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gobyexample/public/file-paths
Mark McGranaghan a1fd3bf037 Regenerate
2020-04-10 17:49:18 -07:00

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<title>Go by Example: File Paths</title>
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<div class="example" id="file-paths">
<h2><a href="./">Go by Example</a>: File Paths</h2>
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<p>The <code>filepath</code> package provides functions to parse
and construct <em>file paths</em> in a way that is portable
between operating systems; <code>dir/file</code> on Linux vs.
<code>dir\file</code> on Windows, for example.</p>
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<td class="code leading">
<a href="http://play.golang.org/p/5h3lUytvmyO"><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>
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<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
<span class="s">&quot;fmt&quot;</span>
<span class="s">&quot;path/filepath&quot;</span>
<span class="s">&quot;strings&quot;</span>
<span class="p">)</span>
</pre></div>
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
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<p><code>Join</code> should be used to construct paths in a
portable way. It takes any number of arguments
and constructs a hierarchical path from them.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">p</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="s">&quot;dir1&quot;</span><span class="p">,</span> <span class="s">&quot;dir2&quot;</span><span class="p">,</span> <span class="s">&quot;filename&quot;</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;p:&quot;</span><span class="p">,</span> <span class="nx">p</span><span class="p">)</span>
</pre></div>
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<p>You should always use <code>Join</code> instead of
concatenating <code>/</code>s or <code>\</code>s manually. In addition
to providing portability, <code>Join</code> will also
normalize paths by removing superfluous separators
and directory changes.</p>
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<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="nx">filepath</span><span class="p">.</span><span class="nx">Join</span><span class="p">(</span><span class="s">&quot;dir1//&quot;</span><span class="p">,</span> <span class="s">&quot;filename&quot;</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="nx">filepath</span><span class="p">.</span><span class="nx">Join</span><span class="p">(</span><span class="s">&quot;dir1/../dir1&quot;</span><span class="p">,</span> <span class="s">&quot;filename&quot;</span><span class="p">))</span>
</pre></div>
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<p><code>Dir</code> and <code>Base</code> can be used to split a path to the
directory and the file. Alternatively, <code>Split</code> will
return both in the same call.</p>
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<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;Dir(p):&quot;</span><span class="p">,</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Dir</span><span class="p">(</span><span class="nx">p</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;Base(p):&quot;</span><span class="p">,</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Base</span><span class="p">(</span><span class="nx">p</span><span class="p">))</span>
</pre></div>
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<p>We can check whether a path is absolute.</p>
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<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="nx">filepath</span><span class="p">.</span><span class="nx">IsAbs</span><span class="p">(</span><span class="s">&quot;dir/file&quot;</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="nx">filepath</span><span class="p">.</span><span class="nx">IsAbs</span><span class="p">(</span><span class="s">&quot;/dir/file&quot;</span><span class="p">))</span>
</pre></div>
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<div class="highlight"><pre> <span class="nx">filename</span> <span class="o">:=</span> <span class="s">&quot;config.json&quot;</span>
</pre></div>
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<p>Some file names have extensions following a dot. We
can split the extension out of such names with <code>Ext</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">ext</span> <span class="o">:=</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Ext</span><span class="p">(</span><span class="nx">filename</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="nx">ext</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>To find the file&rsquo;s name with the extension removed,
use <code>strings.TrimSuffix</code>.</p>
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<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="nx">strings</span><span class="p">.</span><span class="nx">TrimSuffix</span><span class="p">(</span><span class="nx">filename</span><span class="p">,</span> <span class="nx">ext</span><span class="p">))</span>
</pre></div>
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<p><code>Rel</code> finds a relative path between a <em>base</em> and a
<em>target</em>. It returns an error if the target cannot
be made relative to base.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">rel</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">filepath</span><span class="p">.</span><span class="nx">Rel</span><span class="p">(</span><span class="s">&quot;a/b&quot;</span><span class="p">,</span> <span class="s">&quot;a/b/t/file&quot;</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="nb">panic</span><span class="p">(</span><span class="nx">err</span><span class="p">)</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="nx">rel</span><span class="p">)</span>
</pre></div>
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</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">rel</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">Rel</span><span class="p">(</span><span class="s">&quot;a/b&quot;</span><span class="p">,</span> <span class="s">&quot;a/c/t/file&quot;</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="nb">panic</span><span class="p">(</span><span class="nx">err</span><span class="p">)</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="nx">rel</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
</td>
<td class="code">
<div class="highlight"><pre><span class="gp">$</span> go run file-paths.go
<span class="go">p: dir1/dir2/filename</span>
<span class="go">dir1/filename</span>
<span class="go">dir1/filename</span>
<span class="go">Dir(p): dir1/dir2</span>
<span class="go">Base(p): filename</span>
<span class="go">false</span>
<span class="go">true</span>
<span class="go">.json</span>
<span class="go">config</span>
<span class="go">t/file</span>
<span class="go">../c/t/file</span>
</pre></div>
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<p class="next">
Next example: <a href="directories">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/file-paths">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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