public/environment-variables

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Go by Example: Environment Variables</title>
    <link rel=stylesheet href="site.css">
  </head>
  <script>
      onkeydown = (e) => {
          
          if (e.key == "ArrowLeft") {
              window.location.href = 'command-line-subcommands';
          }
          
          
          if (e.key == "ArrowRight") {
              window.location.href = 'logging';
          }
          
      }
  </script>
  <body>
    <div class="example" id="environment-variables">
      <h2><a href="./">Go by Example</a>: Environment Variables</h2>
      
      <table>
        
        <tr>
          <td class="docs">
            <p><a href="https://en.wikipedia.org/wiki/Environment_variable">Environment variables</a>
are a universal mechanism for <a href="https://www.12factor.net/config">conveying configuration
information to Unix programs</a>.
Let&rsquo;s look at how to set, get, and list environment variables.</p>

          </td>
          <td class="code empty leading">
            
          
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            
          </td>
          <td class="code leading">
            <a href="https://go.dev/play/p/2jmwXM264NC"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            
          </td>
          <td class="code leading">
            
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="p">(</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;fmt&#34;</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;os&#34;</span>
</span></span><span class="line"><span class="cl">    <span class="s">&#34;strings&#34;</span>
</span></span><span class="line"><span class="cl"><span class="p">)</span></span></span></code></pre>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            
          </td>
          <td class="code leading">
            
          <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>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            <p>To set a key/value pair, use <code>os.Setenv</code>. To get a
value for a key, use <code>os.Getenv</code>. This will return
an empty string if the key isn&rsquo;t present in the
environment.</p>

          </td>
          <td class="code leading">
            
          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">os</span><span class="p">.</span><span class="nf">Setenv</span><span class="p">(</span><span class="s">&#34;FOO&#34;</span><span class="p">,</span> <span class="s">&#34;1&#34;</span><span class="p">)</span>
</span></span><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;FOO:&#34;</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Getenv</span><span class="p">(</span><span class="s">&#34;FOO&#34;</span><span class="p">))</span>
</span></span><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;BAR:&#34;</span><span class="p">,</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Getenv</span><span class="p">(</span><span class="s">&#34;BAR&#34;</span><span class="p">))</span></span></span></code></pre>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            <p>Use <code>os.Environ</code> to list all key/value pairs in the
environment. This returns a slice of strings in the
form <code>KEY=value</code>. You can <code>strings.SplitN</code> them to
get the key and value. Here we print all the keys.</p>

          </td>
          <td class="code">
            
          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">()</span>
</span></span><span class="line"><span class="cl">    <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="nf">Environ</span><span class="p">()</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl">        <span class="nx">pair</span> <span class="o">:=</span> <span class="nx">strings</span><span class="p">.</span><span class="nf">SplitN</span><span class="p">(</span><span class="nx">e</span><span class="p">,</span> <span class="s">&#34;=&#34;</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
</span></span><span class="line"><span class="cl">        <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">pair</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
</span></span><span class="line"><span class="cl">    <span class="p">}</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
          </td>
        </tr>
        
      </table>
      
      <table>
        
        <tr>
          <td class="docs">
            <p>Running the program shows that we pick up the value
for <code>FOO</code> that we set in the program, but that
<code>BAR</code> is empty.</p>

          </td>
          <td class="code leading">
            
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run environment-variables.go
</span></span><span class="line"><span class="cl"><span class="go">FOO: 1
</span></span></span><span class="line"><span class="cl"><span class="go">BAR: </span></span></span></code></pre>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            <p>The list of keys in the environment will depend on your
particular machine.</p>

          </td>
          <td class="code leading">
            
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="go">TERM_PROGRAM
</span></span></span><span class="line"><span class="cl"><span class="go">PATH
</span></span></span><span class="line"><span class="cl"><span class="go">SHELL
</span></span></span><span class="line"><span class="cl"><span class="go">...
</span></span></span><span class="line"><span class="cl"><span class="go">FOO</span></span></span></code></pre>
          </td>
        </tr>
        
        <tr>
          <td class="docs">
            <p>If we set <code>BAR</code> in the environment first, the running
program picks that value up.</p>

          </td>
          <td class="code">
            
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> BAR=2 go run environment-variables.go
</span></span><span class="line"><span class="cl"><span class="go">FOO: 1
</span></span></span><span class="line"><span class="cl"><span class="go">BAR: 2
</span></span></span><span class="line"><span class="cl"><span class="go">...</span></span></span></code></pre>
          </td>
        </tr>
        
      </table>
      
      
      <p class="next">
        Next example: <a href="logging">Logging</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>
      var codeLines = [];
      codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A    \"fmt\"\u000A    \"os\"\u000A    \"strings\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push('    os.Setenv(\"FOO\", \"1\")\u000A    fmt.Println(\"FOO:\", os.Getenv(\"FOO\"))\u000A    fmt.Println(\"BAR:\", os.Getenv(\"BAR\"))\u000A');codeLines.push('    fmt.Println()\u000A    for _, e :\u003D range os.Environ() {\u000A        pair :\u003D strings.SplitN(e, \"\u003D\", 2)\u000A        fmt.Println(pair[0])\u000A    }\u000A}\u000A');codeLines.push('');codeLines.push('');codeLines.push('');
    </script>
    <script src="site.js" async></script>
  </body>
</html>