Merge pull request alecthomas#313 from autarch/autarch/env-var-in-help

Add env var to --help output for flags and args

model.go

@@ -90,6 +90,13 @@ func (f *FlagModel) FormatPlaceHolder() string {
 	return strings.ToUpper(f.Name)
 }
 
+func (f *FlagModel) HelpWithEnvar() string {
+	if f.Envar == "" {
+		return f.Help
+	}
+	return fmt.Sprintf("%s ($%s)", f.Help, f.Envar)
+}
+
 type ArgGroupModel struct {
 	Args []*ArgModel
 }
@@ -114,6 +121,13 @@ func (a *ArgGroupModel) ArgSummary() string {
 	return strings.Join(out, " ")
 }
 
+func (a *ArgModel) HelpWithEnvar() string {
+	if a.Envar == "" {
+		return a.Help
+	}
+	return fmt.Sprintf("%s ($%s)", a.Help, a.Envar)
+}
+
 type ArgModel struct {
 	Name        string
 	Help        string

usage.go

@@ -136,7 +136,7 @@ func (a *Application) UsageForContextWithTemplate(context *ParseContext, indent
 			}
 			for _, flag := range f {
 				if !flag.Hidden {
-					rows = append(rows, [2]string{formatFlag(haveShort, flag), flag.Help})
+					rows = append(rows, [2]string{formatFlag(haveShort, flag), flag.HelpWithEnvar()})
 				}
 			}
 			return rows
@@ -172,7 +172,7 @@ func (a *Application) UsageForContextWithTemplate(context *ParseContext, indent
 					if !arg.Required {
 						s = "[" + s + "]"
 					}
-					rows = append(rows, [2]string{s, arg.Help})
+					rows = append(rows, [2]string{s, arg.HelpWithEnvar()})
 				}
 			}
 			return rows

usage_test.go

@@ -91,3 +91,16 @@ func TestCmdClause_HelpLong(t *testing.T) {
 	usage := buf.String()
 	assert.Equal(t, "long help text", usage)
 }
+
+func TestArgEnvVar(t *testing.T) {
+	var buf bytes.Buffer
+
+	a := New("test", "Test").Writer(&buf).Terminate(nil)
+	a.Arg("arg", "Enable arg").Envar("ARG").String()
+	a.Flag("flag", "Enable flag").Envar("FLAG").String()
+
+	a.Parse([]string{"command", "--help"})
+	usage := buf.String()
+	assert.Contains(t, usage, "($ARG)")
+	assert.Contains(t, usage, "($FLAG)")
+}