From 738fc184ef2421f504f3b98506f4a58574b56b82 Mon Sep 17 00:00:00 2001
From: Eli Bendersky <eliben@gmail.com>
Date: Tue, 4 Jun 2019 05:48:59 -0700
Subject: [PATCH] Subcommands example
---
examples.txt | 1 +
.../command-line-subcommands.go | 57 +++++
.../command-line-subcommands.hash | 2 +
.../command-line-subcommands.sh | 21 ++
public/command-line-flags | 2 +-
public/command-line-subcommands | 239 ++++++++++++++++++
public/index.html | 2 +
7 files changed, 323 insertions(+), 1 deletion(-)
create mode 100644 examples/command-line-subcommands/command-line-subcommands.go
create mode 100644 examples/command-line-subcommands/command-line-subcommands.hash
create mode 100644 examples/command-line-subcommands/command-line-subcommands.sh
create mode 100644 public/command-line-subcommands
diff --git a/examples.txt b/examples.txt
index 9e13b51..2c1539b 100644
--- a/examples.txt
+++ b/examples.txt
@@ -59,6 +59,7 @@ Writing Files
Line Filters
Command-Line Arguments
Command-Line Flags
+Command-Line Subcommands
Environment Variables
HTTP Clients
Spawning Processes
diff --git a/examples/command-line-subcommands/command-line-subcommands.go b/examples/command-line-subcommands/command-line-subcommands.go
new file mode 100644
index 0000000..132c9ec
--- /dev/null
+++ b/examples/command-line-subcommands/command-line-subcommands.go
@@ -0,0 +1,57 @@
+// Some command-line tools, like the `go` tool or `git`
+// have many *subcommands*, each with its own set of
+// flags. For example, `go build` and `go get` are two
+// different subcommands of the `go` tool.
+// The `flag` package lets us easily define simple
+// subcommands that have their own flags.
+
+package main
+
+import (
+ "flag"
+ "fmt"
+ "os"
+)
+
+func main() {
+
+ // We declare a subcommand using the `NewFlagSet`
+ // function, and proceed to define new flags specific
+ // for this subcommand.
+ fooCmd := flag.NewFlagSet("foo", flag.ExitOnError)
+ fooEnable := fooCmd.Bool("enable", false, "enable")
+ fooName := fooCmd.String("name", "", "name")
+
+ // For a different subcommand we can define different
+ // supported flags.
+ barCmd := flag.NewFlagSet("bar", flag.ExitOnError)
+ barLevel := barCmd.Int("level", 0, "level")
+
+ // The subcommand is expected as the first argument
+ // to the program.
+ if len(os.Args) < 2 {
+ fmt.Println("expected 'foo' or 'bar' subcommands")
+ os.Exit(1)
+ }
+
+ // Check which subcommand is invoked.
+ switch os.Args[1] {
+ case "foo":
+
+ // For every subcommand, we parse its own flags and
+ // have access to trailing positional arguments.
+ fooCmd.Parse(os.Args[2:])
+ fmt.Println("subcommand 'foo'")
+ fmt.Println(" enable:", *fooEnable)
+ fmt.Println(" name:", *fooName)
+ fmt.Println(" tail:", fooCmd.Args())
+ case "bar":
+ barCmd.Parse(os.Args[2:])
+ fmt.Println("subcommand 'bar'")
+ fmt.Println(" level:", *barLevel)
+ fmt.Println(" tail:", barCmd.Args())
+ default:
+ fmt.Println("expected 'foo' or 'bar' subcommands")
+ os.Exit(1)
+ }
+}
diff --git a/examples/command-line-subcommands/command-line-subcommands.hash b/examples/command-line-subcommands/command-line-subcommands.hash
new file mode 100644
index 0000000..b26ba5f
--- /dev/null
+++ b/examples/command-line-subcommands/command-line-subcommands.hash
@@ -0,0 +1,2 @@
+673d7811734cfd8f8f5bcb411e12def1e158cf0b
+V7xR3wMkquz
diff --git a/examples/command-line-subcommands/command-line-subcommands.sh b/examples/command-line-subcommands/command-line-subcommands.sh
new file mode 100644
index 0000000..a7cec9a
--- /dev/null
+++ b/examples/command-line-subcommands/command-line-subcommands.sh
@@ -0,0 +1,21 @@
+$ go build command-line-subcommands.go
+
+# First invoke the foo subcommand
+$ ./command-line-subcommands foo -enable -name=joe a1 a2
+subcommand 'foo'
+ enable: true
+ name: joe
+ tail: [a1 a2]
+
+# Now try bar
+$ ./command-line-subcommands bar -level 8 a1
+subcommand 'bar'
+ level: 8
+ tail: [a1]
+
+# But bar won't accept foo's flags
+$ ./command-line-subcommands bar -enable a1
+flag provided but not defined: -enable
+Usage of bar:
+ -level int
+ level
diff --git a/public/command-line-flags b/public/command-line-flags
index 47341d4..b2eb253 100644
--- a/public/command-line-flags
+++ b/public/command-line-flags
@@ -297,7 +297,7 @@ way to parameterize programs.</p>
<p class="next">
- Next example: <a href="environment-variables">Environment Variables</a>.
+ Next example: <a href="command-line-subcommands">Command-Line Subcommands</a>.
</p>
<p class="footer">
diff --git a/public/command-line-subcommands b/public/command-line-subcommands
new file mode 100644
index 0000000..190970c
--- /dev/null
+++ b/public/command-line-subcommands
@@ -0,0 +1,239 @@
+<!DOCTYPE html>
+<html>
+ <head>
+ <meta charset="utf-8">
+ <title>Go by Example: Command-Line Subcommands</title>
+ <link rel=stylesheet href="site.css">
+ </head>
+ <body>
+ <div class="example" id="command-line-subcommands">
+ <h2><a href="./">Go by Example</a>: Command-Line Subcommands</h2>
+
+ <table>
+
+ <tr>
+ <td class="docs">
+ <p>Some command-line tools, like the <code>go</code> tool or <code>git</code>
+have many <em>subcommands</em>, each with its own set of
+flags. For example, <code>go build</code> and <code>go get</code> are two
+different subcommands of the <code>go</code> tool.
+The <code>flag</code> package lets us easily define simple
+subcommands that have their own flags.</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/V7xR3wMkquz"><img title="Run code" class="run" src="data:image/png;base64,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" /></a>
+ <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
+ <span class="s">"flag"</span>
+ <span class="s">"fmt"</span>
+ <span class="s">"os"</span>
+<span class="p">)</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>We declare a subcommand using the <code>NewFlagSet</code>
+function, and proceed to define new flags specific
+for this subcommand.</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre> <span class="nx">fooCmd</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">NewFlagSet</span><span class="p">(</span><span class="s">"foo"</span><span class="p">,</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">ExitOnError</span><span class="p">)</span>
+ <span class="nx">fooEnable</span> <span class="o">:=</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nx">Bool</span><span class="p">(</span><span class="s">"enable"</span><span class="p">,</span> <span class="kc">false</span><span class="p">,</span> <span class="s">"enable"</span><span class="p">)</span>
+ <span class="nx">fooName</span> <span class="o">:=</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nx">String</span><span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">""</span><span class="p">,</span> <span class="s">"name"</span><span class="p">)</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>For a different subcommand we can define different
+supported flags.</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre> <span class="nx">barCmd</span> <span class="o">:=</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">NewFlagSet</span><span class="p">(</span><span class="s">"bar"</span><span class="p">,</span> <span class="nx">flag</span><span class="p">.</span><span class="nx">ExitOnError</span><span class="p">)</span>
+ <span class="nx">barLevel</span> <span class="o">:=</span> <span class="nx">barCmd</span><span class="p">.</span><span class="nx">Int</span><span class="p">(</span><span class="s">"level"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s">"level"</span><span class="p">)</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>The subcommand is expected as the first argument
+to the program.</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre> <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">)</span> <span class="p"><</span> <span class="mi">2</span> <span class="p">{</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"expected 'foo' or 'bar' subcommands"</span><span class="p">)</span>
+ <span class="nx">os</span><span class="p">.</span><span class="nx">Exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
+ <span class="p">}</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>Check which subcommand is invoked.</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre> <span class="k">switch</span> <span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">{</span>
+ <span class="k">case</span> <span class="s">"foo"</span><span class="p">:</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>For every subcommand, we parse its own flags and
+have access to trailing positional arguments.</p>
+
+ </td>
+ <td class="code">
+
+ <div class="highlight"><pre> <span class="nx">fooCmd</span><span class="p">.</span><span class="nx">Parse</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">[</span><span class="mi">2</span><span class="p">:])</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"subcommand 'foo'"</span><span class="p">)</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">" enable:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">fooEnable</span><span class="p">)</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">" name:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">fooName</span><span class="p">)</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">" tail:"</span><span class="p">,</span> <span class="nx">fooCmd</span><span class="p">.</span><span class="nx">Args</span><span class="p">())</span>
+ <span class="k">case</span> <span class="s">"bar"</span><span class="p">:</span>
+ <span class="nx">barCmd</span><span class="p">.</span><span class="nx">Parse</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Args</span><span class="p">[</span><span class="mi">2</span><span class="p">:])</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"subcommand 'bar'"</span><span class="p">)</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">" level:"</span><span class="p">,</span> <span class="o">*</span><span class="nx">barLevel</span><span class="p">)</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">" tail:"</span><span class="p">,</span> <span class="nx">barCmd</span><span class="p">.</span><span class="nx">Args</span><span class="p">())</span>
+ <span class="k">default</span><span class="p">:</span>
+ <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"expected 'foo' or 'bar' subcommands"</span><span class="p">)</span>
+ <span class="nx">os</span><span class="p">.</span><span class="nx">Exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
+ <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ </table>
+
+ <table>
+
+ <tr>
+ <td class="docs">
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre><span class="gp">$</span> go build command-line-subcommands.go
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>First invoke the foo subcommand</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre><span class="gp">$</span> ./command-line-subcommands foo -enable -name<span class="o">=</span>joe a1 a2
+<span class="go">subcommand 'foo'</span>
+<span class="go"> enable: true</span>
+<span class="go"> name: joe</span>
+<span class="go"> tail: [a1 a2]</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>Now try bar</p>
+
+ </td>
+ <td class="code leading">
+
+ <div class="highlight"><pre><span class="gp">$</span> ./command-line-subcommands bar -level <span class="m">8</span> a1
+<span class="go">subcommand 'bar'</span>
+<span class="go"> level: 8</span>
+<span class="go"> tail: [a1]</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td class="docs">
+ <p>But bar won’t accept foo’s flags</p>
+
+ </td>
+ <td class="code">
+
+ <div class="highlight"><pre><span class="gp">$</span> ./command-line-subcommands bar -enable a1
+<span class="go">flag provided but not defined: -enable</span>
+<span class="go">Usage of bar:</span>
+<span class="go"> -level int</span>
+<span class="go"> bar level</span>
+</pre></div>
+
+ </td>
+ </tr>
+
+ </table>
+
+
+ <p class="next">
+ Next example: <a href="environment-variables">Environment Variables</a>.
+ </p>
+
+ <p class="footer">
+ by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/command-line-subcommands">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
+ </p>
+ </div>
+ </body>
+</html>
diff --git a/public/index.html b/public/index.html
index 6b5727f..ca79490 100644
--- a/public/index.html
+++ b/public/index.html
@@ -145,6 +145,8 @@
<li><a href="command-line-flags">Command-Line Flags</a></li>
+ <li><a href="command-line-subcommands">Command-Line Subcommands</a></li>
+
<li><a href="environment-variables">Environment Variables</a></li>
<li><a href="http-clients">HTTP Clients</a></li>