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package arg
import (
"fmt"
"io"
"os"
"reflect"
"strings"
)
// Usage prints usage information to stdout information and exits with status zero
func Usage(dest ...interface{}) {
if err := WriteUsage(os.Stdout, dest...); err != nil {
fmt.Println(err)
}
os.Exit(0)
}
// Fail prints usage information to stdout and exits with non-zero status
func Fail(msg string, dest ...interface{}) {
fmt.Println(msg)
if err := WriteUsage(os.Stdout, dest...); err != nil {
fmt.Println(err)
}
os.Exit(1)
}
// WriteUsage writes usage information to the given writer
func WriteUsage(w io.Writer, dest ...interface{}) error {
spec, err := extractSpec(dest...)
if err != nil {
return err
}
writeUsage(w, spec)
return nil
}
func synopsis(spec *spec, form string) string {
if spec.dest.Kind() == reflect.Bool {
return form
} else {
return form + " " + strings.ToUpper(spec.long)
}
}
// writeUsage writes usage information to the given writer
func writeUsage(w io.Writer, specs []*spec) {
var positionals, options []*spec
for _, spec := range specs {
if spec.positional {
positionals = append(positionals, spec)
} else {
options = append(options, spec)
}
}
fmt.Fprint(w, "usage: ")
// write the option component of the one-line usage message
for _, spec := range options {
if !spec.required {
fmt.Fprint(w, "[")
}
fmt.Fprint(w, synopsis(spec, "--"+spec.long))
if !spec.required {
fmt.Fprint(w, "]")
}
fmt.Fprint(w, " ")
}
// write the positional component of the one-line usage message
for _, spec := range positionals {
up := strings.ToUpper(spec.long)
if spec.multiple {
fmt.Fprintf(w, "[%s [%s ...]]", up, up)
} else {
fmt.Fprint(w, up)
}
fmt.Fprint(w, " ")
}
fmt.Fprint(w, "\n")
// write the list of positionals
if len(positionals) > 0 {
fmt.Fprint(w, "\npositional arguments:\n")
for _, spec := range positionals {
fmt.Fprintf(w, " %s\n", spec.long)
}
}
// write the list of options
if len(options) > 0 {
fmt.Fprint(w, "\noptions:\n")
const colWidth = 25
for _, spec := range options {
left := fmt.Sprint(synopsis(spec, "--"+spec.long))
if spec.short != "" {
left += ", " + fmt.Sprint(synopsis(spec, "-"+spec.short))
}
fmt.Print(left)
if spec.help != "" {
if len(left)+2 < colWidth {
fmt.Fprint(w, strings.Repeat(" ", colWidth-len(left)))
} else {
fmt.Fprint(w, "\n"+strings.Repeat(" ", colWidth))
}
fmt.Fprint(w, spec.help)
}
fmt.Fprint(w, "\n")
}
}
}
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