198 lines
9.5 KiB
Plaintext
Generated
198 lines
9.5 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: Embed Directive</title>
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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'temporary-files-and-directories';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'testing-and-benchmarking';
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}
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}
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</script>
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<body>
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<div class="example" id="embed-directive">
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<h2><a href="./">Go by Example</a>: Embed Directive</h2>
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<table>
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<tr>
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<td class="docs">
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<p><code>//go:embed</code> is a <a href="https://pkg.go.dev/cmd/compile#hdr-Compiler_Directives">compiler
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directive</a> that
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allows programs to include arbitrary files and folders in the Go binary at
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build time. Read more about the embed directive
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<a href="https://pkg.go.dev/embed">here</a>.</p>
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</td>
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<td class="code leading">
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<a href="https://go.dev/play/p/6m2ll-D52BB"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
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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>Import the <code>embed</code> package; if you don’t use any exported
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identifiers from this package, you can do a blank import with <code>_ "embed"</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="p">(</span>
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</span></span><span class="line"><span class="cl"> <span class="s">"embed"</span>
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</span></span><span class="line"><span class="cl"><span class="p">)</span></span></span></code></pre>
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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><code>embed</code> directives accept paths relative to the directory containing the
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Go source file. This directive embeds the contents of the file into the
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<code>string</code> variable immediately following it.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="c1">//go:embed folder/single_file.txt
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</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="kd">var</span> <span class="nx">fileString</span> <span class="kt">string</span></span></span></code></pre>
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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>Or embed the contents of the file into a <code>[]byte</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="c1">//go:embed folder/single_file.txt
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</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="kd">var</span> <span class="nx">fileByte</span> <span class="p">[]</span><span class="kt">byte</span></span></span></code></pre>
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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 also embed multiple files or even folders with wildcards. This uses
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a variable of the <a href="https://pkg.go.dev/embed#FS">embed.FS type</a>, which
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implements a simple virtual file system.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="c1">//go:embed folder/single_file.txt
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</span></span></span><span class="line"><span class="cl"><span class="c1">//go:embed folder/*.hash
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</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="kd">var</span> <span class="nx">folder</span> <span class="nx">embed</span><span class="p">.</span><span class="nx">FS</span></span></span></code></pre>
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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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<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span></span></code></pre>
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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>Print out the contents of <code>single_file.txt</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nb">print</span><span class="p">(</span><span class="nx">fileString</span><span class="p">)</span>
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</span></span><span class="line"><span class="cl"> <span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">fileByte</span><span class="p">))</span></span></span></code></pre>
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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>Retrieve some files from the embedded folder.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">content1</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">folder</span><span class="p">.</span><span class="nf">ReadFile</span><span class="p">(</span><span class="s">"folder/file1.hash"</span><span class="p">)</span>
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</span></span><span class="line"><span class="cl"> <span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">content1</span><span class="p">))</span></span></span></code></pre>
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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">
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<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">content2</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">folder</span><span class="p">.</span><span class="nf">ReadFile</span><span class="p">(</span><span class="s">"folder/file2.hash"</span><span class="p">)</span>
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</span></span><span class="line"><span class="cl"> <span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">content2</span><span class="p">))</span>
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</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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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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<p>Use these commands to run the example.
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(Note: due to limitation on go playground,
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this example can only be run on your local machine.)</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> mkdir -p folder
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</span></span><span class="line"><span class="cl"><span class="gp">$</span> echo "hello go" > folder/single_file.txt
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</span></span><span class="line"><span class="cl"><span class="gp">$</span> echo "123" > folder/file1.hash
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</span></span><span class="line"><span class="cl"><span class="gp">$</span> echo "456" > folder/file2.hash</span></span></code></pre>
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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">
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<pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run embed-directive.go
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</span></span><span class="line"><span class="cl"><span class="go">hello go
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</span></span></span><span class="line"><span class="cl"><span class="go">hello go
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</span></span></span><span class="line"><span class="cl"><span class="go">123
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</span></span></span><span class="line"><span class="cl"><span class="go">456</span></span></span></code></pre>
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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-and-benchmarking">Testing and Benchmarking</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> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">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('package main\u000A');codeLines.push('import (\u000A \"embed\"\u000A)\u000A');codeLines.push('//go:embed folder/single_file.txt\u000Avar fileString string\u000A');codeLines.push('//go:embed folder/single_file.txt\u000Avar fileByte []byte\u000A');codeLines.push('//go:embed folder/single_file.txt\u000A//go:embed folder/*.hash\u000Avar folder embed.FS\u000A');codeLines.push('func main() {\u000A');codeLines.push(' print(fileString)\u000A print(string(fileByte))\u000A');codeLines.push(' content1, _ :\u003D folder.ReadFile(\"folder/file1.hash\")\u000A print(string(content1))\u000A');codeLines.push(' content2, _ :\u003D folder.ReadFile(\"folder/file2.hash\")\u000A print(string(content2))\u000A}\u000A');codeLines.push('');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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