189 lines
7.7 KiB
Plaintext
189 lines
7.7 KiB
Plaintext
<!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: Environment Variables</title>
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<link rel=stylesheet href="site.css">
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<div class="example" id="environment-variables">
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<h2><a href="./">Go by Example</a>: Environment Variables</h2>
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<table>
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<tr>
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<td class="docs">
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<p><a href="http://en.wikipedia.org/wiki/Environment_variable">Environment variables</a>
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are a universal mechanism for <a href="http://www.12factor.net/config">conveying configuration
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information to Unix programs</a>.
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Let’s look at how to set, get, and list environment variables.</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/CZJ4R_uu6Uu">
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<img title="Run code" class="run" src="data:image/png;base64,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" />
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</a>
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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="s">"os"</span>
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<span class="kn">import</span> <span class="s">"strings"</span>
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<span class="kn">import</span> <span class="s">"fmt"</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>To set a key/value pair, use <code>os.Setenv</code>. To get a
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value for a key, use <code>os.Getenv</code>. This will return
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an empty string if the key isn’t present in the
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environment.</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">os</span><span class="p">.</span><span class="nx">Setenv</span><span class="p">(</span><span class="s">"FOO"</span><span class="p">,</span> <span class="s">"1"</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">"FOO:"</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Getenv</span><span class="p">(</span><span class="s">"FOO"</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">"BAR:"</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Getenv</span><span class="p">(</span><span class="s">"BAR"</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>Use <code>os.Environ</code> to list all key/value pairs in the
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environment. This returns a slice of strings in the
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form <code>KEY=value</code>. You can <code>strings.Split</code> them to
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get the key and value. Here we print all the keys.</p>
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</td>
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<td class="code">
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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>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Environ</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">pair</span> <span class="o">:=</span> <span class="nx">strings</span><span class="p">.</span><span class="nx">Split</span><span class="p">(</span><span class="nx">e</span><span class="p">,</span> <span class="s">"="</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="nx">pair</span><span class="p">[</span><span class="mi">0</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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</table>
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<table>
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<tr>
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<td class="docs">
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<p>Running the program shows that we pick up the value
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for <code>FOO</code> that we set in the program, but that
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<code>BAR</code> is empty.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="gp">$</span> go run environment-variables.go
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<span class="go">FOO: 1</span>
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<span class="go">BAR: </span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The list of keys in the environment will depend on your
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particular machine.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="go">TERM_PROGRAM</span>
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<span class="go">PATH</span>
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<span class="go">SHELL</span>
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<span class="go">...</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>If we set <code>BAR</code> in the environment first, the running
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program picks that value up.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> <span class="nv">BAR</span><span class="o">=</span><span class="m">2</span> go run environment-variables.go
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<span class="go">FOO: 1</span>
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<span class="go">BAR: 2</span>
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<span class="go">...</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="http-clients">HTTP Clients</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/environment-variables">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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</body>
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</html>
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