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b350cb1 May 22, 2016
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// Example of use of the flags package.
package flags
import (
func Example() {
var opts struct {
// Slice of bool will append 'true' each time the option
// is encountered (can be set multiple times, like -vvv)
Verbose []bool `short:"v" long:"verbose" description:"Show verbose debug information"`
// Example of automatic marshalling to desired type (uint)
Offset uint `long:"offset" description:"Offset"`
// Example of a callback, called each time the option is found.
Call func(string) `short:"c" description:"Call phone number"`
// Example of a required flag
Name string `short:"n" long:"name" description:"A name" required:"true"`
// Example of a value name
File string `short:"f" long:"file" description:"A file" value-name:"FILE"`
// Example of a pointer
Ptr *int `short:"p" description:"A pointer to an integer"`
// Example of a slice of strings
StringSlice []string `short:"s" description:"A slice of strings"`
// Example of a slice of pointers
PtrSlice []*string `long:"ptrslice" description:"A slice of pointers to string"`
// Example of a map
IntMap map[string]int `long:"intmap" description:"A map from string to int"`
// Example of a filename (useful for completion)
Filename Filename `long:"filename" description:"A filename"`
// Example of positional arguments
Args struct {
ID string
Num int
Rest []string
} `positional-args:"yes" required:"yes"`
// Callback which will invoke callto:<argument> to call a number.
// Note that this works just on OS X (and probably only with
// Skype) but it shows the idea.
opts.Call = func(num string) {
cmd := exec.Command("open", "callto:"+num)
// Make some fake arguments to parse.
args := []string{
"-n", "Me",
"-p", "3",
"-s", "hello",
"-s", "world",
"--ptrslice", "hello",
"--ptrslice", "world",
"--intmap", "a:1",
"--intmap", "b:5",
"--filename", "hello.go",
// Parse flags from `args'. Note that here we use flags.ParseArgs for
// the sake of making a working example. Normally, you would simply use
// flags.Parse(&opts) which uses os.Args
_, err := ParseArgs(&opts, args)
if err != nil {
fmt.Printf("Verbosity: %v\n", opts.Verbose)
fmt.Printf("Offset: %d\n", opts.Offset)
fmt.Printf("Name: %s\n", opts.Name)
fmt.Printf("Ptr: %d\n", *opts.Ptr)
fmt.Printf("StringSlice: %v\n", opts.StringSlice)
fmt.Printf("PtrSlice: [%v %v]\n", *opts.PtrSlice[0], *opts.PtrSlice[1])
fmt.Printf("IntMap: [a:%v b:%v]\n", opts.IntMap["a"], opts.IntMap["b"])
fmt.Printf("Filename: %v\n", opts.Filename)
fmt.Printf("Args.ID: %s\n", opts.Args.ID)
fmt.Printf("Args.Num: %d\n", opts.Args.Num)
fmt.Printf("Args.Rest: %v\n", opts.Args.Rest)
// Output: Verbosity: [true true]
// Offset: 5
// Name: Me
// Ptr: 3
// StringSlice: [hello world]
// PtrSlice: [hello world]
// IntMap: [a:1 b:5]
// Filename: hello.go
// Args.ID: id
// Args.Num: 10
// Args.Rest: [remaining1 remaining2]