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gobyexample/public/temporary-files-and-directories
Hana 9e216da9ef go.mod: add go.mod and move pygments to third_party 
After go1.16, go will use module mode by default,
even when the repository is checked out under GOPATH
or in a one-off directory. Add go.mod, go.sum to keep
this repo buildable without opting out of the module
mode.

> go mod init github.com/mmcgrana/gobyexample
> go mod tidy
> go mod vendor

In module mode, the 'vendor' directory is special
and its contents will be actively maintained by the
go command. pygments aren't the dependency the go will
know about, so it will delete the contents from vendor
directory. Move it to `third_party` directory now.

And, vendor the blackfriday package.

Note: the tutorial contents are not affected by the
change in go1.16 because all the examples in this
tutorial ask users to run the go command with the
explicit list of files to be compiled (e.g.
`go run hello-world.go` or `go build command-line-arguments.go`).
When the source list is provided, the go command does
not have to compute the build list and whether it's
running in GOPATH mode or module mode becomes irrelevant.
2021-02-15 16:45:26 -05:00

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Temporary Files and Directories</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'directories';
}
if (e.key == "ArrowRight") {
window.location.href = 'testing';
}
}
</script>
<body>
<div class="example" id="temporary-files-and-directories">
<h2><a href="./">Go by Example</a>: Temporary Files and Directories</h2>
<table>
<tr>
<td class="docs">
<p>Throughout program execution, we often want to create
data that isn&rsquo;t needed after the program exits.
<em>Temporary files and directories</em> are useful for this
purpose since they don&rsquo;t pollute the file system over
time.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/nMpjCsALS6P"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;io/ioutil&quot;</span>
<span class="s">&quot;os&quot;</span>
<span class="s">&quot;path/filepath&quot;</span>
<span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">check</span><span class="p">(</span><span class="nx">e</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="nb">panic</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>The easiest way to create a temporary file is by
calling <code>ioutil.TempFile</code>. It creates a file <em>and</em>
opens it for reading and writing. We provide <code>&quot;&quot;</code>
as the first argument, so <code>ioutil.TempFile</code> will
create the file in the default location for our OS.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">f</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">ioutil</span><span class="p">.</span><span class="nx">TempFile</span><span class="p">(</span><span class="s">&quot;&quot;</span><span class="p">,</span> <span class="s">&quot;sample&quot;</span><span class="p">)</span>
<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Display the name of the temporary file. On
Unix-based OSes the directory will likely be <code>/tmp</code>.
The file name starts with the prefix given as the
second argument to <code>ioutil.TempFile</code> and the rest
is chosen automatically to ensure that concurrent
calls will always create different file names.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Temp file name:&quot;</span><span class="p">,</span> <span class="nx">f</span><span class="p">.</span><span class="nx">Name</span><span class="p">())</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Clean up the file after we&rsquo;re done. The OS is
likely to clean up temporary files by itself after
some time, but it&rsquo;s good practice to do this
explicitly.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">defer</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Remove</span><span class="p">(</span><span class="nx">f</span><span class="p">.</span><span class="nx">Name</span><span class="p">())</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>We can write some data to the file.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">_</span><span class="p">,</span> <span class="nx">err</span> <span class="p">=</span> <span class="nx">f</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="kt">byte</span><span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">})</span>
<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>If we intend to write many temporary files, we may
prefer to create a temporary <em>directory</em>.
<code>ioutil.TempDir</code>&rsquo;s arguments are the same as
<code>TempFile</code>&rsquo;s, but it returns a directory <em>name</em>
rather than an open file.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">dname</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">ioutil</span><span class="p">.</span><span class="nx">TempDir</span><span class="p">(</span><span class="s">&quot;&quot;</span><span class="p">,</span> <span class="s">&quot;sampledir&quot;</span><span class="p">)</span>
<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;Temp dir name:&quot;</span><span class="p">,</span> <span class="nx">dname</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">defer</span> <span class="nx">os</span><span class="p">.</span><span class="nx">RemoveAll</span><span class="p">(</span><span class="nx">dname</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Now we can synthesize temporary file names by
prefixing them with our temporary directory.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">fname</span> <span class="o">:=</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Join</span><span class="p">(</span><span class="nx">dname</span><span class="p">,</span> <span class="s">&quot;file1&quot;</span><span class="p">)</span>
<span class="nx">err</span> <span class="p">=</span> <span class="nx">ioutil</span><span class="p">.</span><span class="nx">WriteFile</span><span class="p">(</span><span class="nx">fname</span><span class="p">,</span> <span class="p">[]</span><span class="kt">byte</span><span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">},</span> <span class="mo">0666</span><span class="p">)</span>
<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<div class="highlight"><pre><span class="gp">$</span> go run temporary-files-and-directories.go
<span class="go">Temp file name: /tmp/sample610887201</span>
<span class="go">Temp dir name: /tmp/sampledir898854668</span>
</pre></div>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="testing">Testing</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/temporary-files-and-directories">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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