add env var defaults

Author: broothie

command_test.go

@@ -26,9 +26,9 @@ func ExampleNewCommand() {
 	// server v0.1.0: An http server.
 	//
 	// Usage:
-	//   server [flags] [sub-commands]
+	//   server [flags] [sub-command]
 	//
-	// Sub-commands:
+	// Sub-command:
 	//   proxy: Proxy requests to another server.
 	//
 	// Flags:

flag.go

@@ -11,16 +11,17 @@ import (
 const helpFlagName = "help"
 
 type Flag struct {
-	name         string
-	description  string
-	aliases      []string
-	shorts       []rune
-	isHelp       bool
-	isVersion    bool
-	isHidden     bool
-	isInherited  bool
-	parser       argParser
-	defaultValue any
+	name           string
+	description    string
+	aliases        []string
+	shorts         []rune
+	isHelp         bool
+	isVersion      bool
+	isHidden       bool
+	isInherited    bool
+	parser         argParser
+	defaultEnvName string
+	defaultValue   any
 
 	value any
 }

flag_options.go

@@ -1,6 +1,9 @@
 package cli
 
 import (
+	"os"
+
+	"github.com/bobg/errors"
 	"github.com/broothie/option"
 )
 
@@ -46,6 +49,7 @@ func SetFlagDefault[T Parseable](defaultValue T) option.Func[*Flag] {
 
 		flag.parser = argParser
 		flag.defaultValue = defaultValue
+		flag.defaultEnvName = ""
 		return flag, nil
 	}
 }
@@ -55,6 +59,22 @@ func SetFlagDefaultAndParser[T any](defaultValue T, argParser ArgParser[T]) opti
 	return func(flag *Flag) (*Flag, error) {
 		flag.parser = argParser
 		flag.defaultValue = defaultValue
+		flag.defaultEnvName = ""
+		return flag, nil
+	}
+}
+
+// SetFlagDefaultEnvAndParser sets the default value to that of the corresponding environment variable, and parser of the flag.
+func SetFlagDefaultEnvAndParser[T any](name string, argParser ArgParser[T]) option.Func[*Flag] {
+	return func(flag *Flag) (*Flag, error) {
+		defaultValue, err := argParser(os.Getenv(name))
+		if err != nil {
+			return nil, errors.Wrapf(err, "parsing value of $%s", name)
+		}
+
+		flag.parser = argParser
+		flag.defaultValue = defaultValue
+		flag.defaultEnvName = name
 		return flag, nil
 	}
 }

help.go

@@ -104,12 +104,17 @@ func (h helpContext) FlagTable() (string, error) {
 			shorts = fmt.Sprintf("-%s", string(flag.shorts))
 		}
 
+		defaultValueHelp := fmt.Sprintf("%q", fmt.Sprint(flag.defaultValue))
+		if flag.defaultEnvName != "" {
+			defaultValueHelp = fmt.Sprintf("$%s", flag.defaultEnvName)
+		}
+
 		return []string{
 			"",
 			strings.Join(longs, " "),
 			shorts,
 			flag.description,
-			fmt.Sprintf("(type: %T, default: %q)", flag.parser.Type(), fmt.Sprint(flag.defaultValue)),
+			fmt.Sprintf("(type: %T, default: %s)", flag.parser.Type(), defaultValueHelp),
 		}, true
 	}))
 }

help.tmpl

@@ -1,10 +1,10 @@
 {{.RootName}}{{ if .Version }} {{.Version}}{{ end }}: {{.RootDescription}}
 
 Usage:
-  {{.QualifiedName}} {{- if .Flags }} [flags]{{ end -}} {{- if .SubCommands }} [sub-commands]{{ end }}{{ if .ArgumentList }} {{.ArgumentList}}{{ end }}
+  {{.QualifiedName}} {{- if .Flags }} [flags]{{ end -}} {{- if .SubCommands }} [sub-command]{{ end }}{{ if .ArgumentList }} {{.ArgumentList}}{{ end }}
 
 {{ if .SubCommands -}}
-Sub-commands:
+Sub-command:
 {{.SubCommandsTable}}
 {{ end -}}
 

help_test.go

@@ -84,9 +84,9 @@ func TestCommand_renderHelp(t *testing.T) {
 				test v1.2.3-rc10: test command
 				
 				Usage:
-				  test [flags] [sub-commands]
+				  test [flags] [sub-command]
 				
-				Sub-commands:
+				Sub-command:
 				  some-command: some command
 				
 				Flags:

options_test.go

@@ -126,9 +126,9 @@ func ExampleAddSubCmd() {
 	// server: An http server.
 	//
 	// Usage:
-	//   server [sub-commands]
+	//   server [sub-command]
 	//
-	// Sub-commands:
+	// Sub-command:
 	//   start: Start the server
 }