.</strong> Copy types</a></li><li class="chapter-item expanded "><a href="Chapter_20.html"><strong aria-hidden="true">21.</strong> Collection types</a></li><li class="chapter-item expanded "><a href="Chapter_21.html"><strong aria-hidden="true">22.</strong> Vectors</a></li><li class="chapter-item expanded "><a href="Chapter_22.html"><strong aria-hidden="true">23.</strong> Tuples</a></li><li class="chapter-item expanded "><a href="Chapter_23.html"><strong aria-hidden="true">24.</strong> Control flow</a></li><li class="chapter-item expanded "><a href="Chapter_24.html"><strong aria-hidden="true">25.</strong> Structs</a></li><li class="chapter-item expanded "><a href="Chapter_25.html"><strong aria-hidden="true">26.</strong> Enums</a></li><li class="chapter-item expanded "><a href="Chapter_26.html"><strong aria-hidden="true">27.</strong> Loops</a></li><li class="chapter-item expanded "><a href="Chapter_27.html"><strong aria-hidden="true">28.</strong> Implementing structs and enums</a></li><li class="chapter-item expanded "><a href="Chapter_28.html"><strong aria-hidden="true">29.</strong> Destructuring</a></li><li class="chapter-item expanded "><a href="Chapter_29.html"><strong aria-hidden="true">30.</strong> References and the dot operator</a></li><li class="chapter-item expanded "><a href="Chapter_30.html"><strong aria-hidden="true">31.</strong> Generics</a></li><li class="chapter-item expanded "><a href="Chapter_31.html"><strong aria-hidden="true">32.</strong> Option and Result</a></li><li class="chapter-item expanded "><a href="Chapter_32.html"><strong aria-hidden="true">33.</strong> Other collections</a></li><li class="chapter-item expanded "><a href="Chapter_33.html"><strong aria-hidden="true">34.</strong> The ? operator</a></li><li class="chapter-item expanded "><a href="Chapter_34.html"><strong aria-hidden="true">35.</strong> Traits</a></li><li class="chapter-item expanded "><a href="Chapter_35.html"><strong aria-hidden="true">36.</strong> Chaining methods</a></li><li class="chapter-item expanded "><a href="Chapter_36.html"><strong aria-hidden="true">37.</strong> Iterators</a></li><li class="chapter-item expanded "><a href="Chapter_37.html"><strong aria-hidden="true">38.</strong> Closures</a></li><li class="chapter-item expanded "><a href="Chapter_38.html"><strong aria-hidden="true">39.</strong> The dbg! macro and .inspect</a></li><li class="chapter-item expanded "><a href="Chapter_39.html"><strong aria-hidden="true">40.</strong> Types of &str</a></li><li class="chapter-item expanded "><a href="Chapter_40.html"><strong aria-hidden="true">41.</strong> Lifetimes</a></li><li class="chapter-item expanded "><a href="Chapter_41.html"><strong aria-hidden="true">42.</strong> Interior mutability</a></li><li class="chapter-item expanded "><a href="Chapter_42.html"><strong aria-hidden="true">43.</strong> Cow</a></li><li class="chapter-item expanded "><a href="Chapter_43.html"><strong aria-hidden="true">44.</strong> Type aliases</a></li><li class="chapter-item expanded "><a href="Chapter_44.html"><strong aria-hidden="true">45.</strong> The todo! macro</a></li><li class="chapter-item expanded "><a href="Chapter_45.html"><strong aria-hidden="true">46.</strong> Rc</a></li><li class="chapter-item expanded "><a href="Chapter_46.html"><strong aria-hidden="true">47.</strong> Multiple threads</a></li><li class="chapter-item expanded "><a href="Chapter_47.html"><strong aria-hidden="true">48.</strong> Closures in functions</a></li><li class="chapter-item expanded "><a href="Chapter_48.html"><strong aria-hidden="true">49.</strong> impl Trait</a></li><li class="chapter-item expanded "><a href="Chapter_49.html"><strong aria-hidden="true">50.</strong> Arc</a></li><li class="chapter-item expanded "><a href="Chapter_50.html"><strong aria-hidden="true">51.</strong> Channels</a></li><li class="chapter-item expanded "><a href="Chapter_51.html"><strong aria-hidden="true">52.</strong> Reading Rust documentation</a></li><li class="chapter-item expanded "><a href="Chapter_52.html"><strong aria-hidden="true">53.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="Chapter_53.html"><strong aria-hidden="true">54.</strong> Box</a></li><li class="chapter-item expanded "><a href="Chapter_54.html"><strong aria-hidden="true">55.</strong> Box around traits</a></li><li class="chapter-item expanded "><a href="Chapter_55.html"><strong aria-hidden="true">56.</strong> Default and the builder pattern</a></li><li class="chapter-item expanded "><a href="Chapter_56.html"><strong aria-hidden="true">57.</strong> Deref and DerefMut</a></li><li class="chapter-item expanded "><a href="Chapter_57.html"><strong aria-hidden="true">58.</strong> Crates and modules</a></li><li class="chapter-item expanded "><a href="Chapter_58.html"><strong aria-hidden="true">59.</strong> Testing</a></li><li class="chapter-item expanded "><a href="Chapter_59.html"><strong aria-hidden="true">60.</strong> External crates</a></li><li class="chapter-item expanded "><a href="Chapter_60.html"><strong aria-hidden="true">61.</strong> A tour of the standard library</a></li><li class="chapter-item expanded "><a href="Chapter_61.html"><strong aria-hidden="true">62.</strong> Writing macros</a></li><li class="chapter-item expanded "><a href="Chapter_62.html"><strong aria-hidden="true">63.</strong> cargo</a></li><li class="chapter-item expanded "><a href="Chapter_63.html" class="active"><strong aria-hidden="true">64.</strong> Taking user input</a></li><li class="chapter-item expanded "><a href="Chapter_64.html"><strong aria-hidden="true">65.</strong> Using files</a></li><li class="chapter-item expanded "><a href="Chapter_65.html"><strong aria-hidden="true">66.</strong> cargo doc</a></li><li class="chapter-item expanded "><a href="Chapter_66.html"><strong aria-hidden="true">67.</strong> The end?</a></li></ol>
|
|
</div>
|
|
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
|
|
</nav>
|
|
|
|
<div id="page-wrapper" class="page-wrapper">
|
|
|
|
<div class="page">
|
|
|
|
<div id="menu-bar-hover-placeholder"></div>
|
|
<div id="menu-bar" class="menu-bar sticky bordered">
|
|
<div class="left-buttons">
|
|
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|
<i class="fa fa-bars"></i>
|
|
</button>
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|
<i class="fa fa-paint-brush"></i>
|
|
</button>
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|
</ul>
|
|
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|
<i class="fa fa-search"></i>
|
|
</button>
|
|
|
|
</div>
|
|
|
|
<h1 class="menu-title">Easy Rust</h1>
|
|
|
|
<div class="right-buttons">
|
|
|
|
<a href="print.html" title="Print this book" aria-label="Print this book">
|
|
<i id="print-button" class="fa fa-print"></i>
|
|
</a>
|
|
|
|
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<div id="search-wrapper" class="hidden">
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|
<input type="search" name="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|
</form>
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|
<ul id="searchresults">
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|
<script type="text/javascript">
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|
});
|
|
</script>
|
|
|
|
<div id="content" class="content">
|
|
<main>
|
|
<h2 id="taking-user-input"><a class="header" href="#taking-user-input">Taking user input</a></h2>
|
|
<p>One easy way to take input from the user is with <code>std::io::stdin</code>. This means "standard in", which is the input from the keyboard. With <code>stdin()</code> you can get user input, but then you will want to put it in a <code>&mut String</code> with <code>.read_line()</code>. Here is a simple example of that, but it both works and doesn't work:</p>
|
|
<pre><pre class="playground"><code class="language-rust">use std::io;
|
|
|
|
fn main() {
|
|
println!("Please type something, or x to escape:");
|
|
let mut input_string = String::new();
|
|
|
|
while input_string != "x" { // This is the part that doesn't work right
|
|
input_string.clear(); // First clear the String. Otherwise it will keep adding to it
|
|
io::stdin().read_line(&mut input_string).unwrap(); // Get the stdin from the user, and put it in read_string
|
|
println!("You wrote {}", input_string);
|
|
}
|
|
println!("See you later!");
|
|
}
|
|
</code></pre></pre>
|
|
<p>Here is what an output output looks like:</p>
|
|
<pre><code class="language-text">Please type something, or x to escape:
|
|
something
|
|
You wrote something
|
|
|
|
Something else
|
|
You wrote Something else
|
|
|
|
x
|
|
You wrote x
|
|
|
|
x
|
|
You wrote x
|
|
|
|
x
|
|
You wrote x
|
|
</code></pre>
|
|
<p>It takes our input and gives it back, and it even knows that we typed <code>x</code>. But it doesn't exit the program. The only way to get out is to close the window, or type ctrl and c. Let's change the <code>{}</code> to <code>{:?}</code> in <code>println!</code> to get more information (or you could use <code>dbg!(&input_string)</code> if you like that macro). Now it says:</p>
|
|
<pre><code class="language-text">Please type something, or x to escape:
|
|
something
|
|
You wrote "something\r\n"
|
|
Something else
|
|
You wrote "Something else\r\n"
|
|
x
|
|
You wrote "x\r\n"
|
|
x
|
|
You wrote "x\r\n"
|
|
</code></pre>
|
|
<p>This is because the keyboard input is actually not just <code>something</code>, it is <code>something</code> and the <code>Enter</code> key. There is an easy method to fix this called <code>.trim()</code>, which removes all the whitespace. Whitespace, by the way, is all <a href="https://doc.rust-lang.org/reference/whitespace.html">these characters</a>:</p>
|
|
<pre><code class="language-text">U+0009 (horizontal tab, '\t')
|
|
U+000A (line feed, '\n')
|
|
U+000B (vertical tab)
|
|
U+000C (form feed)
|
|
U+000D (carriage return, '\r')
|
|
U+0020 (space, ' ')
|
|
U+0085 (next line)
|
|
U+200E (left-to-right mark)
|
|
U+200F (right-to-left mark)
|
|
U+2028 (line separator)
|
|
U+2029 (paragraph separator)
|
|
</code></pre>
|
|
<p>So that will turn <code>x\r\n</code> into just <code>x</code>. Now it works:</p>
|
|
<pre><pre class="playground"><code class="language-rust">use std::io;
|
|
|
|
fn main() {
|
|
println!("Please type something, or x to escape:");
|
|
let mut input_string = String::new();
|
|
|
|
while input_string.trim() != "x" {
|
|
input_string.clear();
|
|
io::stdin().read_line(&mut input_string).unwrap();
|
|
println!("You wrote {}", input_string);
|
|
}
|
|
println!("See you later!");
|
|
}
|
|
</code></pre></pre>
|
|
<p>Now it will print:</p>
|
|
<pre><code class="language-text">Please type something, or x to escape:
|
|
something
|
|
You wrote something
|
|
|
|
Something
|
|
You wrote Something
|
|
|
|
x
|
|
You wrote x
|
|
|
|
See you later!
|
|
</code></pre>
|
|
<p>There is another kind of user input called <code>std::env::Args</code> (env means environment). <code>Args</code> is what the user types when starting the program. There is actually always at least one <code>Arg</code> in a program. Let's write a program that only prints them using <code>std::env::args()</code> to see what they are.</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
println!("{:?}", std::env::args());
|
|
}
|
|
</code></pre></pre>
|
|
<p>If we write <code>cargo run</code> then it prints something like this:</p>
|
|
<pre><code class="language-text">Args { inner: ["target\\debug\\rust_book.exe"] }
|
|
</code></pre>
|
|
<p>Let's give it more input and see what it does. We'll type <code>cargo run but with some extra words</code>. It gives us:</p>
|
|
<pre><code class="language-text">Args { inner: ["target\\debug\\rust_book.exe", "but", "with", "some", "extra", "words"] }
|
|
</code></pre>
|
|
<p>Interesting. And when we look at <a href="https://doc.rust-lang.org/std/env/struct.Args.html">the page for Args</a>, we see that it implements <code>IntoIterator</code>. That means we can do all the things we know about iterators to read and change it. Let's try this:</p>
|
|
<pre><pre class="playground"><code class="language-rust">use std::env::args;
|
|
|
|
fn main() {
|
|
let input = args();
|
|
|
|
for entry in input {
|
|
println!("You entered: {}", entry);
|
|
}
|
|
}
|
|
</code></pre></pre>
|
|
<p>Now it says:</p>
|
|
<pre><code class="language-text">You entered: target\debug\rust_book.exe
|
|
You entered: but
|
|
You entered: with
|
|
You entered: some
|
|
You entered: extra
|
|
You entered: words
|
|
</code></pre>
|
|
<p>You can see that the first argument is always the program name, so you will often want to skip it, like this:</p>
|
|
<pre><pre class="playground"><code class="language-rust">use std::env::args;
|
|
|
|
fn main() {
|
|
let input = args();
|
|
|
|
input.into_iter().skip(1).for_each(|item| {
|
|
println!("You wrote {}, which in capital letters is {}", item, item.to_uppercase());
|
|
})
|
|
}
|
|
</code></pre></pre>
|
|
<p>That will print:</p>
|
|
<pre><code class="language-text">You wrote but, which in capital letters is BUT
|
|
You wrote with, which in capital letters is WITH
|
|
You wrote some, which in capital letters is SOME
|
|
You wrote extra, which in capital letters is EXTRA
|
|
You wrote words, which in capital letters is WORDS
|
|
</code></pre>
|
|
<p>One common use for <code>Args</code> is for user settings. You can make sure that the user writes the input you need, and only run the program if it's right. Here's a small program that either makes letters big (capital) or small (lowercase):</p>
|
|
<pre><pre class="playground"><code class="language-rust">use std::env::args;
|
|
|
|
fn main() {
|
|
let keywords = ["capital".to_string(), "lowercase".to_string()]; // User needs to write one of these after cargo run
|
|
let input_vec = args().into_iter().collect::<Vec<String>>(); // Make a vec of all the args
|
|
|
|
if input_vec.len() > 2 && keywords.contains(&input_vec[1].to_lowercase()) { // It must be at least 3 in length, and the user needs to write either "capital" or "lowercase".
|
|
// We use .to_lowercase() so the user can write "Capital" or "CAPITAL", etc.
|
|
if input_vec[1].to_lowercase() == "capital" {
|
|
input_vec.into_iter().skip(2).for_each(|word| println!("{}", word.to_uppercase()));
|
|
} else {
|
|
input_vec.into_iter().skip(2).for_each(|word| println!("{}", word.to_lowercase()));
|
|
}
|
|
} else {
|
|
println!(r#"Please write either "capital" or "lowercase" and then some input."#);
|
|
}
|
|
}
|
|
</code></pre></pre>
|
|
<p>Here are some examples of what it gives:</p>
|
|
<p>Input: <code>cargo run please make capitals</code>:</p>
|
|
<pre><code class="language-text">Please write either "capital" or "lowercase" and then some input.
|
|
</code></pre>
|
|
<p>Input: <code>cargo run capital</code>:</p>
|
|
<pre><code class="language-text">Please write either "capital" or "lowercase" and then some input.
|
|
</code></pre>
|
|
<p>Input: <code>cargo run capital I think I understand now</code>:</p>
|
|
<pre><code class="language-text">I
|
|
THINK
|
|
I
|
|
UNDERSTAND
|
|
NOW
|
|
</code></pre>
|
|
<p>Input: <code>cargo run LOWERCASE Does this work too?</code></p>
|
|
<pre><code class="language-text">does
|
|
this
|
|
work
|
|
too?
|
|
</code></pre>
|
|
<p>Besides <code>Args</code> given by the user in <code>std::env</code>, there are also <code>Vars</code> which are the system variables. Those are the basic settings for the program that the user didn't type in. You can use <code>std::env::vars()</code> to see them all as a <code>(String, String)</code>. There are very many. For example:</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
for item in std::env::vars() {
|
|
println!("{:?}", item);
|
|
}
|
|
}
|
|
</code></pre></pre>
|
|
<p>Just doing this shows you all the information about your user session. It will show information like this:</p>
|
|
<pre><code class="language-text">("CARGO", "/playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo")
|
|
("CARGO_HOME", "/playground/.cargo")
|
|
("CARGO_MANIFEST_DIR", "/playground")
|
|
("CARGO_PKG_AUTHORS", "The Rust Playground")
|
|
("CARGO_PKG_DESCRIPTION", "")
|
|
("CARGO_PKG_HOMEPAGE", "")
|
|
("CARGO_PKG_NAME", "playground")
|
|
("CARGO_PKG_REPOSITORY", "")
|
|
("CARGO_PKG_VERSION", "0.0.1")
|
|
("CARGO_PKG_VERSION_MAJOR", "0")
|
|
("CARGO_PKG_VERSION_MINOR", "0")
|
|
("CARGO_PKG_VERSION_PATCH", "1")
|
|
("CARGO_PKG_VERSION_PRE", "")
|
|
("DEBIAN_FRONTEND", "noninteractive")
|
|
("HOME", "/playground")
|
|
("HOSTNAME", "f94c15b8134b")
|
|
("LD_LIBRARY_PATH", "/playground/target/debug/build/backtrace-sys-3ec4c973f371c302/out:/playground/target/debug/build/libsqlite3-sys-fbddfbb9b241dacb/out:/playground/target/debug/build/ring-cadba5e583648abb/out:/playground/target/debug/deps:/playground/target/debug:/playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib:/playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib")
|
|
("PATH", "/playground/.cargo/bin:/playground/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin")
|
|
("PLAYGROUND_EDITION", "2018")
|
|
("PLAYGROUND_TIMEOUT", "10")
|
|
("PWD", "/playground")
|
|
("RUSTUP_HOME", "/playground/.rustup")
|
|
("RUSTUP_TOOLCHAIN", "stable-x86_64-unknown-linux-gnu")
|
|
("RUST_RECURSION_COUNT", "1")
|
|
("SHLVL", "1")
|
|
("SSL_CERT_DIR", "/usr/lib/ssl/certs")
|
|
("SSL_CERT_FILE", "/usr/lib/ssl/certs/ca-certificates.crt")
|
|
("USER", "playground")
|
|
("_", "/usr/bin/timeout")
|
|
</code></pre>
|
|
<p>So if you need this information, <code>Vars</code> is what you want.</p>
|
|
<p>The easiest way to get a single <code>Var</code> is by using the <code>env!</code> macro. You just put the name of the variable inside it, and it will give you a <code>&str</code>. It won't work if the variable is wrong though, so if you aren't sure then use <code>option_env!</code> instead. If we write this on the Playground:</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
println!("{}", env!("USER"));
|
|
println!("{}", option_env!("ROOT").unwrap_or("Didn't work"));
|
|
println!("{}", option_env!("CARGO").unwrap_or("Didn't work"));
|
|
}
|
|
</code></pre></pre>
|
|
<p>then we get the output:</p>
|
|
<pre><code class="language-text">playground
|
|
Didn't work
|
|
/playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo
|
|
</code></pre>
|
|
<p>So <code>option_env!</code> is always going to be the safer macro. <code>env!</code> is better if you actually want the program to crash when you can't find the environment variable.</p>
|
|
|
|
</main>
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
<!-- Mobile navigation buttons -->
|
|
|
|
<a rel="prev" href="Chapter_62.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a rel="next" href="Chapter_64.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
|
|
<div style="clear: both"></div>
|
|
</nav>
|
|
</div>
|
|
</div>
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
|
|
<a rel="prev" href="Chapter_62.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a rel="next" href="Chapter_64.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
</nav>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script type="text/javascript">
|
|
window.playground_copyable = true;
|
|
</script>
|
|
|
|
|
|
|
|
|
|
|
|
<script src="elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="mark.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="searcher.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
|
|
<script src="clipboard.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="highlight.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="book.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
<!-- Custom JS scripts -->
|
|
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|