Improve spawning-process example with error-checking
This commit is contained in:
Eli Bendersky
parent
6b91c38bb3
commit
9deadb76ae
@ -17,10 +17,10 @@ func main() {
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// to represent this external process.
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dateCmd := exec.Command("date")
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// `.Output` is another helper that handles the common
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// case of running a command, waiting for it to finish,
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// and collecting its output. If there were no errors,
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// `dateOut` will hold bytes with the date info.
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// The `Output` method runs the command, waits for it
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// to finish and collects its standard output.
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// If there were no errors, `dateOut` will hold bytes
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// with the date info.
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dateOut, err := dateCmd.Output()
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if err != nil {
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panic(err)
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@ -28,6 +28,23 @@ func main() {
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fmt.Println("> date")
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fmt.Println(string(dateOut))
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// `Output` and other methods of `Command` will return
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// `*exec.Error` if there was a problem executing the
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// command (e.g. wrong path), and `*exec.ExitError`
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// if the command ran but exited with a non-zero return
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// code.
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_, err = exec.Command("date", "-x").Output()
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if err != nil {
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switch e := err.(type) {
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case *exec.Error:
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fmt.Println("failed executing:", err)
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case *exec.ExitError:
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fmt.Println("command exit rc =", e.ExitCode())
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default:
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panic(err)
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}
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}
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// Next we'll look at a slightly more involved case
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// where we pipe data to the external process on its
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// `stdin` and collect the results from its `stdout`.
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@ -1,2 +1,2 @@
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aaedc48f74409cef2b8e9ad624aa1c4639ce630d
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s-T7gxeD7hH
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5303cfb969de556a875db17972b4107b6f70ba10
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rmnQdR-dMWU
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@ -2,8 +2,11 @@
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# as if we had run them directly from the command-line.
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$ go run spawning-processes.go
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> date
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Wed Oct 10 09:53:11 PDT 2012
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Thu 05 May 2022 10:10:12 PM PDT
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# date doesn't have a `-x` flag so it will exit with
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# an error message and non-zero return code.
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command exited with rc = 1
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> grep hello
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hello grep
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49
public/spawning-processes
generated
49
public/spawning-processes
generated
@ -42,7 +42,7 @@ processes.</p>
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/s-T7gxeD7hH"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<a href="http://play.golang.org/p/rmnQdR-dMWU"><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"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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@ -92,10 +92,10 @@ to represent this external process.</p>
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<tr>
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<td class="docs">
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<p><code>.Output</code> is another helper that handles the common
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case of running a command, waiting for it to finish,
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and collecting its output. If there were no errors,
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<code>dateOut</code> will hold bytes with the date info.</p>
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<p>The <code>Output</code> method runs the command, waits for it
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to finish and collects its standard output.
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If there were no errors, <code>dateOut</code> will hold bytes
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with the date info.</p>
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</td>
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<td class="code leading">
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@ -111,6 +111,33 @@ and collecting its output. If there were no errors,
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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>Output</code> and other methods of <code>Command</code> will return
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<code>*exec.Error</code> if there was a problem executing the
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command (e.g. wrong path), and <code>*exec.ExitError</code>
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if the command ran but exited with a non-zero return
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code.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">_</span><span class="p">,</span> <span class="nx">err</span> <span class="p">=</span> <span class="nx">exec</span><span class="p">.</span><span class="nf">Command</span><span class="p">(</span><span class="s">"date"</span><span class="p">,</span> <span class="s">"-x"</span><span class="p">).</span><span class="nf">Output</span><span class="p">()</span>
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<span class="k">if</span> <span class="nx">err</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="k">switch</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">err</span><span class="p">.(</span><span class="kd">type</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">case</span> <span class="o">*</span><span class="nx">exec</span><span class="p">.</span><span class="nx">Error</span><span class="p">:</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"failed executing:"</span><span class="p">,</span> <span class="nx">err</span><span class="p">)</span>
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<span class="k">case</span> <span class="o">*</span><span class="nx">exec</span><span class="p">.</span><span class="nx">ExitError</span><span class="p">:</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"command exit rc ="</span><span class="p">,</span> <span class="nx">e</span><span class="p">.</span><span class="nf">ExitCode</span><span class="p">())</span>
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<span class="k">default</span><span class="p">:</span>
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<span class="nb">panic</span><span class="p">(</span><span class="nx">err</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>
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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>Next we’ll look at a slightly more involved case
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@ -206,17 +233,21 @@ as if we had run them directly from the command-line.</p>
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<pre class="chroma">
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<span class="gp">$</span> go run spawning-processes.go
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<span class="gp">></span> date
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<span class="go">Wed Oct 10 09:53:11 PDT 2012</span></pre>
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<span class="go">Thu 05 May 2022 10:10:12 PM PDT</span></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>date doesn’t have a <code>-x</code> flag so it will exit with
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an error message and non-zero return code.</p>
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="gp">></span> grep hello
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<pre class="chroma">
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<span class="go">command exited with rc = 1
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</span><span class="go"></span><span class="gp">></span> grep hello
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<span class="go">hello grep</span></pre>
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</td>
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</tr>
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@ -249,7 +280,7 @@ as if we had run them directly from the command-line.</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 \"fmt\"\u000A \"io\"\u000A \"os/exec\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' dateCmd :\u003D exec.Command(\"date\")\u000A');codeLines.push(' dateOut, err :\u003D dateCmd.Output()\u000A if err !\u003D nil {\u000A panic(err)\u000A }\u000A fmt.Println(\"\u003E date\")\u000A fmt.Println(string(dateOut))\u000A');codeLines.push(' grepCmd :\u003D exec.Command(\"grep\", \"hello\")\u000A');codeLines.push(' grepIn, _ :\u003D grepCmd.StdinPipe()\u000A grepOut, _ :\u003D grepCmd.StdoutPipe()\u000A grepCmd.Start()\u000A grepIn.Write([]byte(\"hello grep\\ngoodbye grep\"))\u000A grepIn.Close()\u000A grepBytes, _ :\u003D io.ReadAll(grepOut)\u000A grepCmd.Wait()\u000A');codeLines.push(' fmt.Println(\"\u003E grep hello\")\u000A fmt.Println(string(grepBytes))\u000A');codeLines.push(' lsCmd :\u003D exec.Command(\"bash\", \"-c\", \"ls -a -l -h\")\u000A lsOut, err :\u003D lsCmd.Output()\u000A if err !\u003D nil {\u000A panic(err)\u000A }\u000A fmt.Println(\"\u003E ls -a -l -h\")\u000A fmt.Println(string(lsOut))\u000A}\u000A');codeLines.push('');codeLines.push('');codeLines.push('');
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"io\"\u000A \"os/exec\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' dateCmd :\u003D exec.Command(\"date\")\u000A');codeLines.push(' dateOut, err :\u003D dateCmd.Output()\u000A if err !\u003D nil {\u000A panic(err)\u000A }\u000A fmt.Println(\"\u003E date\")\u000A fmt.Println(string(dateOut))\u000A');codeLines.push(' _, err \u003D exec.Command(\"date\", \"-x\").Output()\u000A if err !\u003D nil {\u000A switch e :\u003D err.(type) {\u000A case *exec.Error:\u000A fmt.Println(\"failed executing:\", err)\u000A case *exec.ExitError:\u000A fmt.Println(\"command exit rc \u003D\", e.ExitCode())\u000A default:\u000A panic(err)\u000A }\u000A }\u000A');codeLines.push(' grepCmd :\u003D exec.Command(\"grep\", \"hello\")\u000A');codeLines.push(' grepIn, _ :\u003D grepCmd.StdinPipe()\u000A grepOut, _ :\u003D grepCmd.StdoutPipe()\u000A grepCmd.Start()\u000A grepIn.Write([]byte(\"hello grep\\ngoodbye grep\"))\u000A grepIn.Close()\u000A grepBytes, _ :\u003D io.ReadAll(grepOut)\u000A grepCmd.Wait()\u000A');codeLines.push(' fmt.Println(\"\u003E grep hello\")\u000A fmt.Println(string(grepBytes))\u000A');codeLines.push(' lsCmd :\u003D exec.Command(\"bash\", \"-c\", \"ls -a -l -h\")\u000A lsOut, err :\u003D lsCmd.Output()\u000A if err !\u003D nil {\u000A panic(err)\u000A }\u000A fmt.Println(\"\u003E ls -a -l -h\")\u000A fmt.Println(string(lsOut))\u000A}\u000A');codeLines.push('');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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