646c8b39da
This bugfix implements correct way to calculate source sha1 hash, before it will changed, by propagation of unchanged sources. This commit will also include regenerated static files and *.hash files.
211 lines
7.9 KiB
Plaintext
Generated
211 lines
7.9 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: Exec'ing Processes</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 = 'spawning-processes';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'signals';
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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="execing-processes">
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<h2><a href="./">Go by Example</a>: Exec'ing Processes</h2>
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<table>
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<tr>
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<td class="docs">
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<p>In the previous example we looked at
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<a href="spawning-processes">spawning external processes</a>. We
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do this when we need an external process accessible to
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a running Go process. Sometimes we just want to
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completely replace the current Go process with another
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(perhaps non-Go) one. To do this we’ll use Go’s
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implementation of the classic
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<a href="http://en.wikipedia.org/wiki/Exec_(operating_system)"><code>exec</code></a>
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function.</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/T3da5euHejy"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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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="p">(</span>
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<span class="s">"os"</span>
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<span class="s">"os/exec"</span>
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<span class="s">"syscall"</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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<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>For our example we’ll exec <code>ls</code>. Go requires an
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absolute path to the binary we want to execute, so
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we’ll use <code>exec.LookPath</code> to find it (probably
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<code>/bin/ls</code>).</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">binary</span><span class="p">,</span> <span class="nx">lookErr</span> <span class="o">:=</span> <span class="nx">exec</span><span class="p">.</span><span class="nx">LookPath</span><span class="p">(</span><span class="s">"ls"</span><span class="p">)</span>
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<span class="k">if</span> <span class="nx">lookErr</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nb">panic</span><span class="p">(</span><span class="nx">lookErr</span><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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<tr>
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<td class="docs">
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<p><code>Exec</code> requires arguments in slice form (as
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apposed to one big string). We’ll give <code>ls</code> a few
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common arguments. Note that the first argument should
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be the program name.</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">args</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">"ls"</span><span class="p">,</span> <span class="s">"-a"</span><span class="p">,</span> <span class="s">"-l"</span><span class="p">,</span> <span class="s">"-h"</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><code>Exec</code> also needs a set of <a href="environment-variables">environment variables</a>
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to use. Here we just provide our current
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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">env</span> <span class="o">:=</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Environ</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>Here’s the actual <code>syscall.Exec</code> call. If this call is
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successful, the execution of our process will end
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here and be replaced by the <code>/bin/ls -a -l -h</code>
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process. If there is an error we’ll get a return
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value.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">execErr</span> <span class="o">:=</span> <span class="nx">syscall</span><span class="p">.</span><span class="nx">Exec</span><span class="p">(</span><span class="nx">binary</span><span class="p">,</span> <span class="nx">args</span><span class="p">,</span> <span class="nx">env</span><span class="p">)</span>
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<span class="k">if</span> <span class="nx">execErr</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nb">panic</span><span class="p">(</span><span class="nx">execErr</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>When we run our program it is replaced by <code>ls</code>.</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 execing-processes.go
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<span class="go">total 16</span>
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<span class="go">drwxr-xr-x 4 mark 136B Oct 3 16:29 .</span>
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<span class="go">drwxr-xr-x 91 mark 3.0K Oct 3 12:50 ..</span>
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<span class="go">-rw-r--r-- 1 mark 1.3K Oct 3 16:28 execing-processes.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>Note that Go does not offer a classic Unix <code>fork</code>
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function. Usually this isn’t an issue though, since
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starting goroutines, spawning processes, and exec’ing
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processes covers most use cases for <code>fork</code>.</p>
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</td>
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<td class="code empty">
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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="signals">Signals</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/execing-processes">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('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"os\"\u000A \"os/exec\"\u000A \"syscall\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' binary, lookErr := exec.LookPath(\"ls\")\u000A if lookErr != nil {\u000A panic(lookErr)\u000A }\u000A');codeLines.push(' args := []string{\"ls\", \"-a\", \"-l\", \"-h\"}\u000A');codeLines.push(' env := os.Environ()\u000A');codeLines.push(' execErr := syscall.Exec(binary, args, env)\u000A if execErr != nil {\u000A panic(execErr)\u000A }\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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