Temporary files and directories sample

Followup on discussion in #243
2019-06-17 06:01:41 -07:00 · 2019-06-17 06:01:41 -07:00 · 8219122e44
commit 8219122e44
parent f9050decb5
7 changed files with 307 additions and 1 deletions
--- a/examples.txt
+++ b/examples.txt
@ -56,6 +56,7 @@ SHA1 Hashes
 Base64 Encoding
 Reading Files
 Writing Files
+Temporary Files and Directories
 Line Filters
 File Paths
 Directories
--- a/examples/temporary-files-and-directories/temporary-files-and-directories.go
+++ b/examples/temporary-files-and-directories/temporary-files-and-directories.go
@ -0,0 +1,65 @@
+// Throughout program execution, we often want to create
+// data that isn't needed after the program exits.
+// *Temporary files and directories* are useful for this
+// purpose since they don't pollute the file system over
+// time.
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+func main() {
+
+	// The easiest way to create a temporary file is by
+	// calling `ioutil.TempFile`. It creates a file *and*
+	// opens it for reading and writing. We provide `""`
+	// as the first argument, so `ioutil.TempFile` will
+	// create the file in the default location for our OS.
+	f, err := ioutil.TempFile("", "sample")
+	check(err)
+
+	// Display the name of the temporary file. On
+	// Unix-based OSes the directory will likely be `/tmp`.
+	// The file name starts with the prefix given as the
+	// second argument to `ioutil.TempFile` and the rest
+	// is chosen automatically to ensure that concurrent
+	// calls will always create different file names.
+	fmt.Println("Temp file name:", f.Name())
+
+	// Clean up the file after we're done. The OS is
+	// likely to clean up temporary files by itself after
+	// some time, but it's good practice to do this
+	// explicitly.
+	defer os.Remove(f.Name())
+
+	// We can write some data to the file.
+	_, err = f.Write([]byte{1, 2, 3, 4})
+	check(err)
+
+	// If we intend to write many temporary files, we may
+	// prefer to create a temporary *directory*.
+	// `ioutil.TempDir`'s arguments are the same as
+	// `TempFile`'s, but it returns a directory *name*
+	// rather than an open file.
+	dname, err := ioutil.TempDir("", "sampledir")
+	fmt.Println("Temp dir name:", dname)
+
+	defer os.RemoveAll(dname)
+
+	// Now we can synthesize temporary file names by
+	// prefixing them with our temporary directory.
+	fname := filepath.Join(dname, "file1")
+	err = ioutil.WriteFile(fname, []byte{1, 2}, 0666)
+	check(err)
+}
--- a/examples/temporary-files-and-directories/temporary-files-and-directories.hash
+++ b/examples/temporary-files-and-directories/temporary-files-and-directories.hash
@ -0,0 +1,2 @@
+5f7d0c43988d7dce235adb06ec02f4d2026b7f83
+pxE20wGTFjv
--- a/examples/temporary-files-and-directories/temporary-files-and-directories.sh
+++ b/examples/temporary-files-and-directories/temporary-files-and-directories.sh
@ -0,0 +1,4 @@
+# The exact names printed out will likely be different.
+$ go run temporary-files-and-directories.go
+Temp file name: /tmp/sample610887201
+Temp dir name: /tmp/sampledir898854668
--- a/public/index.html
+++ b/public/index.html
@ -139,6 +139,8 @@
      
        <li><a href="writing-files">Writing Files</a></li>
      
+        <li><a href="temporary-files-and-directories">Temporary Files and Directories</a></li>
+      
        <li><a href="line-filters">Line Filters</a></li>
      
        <li><a href="file-paths">File Paths</a></li>
--- a/public/temporary-files-and-directories
+++ b/public/temporary-files-and-directories
@ -0,0 +1,232 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>Go by Example: Temporary Files and Directories</title>
+    <link rel=stylesheet href="site.css">
+  </head>
+  <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/pxE20wGTFjv">
+              <img title="Run code" class="run" src="data:image/png;base64,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" />
+            </a>
+            <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">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">
+            <p>The exact names printed out will likely be different.</p>
+
+          </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="line-filters">Line Filters</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>
+  </body>
+</html>
--- a/public/writing-files
+++ b/public/writing-files
@ -266,7 +266,7 @@ we&rsquo;ve just seen to the <code>stdin</code> and <code>stdout</code> streams.
      
      
      <p class="next">
-        Next example: <a href="line-filters">Line Filters</a>.
+        Next example: <a href="temporary-files-and-directories">Temporary Files and Directories</a>.
      </p>
      
      <p class="footer">