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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Text Templates</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'string-formatting';
}
if (e.key == "ArrowRight") {
window.location.href = 'regular-expressions';
}
}
</script>
<body>
<div class="example" id="text-templates">
<h2><a href="./">Go by Example</a>: Text Templates</h2>
<table>
<tr>
<td class="docs">
<p>Go offers built-in support for creating dynamic content or showing customized
output to the user with the <code>text/template</code> package. A sibling package
named <code>html/template</code> provides the same API but has additional security
features and should be used for generating HTML.</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/pDwkw1iMACF"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"os"</span>
<span class="s">"text/template"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>We can create a new template and parse its body from
a string.
Templates are a mix of static text and “actions” enclosed in
<code>{{...}}</code> that are used to dynamically insert content.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t1</span> <span class="o">:=</span> <span class="nx">template</span><span class="p">.</span><span class="nf">New</span><span class="p">(</span><span class="s">"t1"</span><span class="p">)</span>
<span class="nx">t1</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">t1</span><span class="p">.</span><span class="nf">Parse</span><span class="p">(</span><span class="s">"Value is {{.}}\n"</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>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Alternatively, we can use the <code>template.Must</code> function to
panic in case <code>Parse</code> returns an error. This is especially
useful for templates initialized in the global scope.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t1</span> <span class="p">=</span> <span class="nx">template</span><span class="p">.</span><span class="nf">Must</span><span class="p">(</span><span class="nx">t1</span><span class="p">.</span><span class="nf">Parse</span><span class="p">(</span><span class="s">"Value: {{.}}\n"</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>By “executing” the template we generate its text with
specific values for its actions. The <code>{{.}}</code> action is
replaced by the value passed as a parameter to <code>Execute</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t1</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="s">"some text"</span><span class="p">)</span>
<span class="nx">t1</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span>
<span class="nx">t1</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span>
<span class="s">"Go"</span><span class="p">,</span>
<span class="s">"Rust"</span><span class="p">,</span>
<span class="s">"C++"</span><span class="p">,</span>
<span class="s">"C#"</span><span class="p">,</span>
<span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Helper function we’ll use below.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">Create</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">name</span><span class="p">,</span> <span class="nx">t</span> <span class="kt">string</span><span class="p">)</span> <span class="o">*</span><span class="nx">template</span><span class="p">.</span><span class="nx">Template</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">template</span><span class="p">.</span><span class="nf">Must</span><span class="p">(</span><span class="nx">template</span><span class="p">.</span><span class="nf">New</span><span class="p">(</span><span class="nx">name</span><span class="p">).</span><span class="nf">Parse</span><span class="p">(</span><span class="nx">t</span><span class="p">))</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>If the data is a struct we can use the <code>{{.FieldName}}</code> action to access
its fields. The fields should be exported to be accessible when a
template is executing.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t2</span> <span class="o">:=</span> <span class="nf">Create</span><span class="p">(</span><span class="s">"t2"</span><span class="p">,</span> <span class="s">"Name: {{.Name}}\n"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">t2</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">Name</span> <span class="kt">string</span>
<span class="p">}{</span><span class="s">"Jane Doe"</span><span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>The same applies to maps; with maps there is no restriction on the
case of key names.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t2</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">string</span><span class="p">{</span>
<span class="s">"Name"</span><span class="p">:</span> <span class="s">"Mickey Mouse"</span><span class="p">,</span>
<span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>if/else provide conditional execution for templates. A value is considered
false if it’s the default value of a type, such as 0, an empty string,
nil pointer, etc.
This sample demonstrates another
feature of templates: using <code>-</code> in actions to trim whitespace.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t3</span> <span class="o">:=</span> <span class="nf">Create</span><span class="p">(</span><span class="s">"t3"</span><span class="p">,</span>
<span class="s">"{{if . -}} yes {{else -}} no {{end}}\n"</span><span class="p">)</span>
<span class="nx">t3</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="s">"not empty"</span><span class="p">)</span>
<span class="nx">t3</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span> <span class="s">""</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>range blocks let us loop through slices, arrays, maps or channels. Inside
the range block <code>{{.}}</code> is set to the current item of the iteration.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">t4</span> <span class="o">:=</span> <span class="nf">Create</span><span class="p">(</span><span class="s">"t4"</span><span class="p">,</span>
<span class="s">"Range: {{range .}}{{.}} {{end}}\n"</span><span class="p">)</span>
<span class="nx">t4</span><span class="p">.</span><span class="nf">Execute</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stdout</span><span class="p">,</span>
<span class="p">[]</span><span class="kt">string</span><span class="p">{</span>
<span class="s">"Go"</span><span class="p">,</span>
<span class="s">"Rust"</span><span class="p">,</span>
<span class="s">"C++"</span><span class="p">,</span>
<span class="s">"C#"</span><span class="p">,</span>
<span class="p">})</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run templates.go
<span class="go">Value: some text
</span><span class="go">Value: 5
</span><span class="go">Value: [Go Rust C++ C#]
</span><span class="go">Name: Jane Doe
</span><span class="go">Name: Mickey Mouse
</span><span class="go">yes
</span><span class="go">no
</span><span class="go">Range: Go Rust C++ C# </span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="regular-expressions">Regular Expressions</a>.
</p>
<p class="footer">
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>
</p>
</div>
<script>
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