Added the "dataname" tag

example_test.go

@@ -135,6 +135,42 @@ func Example_helpText() {
 	//   --help, -h             display this help and exit
 }
 
+// This example shows the usage string generated by go-arg with custom datanames
+func Example_helpDataname() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --help")
+
+	var args struct {
+		Input    string   `arg:"positional,dataname:DATAFILE"`
+		Output   []string `arg:"positional"`
+		Verbose  bool     `arg:"-v" help:"verbosity level"`
+		Dataset  string   `help:"dataset to use"`
+		Optimize int      `arg:"-O,help:optimization level,dataname:LEVEL"`
+		MaxJobs  int      `arg:"-j,help:maximum number of simultaneous jobs,dataname:N"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	osExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+
+	// Usage: example [--verbose] [--dataset DATASET] [--optimize LEVEL] [--maxjobs N] DATAFILE [OUTPUT [OUTPUT ...]]
+
+	// Positional arguments:
+	//   DATAFILE
+	//   OUTPUT
+
+	// Options:
+	//   --verbose, -v          verbosity level
+	//   --dataset DATASET      dataset to use
+	//   --optimize LEVEL, -O LEVEL
+	//                          optimization level
+	//   --maxjobs N, -j N      maximum number of simultanious jobs
+	//   --help, -h             display this help and exit
+}
+
 // This example shows the usage string generated by go-arg when using subcommands
 func Example_helpTextWithSubcommand() {
 	// These are the args you would pass in on the command line

parse.go

@@ -56,6 +56,7 @@ type spec struct {
 	env        string
 	boolean    bool
 	defaultVal string // default value for this option
+	dataname   string // name of the data in help
 }
 
 // command represents a named subcommand, or the top-level command
@@ -305,6 +306,8 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 					spec.required = true
 				case key == "positional":
 					spec.positional = true
+				case key == "dataname":
+					spec.dataname = value
 				case key == "separate":
 					spec.separate = true
 				case key == "help": // deprecated
@@ -342,6 +345,10 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			}
 		}
 
+		if spec.dataname == "" {
+			spec.dataname = strings.ToUpper(spec.long)
+		}
+
 		// Check whether this field is supported. It's good to do this here rather than
 		// wait until ParseValue because it means that a program with invalid argument
 		// fields will always fail regardless of whether the arguments it received

usage.go

@@ -76,17 +76,16 @@ func (p *Parser) writeUsageForCommand(w io.Writer, cmd *command) {
 	for _, spec := range positionals {
 		// prefix with a space
 		fmt.Fprint(w, " ")
-		up := strings.ToUpper(spec.long)
 		if spec.multiple {
 			if !spec.required {
 				fmt.Fprint(w, "[")
 			}
-			fmt.Fprintf(w, "%s [%s ...]", up, up)
+			fmt.Fprintf(w, "%s [%s ...]", spec.dataname, spec.dataname)
 			if !spec.required {
 				fmt.Fprint(w, "]")
 			}
 		} else {
-			fmt.Fprint(w, up)
+			fmt.Fprint(w, spec.dataname)
 		}
 	}
 	fmt.Fprint(w, "\n")
@@ -134,7 +133,7 @@ func (p *Parser) writeHelpForCommand(w io.Writer, cmd *command) {
 	if len(positionals) > 0 {
 		fmt.Fprint(w, "\nPositional arguments:\n")
 		for _, spec := range positionals {
-			printTwoCols(w, strings.ToUpper(spec.long), spec.help, "")
+			printTwoCols(w, spec.dataname, spec.help, "")
 		}
 	}
 
@@ -180,7 +179,7 @@ func synopsis(spec *spec, form string) string {
 	if spec.boolean {
 		return form
 	}
-	return form + " " + strings.ToUpper(spec.long)
+	return form + " " + spec.dataname
 }
 
 func ptrTo(s string) *string {