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package goptions
import (
// HelpFunc is the signature of a function responsible for printing the help.
type HelpFunc func(w io.Writer, fs *FlagSet)
// Generates a new HelpFunc taking a `text/template.Template`-formatted
// string as an argument. The resulting template will be executed with the FlagSet
// as its data.
func NewTemplatedHelpFunc(tpl string) HelpFunc {
var once sync.Once
var t *template.Template
return func(w io.Writer, fs *FlagSet) {
once.Do(func() {
t = template.Must(template.New("helpTemplate").Parse(tpl))
err := t.Execute(w, fs)
if err != nil {
const (
_DEFAULT_HELP = `Usage: {{.Name}} [global options] {{with .Verbs}}<verb> [verb options]{{end}}
Global options:{{range .Flags}}
{{with .Short}}-{{.}},{{end}} {{with .Long}}--{{.}}{{end}} {{.Description}}{{with .DefaultValue}} (default: {{.}}){{end}}{{if .Obligatory}} (*){{end}}{{end}}
{{with .Verbs}}Verbs:{{range .}}
{{.Name}}:{{range .Flags}}
{{with .Short}}-{{.}},{{end}} {{with .Long}}--{{.}}{{end}} {{.Description}}{{with .DefaultValue}} (default: {{.}}){{end}}{{if .Obligatory}} (*){{end}}{{end}}{{end}}{{end}}
// DefaultHelpFunc is a HelpFunc which renders the default help template and pipes
// the output through a text/tabwriter.Writer before flushing it to the output.
func DefaultHelpFunc(w io.Writer, fs *FlagSet) {
tw := &tabwriter.Writer{}
tw.Init(w, 4, 4, 1, ' ', 0)
NewTemplatedHelpFunc(_DEFAULT_HELP)(tw, fs)
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