Home | History | Annotate | Download | only in flag 
      1 // Copyright 2012 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 // These examples demonstrate more intricate uses of the flag package.
      6 package flag_test
      7 
      8 import (
      9 	"errors"
     10 	"flag"
     11 	"fmt"
     12 	"strings"
     13 	"time"
     14 )
     15 
     16 // Example 1: A single string flag called "species" with default value "gopher".
     17 var species = flag.String("species", "gopher", "the species we are studying")
     18 
     19 // Example 2: Two flags sharing a variable, so we can have a shorthand.
     20 // The order of initialization is undefined, so make sure both use the
     21 // same default value. They must be set up with an init function.
     22 var gopherType string
     23 
     24 func init() {
     25 	const (
     26 		defaultGopher = "pocket"
     27 		usage         = "the variety of gopher"
     28 	)
     29 	flag.StringVar(&gopherType, "gopher_type", defaultGopher, usage)
     30 	flag.StringVar(&gopherType, "g", defaultGopher, usage+" (shorthand)")
     31 }
     32 
     33 // Example 3: A user-defined flag type, a slice of durations.
     34 type interval []time.Duration
     35 
     36 // String is the method to format the flag's value, part of the flag.Value interface.
     37 // The String method's output will be used in diagnostics.
     38 func (i *interval) String() string {
     39 	return fmt.Sprint(*i)
     40 }
     41 
     42 // Set is the method to set the flag value, part of the flag.Value interface.
     43 // Set's argument is a string to be parsed to set the flag.
     44 // It's a comma-separated list, so we split it.
     45 func (i *interval) Set(value string) error {
     46 	// If we wanted to allow the flag to be set multiple times,
     47 	// accumulating values, we would delete this if statement.
     48 	// That would permit usages such as
     49 	//	-deltaT 10s -deltaT 15s
     50 	// and other combinations.
     51 	if len(*i) > 0 {
     52 		return errors.New("interval flag already set")
     53 	}
     54 	for _, dt := range strings.Split(value, ",") {
     55 		duration, err := time.ParseDuration(dt)
     56 		if err != nil {
     57 			return err
     58 		}
     59 		*i = append(*i, duration)
     60 	}
     61 	return nil
     62 }
     63 
     64 // Define a flag to accumulate durations. Because it has a special type,
     65 // we need to use the Var function and therefore create the flag during
     66 // init.
     67 
     68 var intervalFlag interval
     69 
     70 func init() {
     71 	// Tie the command-line flag to the intervalFlag variable and
     72 	// set a usage message.
     73 	flag.Var(&intervalFlag, "deltaT", "comma-separated list of intervals to use between events")
     74 }
     75 
     76 func Example() {
     77 	// All the interesting pieces are with the variables declared above, but
     78 	// to enable the flag package to see the flags defined there, one must
     79 	// execute, typically at the start of main (not init!):
     80 	//	flag.Parse()
     81 	// We don't run it here because this is not a main function and
     82 	// the testing suite has already parsed the flags.
     83 }
     84