250 lines
11 KiB
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Generated
250 lines
11 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Temporary Files and Directories</title>
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<link rel=stylesheet href="site.css">
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if (e.key == "ArrowLeft") {
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window.location.href = 'directories';
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<body>
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<div class="example" id="temporary-files-and-directories">
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<h2><a href="./">Go by Example</a>: Temporary Files and Directories</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Throughout program execution, we often want to create
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data that isn’t needed after the program exits.
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<em>Temporary files and directories</em> are useful for this
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purpose since they don’t pollute the file system over
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time.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<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" />
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"io/ioutil"</span>
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<span class="s">"os"</span>
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<span class="s">"path/filepath"</span>
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<span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<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>
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<span class="k">if</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nb">panic</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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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>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The easiest way to create a temporary file is by
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calling <code>ioutil.TempFile</code>. It creates a file <em>and</em>
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opens it for reading and writing. We provide <code>""</code>
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as the first argument, so <code>ioutil.TempFile</code> will
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create the file in the default location for our OS.</p>
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</td>
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<td class="code leading">
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<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">""</span><span class="p">,</span> <span class="s">"sample"</span><span class="p">)</span>
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<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Display the name of the temporary file. On
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Unix-based OSes the directory will likely be <code>/tmp</code>.
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The file name starts with the prefix given as the
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second argument to <code>ioutil.TempFile</code> and the rest
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is chosen automatically to ensure that concurrent
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calls will always create different file names.</p>
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</td>
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<td class="code leading">
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<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">"Temp file name:"</span><span class="p">,</span> <span class="nx">f</span><span class="p">.</span><span class="nx">Name</span><span class="p">())</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Clean up the file after we’re done. The OS is
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likely to clean up temporary files by itself after
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some time, but it’s good practice to do this
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explicitly.</p>
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</td>
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<td class="code leading">
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<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>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>We can write some data to the file.</p>
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</td>
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<td class="code leading">
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<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>
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<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>If we intend to write many temporary files, we may
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prefer to create a temporary <em>directory</em>.
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<code>ioutil.TempDir</code>’s arguments are the same as
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<code>TempFile</code>’s, but it returns a directory <em>name</em>
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rather than an open file.</p>
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</td>
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<td class="code leading">
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<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">""</span><span class="p">,</span> <span class="s">"sampledir"</span><span class="p">)</span>
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<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"Temp dir name:"</span><span class="p">,</span> <span class="nx">dname</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<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>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Now we can synthesize temporary file names by
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prefixing them with our temporary directory.</p>
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</td>
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<td class="code">
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<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">"file1"</span><span class="p">)</span>
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<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>
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<span class="nx">check</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run temporary-files-and-directories.go
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<span class="go">Temp file name: /tmp/sample610887201</span>
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<span class="go">Temp dir name: /tmp/sampledir898854668</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="testing">Testing</a>.
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</p>
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<p class="footer">
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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>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"io/ioutil\"\u000A \"os\"\u000A \"path/filepath\"\u000A)\u000A');codeLines.push('func check(e error) {\u000A if e != nil {\u000A panic(e)\u000A }\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' f, err := ioutil.TempFile(\"\", \"sample\")\u000A check(err)\u000A');codeLines.push(' fmt.Println(\"Temp file name:\", f.Name())\u000A');codeLines.push(' defer os.Remove(f.Name())\u000A');codeLines.push(' _, err = f.Write([]byte{1, 2, 3, 4})\u000A check(err)\u000A');codeLines.push(' dname, err := ioutil.TempDir(\"\", \"sampledir\")\u000A check(err)\u000A fmt.Println(\"Temp dir name:\", dname)\u000A');codeLines.push(' defer os.RemoveAll(dname)\u000A');codeLines.push(' fname := filepath.Join(dname, \"file1\")\u000A err = ioutil.WriteFile(fname, []byte{1, 2}, 0666)\u000A check(err)\u000A}\u000A');codeLines.push('');
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