flagext

README

flagext

Implementations of the flag.Value interface to extend the flag package

Documentation

Overview

Package flagext implements extensions to the standard flag package in the form of types that implement flag.Value

Index

• Constants
• func Choice(selection *string, choices ...string) flag.Value
• type Reader
  • func File(defaultPath string) Reader
  • func FileOrURL(defaultPath string, client *http.Client) Reader
  • func URL(defaultPath string, client *http.Client) Reader
• type Writer
  • func FileWriter(defaultPath string) Writer

Examples

• Choice (BadFlag)
• Choice (DefaultValue)
• Choice (GoodFlag)

Constants

const (
	// StdIO can be passed to File to set Stdin as the default
	StdIO = "-"
)

Functions

func Choice

func Choice(selection *string, choices ...string) flag.Value

Choice implements flag.Value. Pass directly into flag.Var. flag.Var sets selection to the value of a command line flag if it is among the choices. If the flag value is not among the choices, it returns an error.

Example (BadFlag)

package main

import (
	"flag"
	"fmt"
	"io/ioutil"

	"github.com/carlmjohnson/flagext"
)

func main() {
	fs := flag.NewFlagSet("ExampleChoice", flag.ContinueOnError)
	fs.SetOutput(ioutil.Discard)
	var mode string
	fs.Var(flagext.Choice(&mode, "a", "b"), "mode", "mode to run")

	err := fs.Parse([]string{"-mode", "c"})
	fmt.Println(err)
}

Output:

invalid value "c" for flag -mode: "c" not in a, b

Example (DefaultValue)

package main

import (
	"flag"
	"fmt"

	"github.com/carlmjohnson/flagext"
)

func main() {
	fs := flag.NewFlagSet("ExampleChoice", flag.ContinueOnError)
	mode := "none"
	fs.Var(flagext.Choice(&mode, "yes", "no"), "mode", "mode to run")
	fs.Parse([]string{})
	fmt.Println(mode)
}

Output:

none

Example (GoodFlag)

package main

import (
	"flag"
	"fmt"

	"github.com/carlmjohnson/flagext"
)

func main() {
	fs := flag.NewFlagSet("ExampleChoice", flag.ContinueOnError)
	var mode string
	fs.Var(flagext.Choice(&mode, "x", "y"), "mode", "mode to run")

	fs.Parse([]string{"-mode", "x"})
	fmt.Println(mode)
}

Output:

x

Types

type Reader

type Reader interface {
	io.ReadCloser
	flag.Getter
}

Reader is an io.ReadCloser that can be set as a flag.Value

func File

func File(defaultPath string) Reader

File returns an io.Reader that lazily loads a file set as a flag.Value. Pass StdIO ("-") to read from standard input.

func FileOrURL

func FileOrURL(defaultPath string, client *http.Client) Reader

FileOrURL is an io.Reader that lazily opens a URL or file path set as a flag.Value.

func URL

func URL(defaultPath string, client *http.Client) Reader

URL returns an io.Reader that lazily loads an HTTP(S) URL set as a flag.Value.

type Writer

type Writer interface {
	io.WriteCloser
	flag.Getter
}

Writer is an io.WriteCloser that can be set as a flag.Value

func FileWriter

func FileWriter(defaultPath string) Writer

FileWriter returns an io.WriteCloser that lazily os.Creates a file set as a flag.Value. Pass StdIO ("-") to write to standard output.