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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: Directories</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'file-paths';
}
if (e.key == "ArrowRight") {
window.location.href = 'temporary-files-and-directories';
}
}
</script>
<body>
<div class="example" id="directories">
<h2><a href="./">Go by Example</a>: Directories</h2>
<table>
<tr>
<td class="docs">
<p>Go has several useful functions for working with
<em>directories</em> in the file system.</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/UaeLMS5VQVR"><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>Create a new sub-directory in the current working
directory.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Mkdir</span><span class="p">(</span><span class="s">&quot;subdir&quot;</span><span class="p">,</span> <span class="mo">0755</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>When creating temporary directories, it&rsquo;s good
practice to <code>defer</code> their removal. <code>os.RemoveAll</code>
will delete a whole directory tree (similarly to
<code>rm -rf</code>).</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">RemoveAll</span><span class="p">(</span><span class="s">&quot;subdir&quot;</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Helper function to create a new empty file.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">createEmptyFile</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">name</span> <span class="kt">string</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">d</span> <span class="o">:=</span> <span class="p">[]</span><span class="nb">byte</span><span class="p">(</span><span class="s">&quot;&quot;</span><span class="p">)</span>
<span class="nx">check</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">name</span><span class="p">,</span> <span class="nx">d</span><span class="p">,</span> <span class="mo">0644</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="nx">createEmptyFile</span><span class="p">(</span><span class="s">&quot;subdir/file1&quot;</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>We can create a hierarchy of directories, including
parents with <code>MkdirAll</code>. This is similar to the
command-line <code>mkdir -p</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">err</span> <span class="p">=</span> <span class="nx">os</span><span class="p">.</span><span class="nx">MkdirAll</span><span class="p">(</span><span class="s">&quot;subdir/parent/child&quot;</span><span class="p">,</span> <span class="mo">0755</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">
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">createEmptyFile</span><span class="p">(</span><span class="s">&quot;subdir/parent/file2&quot;</span><span class="p">)</span>
<span class="nx">createEmptyFile</span><span class="p">(</span><span class="s">&quot;subdir/parent/file3&quot;</span><span class="p">)</span>
<span class="nx">createEmptyFile</span><span class="p">(</span><span class="s">&quot;subdir/parent/child/file4&quot;</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>ReadDir</code> lists directory contents, returning a
slice of <code>os.FileInfo</code> objects.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">c</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">ReadDir</span><span class="p">(</span><span class="s">&quot;subdir/parent&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">
</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;Listing subdir/parent&quot;</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">entry</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">c</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; &quot;</span><span class="p">,</span> <span class="nx">entry</span><span class="p">.</span><span class="nx">Name</span><span class="p">(),</span> <span class="nx">entry</span><span class="p">.</span><span class="nx">IsDir</span><span class="p">())</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>Chdir</code> lets us change the current working directory,
similarly to <code>cd</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">err</span> <span class="p">=</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Chdir</span><span class="p">(</span><span class="s">&quot;subdir/parent/child&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>Now we&rsquo;ll see the contents of <code>subdir/parent/child</code>
when listing the <em>current</em> directory.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">c</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">ReadDir</span><span class="p">(</span><span class="s">&quot;.&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">
</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;Listing subdir/parent/child&quot;</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">entry</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">c</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; &quot;</span><span class="p">,</span> <span class="nx">entry</span><span class="p">.</span><span class="nx">Name</span><span class="p">(),</span> <span class="nx">entry</span><span class="p">.</span><span class="nx">IsDir</span><span class="p">())</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>cd</code> back to where we started.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">err</span> <span class="p">=</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Chdir</span><span class="p">(</span><span class="s">&quot;../../..&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>We can also visit a directory <em>recursively</em>,
including all its sub-directories. <code>Walk</code> accepts
a callback function to handle every file or
directory visited.</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;Visiting subdir&quot;</span><span class="p">)</span>
<span class="nx">err</span> <span class="p">=</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Walk</span><span class="p">(</span><span class="s">&quot;subdir&quot;</span><span class="p">,</span> <span class="nx">visit</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>visit</code> is called for every file or directory found
recursively by <code>filepath.Walk</code>.</p>
</td>
<td class="code">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">visit</span><span class="p">(</span><span class="nx">p</span> <span class="kt">string</span><span class="p">,</span> <span class="nx">info</span> <span class="nx">os</span><span class="p">.</span><span class="nx">FileInfo</span><span class="p">,</span> <span class="nx">err</span> <span class="kt">error</span><span class="p">)</span> <span class="kt">error</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">err</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="k">return</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; &quot;</span><span class="p">,</span> <span class="nx">p</span><span class="p">,</span> <span class="nx">info</span><span class="p">.</span><span class="nx">IsDir</span><span class="p">())</span>
<span class="k">return</span> <span class="kc">nil</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 directories.go
<span class="go">Listing subdir/parent</span>
<span class="go"> child true</span>
<span class="go"> file2 false</span>
<span class="go"> file3 false</span>
<span class="go">Listing subdir/parent/child</span>
<span class="go"> file4 false</span>
<span class="go">Visiting subdir</span>
<span class="go"> subdir true</span>
<span class="go"> subdir/file1 false</span>
<span class="go"> subdir/parent true</span>
<span class="go"> subdir/parent/child true</span>
<span class="go"> subdir/parent/child/file4 false</span>
<span class="go"> subdir/parent/file2 false</span>
<span class="go"> subdir/parent/file3 false</span>
</pre></div>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="temporary-files-and-directories">Temporary Files and Directories</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/directories">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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