Optional long arguments

parse.go

@@ -48,6 +48,7 @@ func (p path) Child(f reflect.StructField) path {
 type spec struct {
 	dest        path
 	typ         reflect.Type
+	name        string // canonical name for the option
 	long        string
 	short       string
 	multiple    bool
@@ -280,6 +281,8 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			typ:  field.Type,
 		}
 
+		spec.name = spec.long
+
 		help, exists := field.Tag.Lookup("help")
 		if exists {
 			spec.help = help
@@ -308,6 +311,9 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 				errs = append(errs, fmt.Sprintf("%s.%s: too many hyphens", t.Name(), field.Name))
 			case strings.HasPrefix(key, "--"):
 				spec.long = key[2:]
+				if spec.long != "" {
+					spec.name = spec.long
+				}
 			case strings.HasPrefix(key, "-"):
 				if len(key) != 2 {
 					errs = append(errs, fmt.Sprintf("%s.%s: short arguments must be one character only",
@@ -364,7 +370,7 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 		if hasPlaceholder {
 			spec.placeholder = placeholder
 		} else {
-			spec.placeholder = strings.ToUpper(spec.long)
+			spec.placeholder = strings.ToUpper(spec.name)
 		}
 
 		// Check whether this field is supported. It's good to do this here rather than
@@ -617,13 +623,13 @@ func (p *Parser) process(args []string) error {
 		if spec.multiple {
 			err := setSlice(p.val(spec.dest), positionals, true)
 			if err != nil {
-				return fmt.Errorf("error processing %s: %v", spec.long, err)
+				return fmt.Errorf("error processing %s: %v", spec.name, err)
 			}
 			positionals = nil
 		} else {
 			err := scalar.ParseValue(p.val(spec.dest), positionals[0])
 			if err != nil {
-				return fmt.Errorf("error processing %s: %v", spec.long, err)
+				return fmt.Errorf("error processing %s: %v", spec.name, err)
 			}
 			positionals = positionals[1:]
 		}
@@ -638,8 +644,8 @@ func (p *Parser) process(args []string) error {
 			continue
 		}
 
-		name := spec.long
-		if !spec.positional {
+		name := spec.name
+		if spec.long != "" && !spec.positional {
 			name = "--" + spec.long
 		}
 

parse_test.go

@@ -231,6 +231,18 @@ func TestPlaceholder(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+func TestNoLongName(t *testing.T) {
+	var args struct {
+		ShortOnly string `arg:"-s,--"`
+		EnvOnly   string `arg:"--,env"`
+	}
+	setenv(t, "ENVONLY", "TestVal")
+	err := parse("-s TestVal2", &args)
+	assert.NoError(t, err)
+	assert.Equal(t, "TestVal", args.EnvOnly)
+	assert.Equal(t, "TestVal2", args.ShortOnly)
+}
+
 func TestCaseSensitive(t *testing.T) {
 	var args struct {
 		Lower bool `arg:"-v"`

usage.go

@@ -36,12 +36,15 @@ func (p *Parser) WriteUsage(w io.Writer) {
 
 // writeUsageForCommand writes usage information for the given subcommand
 func (p *Parser) writeUsageForCommand(w io.Writer, cmd *command) {
-	var positionals, options []*spec
+	var positionals, longOptions, shortOptions []*spec
 	for _, spec := range cmd.specs {
-		if spec.positional {
+		switch {
+		case spec.positional:
 			positionals = append(positionals, spec)
-		} else {
-			options = append(options, spec)
+		case spec.long != "":
+			longOptions = append(longOptions, spec)
+		case spec.short != "":
+			shortOptions = append(shortOptions, spec)
 		}
 	}
 
@@ -64,7 +67,19 @@ func (p *Parser) writeUsageForCommand(w io.Writer, cmd *command) {
 	}
 
 	// write the option component of the usage message
-	for _, spec := range options {
+	for _, spec := range shortOptions {
+		// prefix with a space
+		fmt.Fprint(w, " ")
+		if !spec.required {
+			fmt.Fprint(w, "[")
+		}
+		fmt.Fprint(w, synopsis(spec, "-"+spec.short))
+		if !spec.required {
+			fmt.Fprint(w, "]")
+		}
+	}
+
+	for _, spec := range longOptions {
 		// prefix with a space
 		fmt.Fprint(w, " ")
 		if !spec.required {
@@ -215,10 +230,14 @@ func (p *Parser) writeHelpForCommand(w io.Writer, cmd *command) {
 }
 
 func (p *Parser) printOption(w io.Writer, spec *spec) {
-	left := synopsis(spec, "--"+spec.long)
-	if spec.short != "" {
-		left += ", " + synopsis(spec, "-"+spec.short)
+	text := make([]string, 0, 2)
+	if spec.long != "" {
+		text = append(text, synopsis(spec, "--"+spec.long))
 	}
+	if spec.short != "" {
+		text = append(text, synopsis(spec, "-"+spec.short))
+	}
+	left := strings.Join(text, ", ")
 	printTwoCols(w, left, spec.help, spec.defaultVal, spec.env)
 }
 

usage_test.go

@@ -309,3 +309,22 @@ Global options:
 	p.WriteHelp(&help)
 	assert.Equal(t, expectedHelp, help.String())
 }
+
+func TestUsageWithOptionalLongNames(t *testing.T) {
+	expectedHelp := `Usage: example [-a PLACEHOLDER] -b SHORTONLY2
+
+Options:
+  -a PLACEHOLDER         some help [default: some val]
+  -b SHORTONLY2          some help2
+  --help, -h             display this help and exit
+`
+	var args struct {
+		ShortOnly  string `arg:"-a,--" help:"some help" default:"some val" placeholder:"PLACEHOLDER"`
+		ShortOnly2 string `arg:"-b,--,required" help:"some help2"`
+	}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	assert.NoError(t, err)
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp, help.String())
+}