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Source file src/flag/flag.go

     1	// Copyright 2009 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	/*
     6		Package flag implements command-line flag parsing.
     7	
     8		Usage:
     9	
    10		Define flags using flag.String(), Bool(), Int(), etc.
    11	
    12		This declares an integer flag, -flagname, stored in the pointer ip, with type *int.
    13			import "flag"
    14			var ip = flag.Int("flagname", 1234, "help message for flagname")
    15		If you like, you can bind the flag to a variable using the Var() functions.
    16			var flagvar int
    17			func init() {
    18				flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
    19			}
    20		Or you can create custom flags that satisfy the Value interface (with
    21		pointer receivers) and couple them to flag parsing by
    22			flag.Var(&flagVal, "name", "help message for flagname")
    23		For such flags, the default value is just the initial value of the variable.
    24	
    25		After all flags are defined, call
    26			flag.Parse()
    27		to parse the command line into the defined flags.
    28	
    29		Flags may then be used directly. If you're using the flags themselves,
    30		they are all pointers; if you bind to variables, they're values.
    31			fmt.Println("ip has value ", *ip)
    32			fmt.Println("flagvar has value ", flagvar)
    33	
    34		After parsing, the arguments following the flags are available as the
    35		slice flag.Args() or individually as flag.Arg(i).
    36		The arguments are indexed from 0 through flag.NArg()-1.
    37	
    38		Command line flag syntax:
    39			-flag
    40			-flag=x
    41			-flag x  // non-boolean flags only
    42		One or two minus signs may be used; they are equivalent.
    43		The last form is not permitted for boolean flags because the
    44		meaning of the command
    45			cmd -x *
    46		will change if there is a file called 0, false, etc.  You must
    47		use the -flag=false form to turn off a boolean flag.
    48	
    49		Flag parsing stops just before the first non-flag argument
    50		("-" is a non-flag argument) or after the terminator "--".
    51	
    52		Integer flags accept 1234, 0664, 0x1234 and may be negative.
    53		Boolean flags may be:
    54			1, 0, t, f, T, F, true, false, TRUE, FALSE, True, False
    55		Duration flags accept any input valid for time.ParseDuration.
    56	
    57		The default set of command-line flags is controlled by
    58		top-level functions.  The FlagSet type allows one to define
    59		independent sets of flags, such as to implement subcommands
    60		in a command-line interface. The methods of FlagSet are
    61		analogous to the top-level functions for the command-line
    62		flag set.
    63	*/
    64	package flag
    65	
    66	import (
    67		"errors"
    68		"fmt"
    69		"io"
    70		"os"
    71		"sort"
    72		"strconv"
    73		"time"
    74	)
    75	
    76	// ErrHelp is the error returned if the -help or -h flag is invoked
    77	// but no such flag is defined.
    78	var ErrHelp = errors.New("flag: help requested")
    79	
    80	// -- bool Value
    81	type boolValue bool
    82	
    83	func newBoolValue(val bool, p *bool) *boolValue {
    84		*p = val
    85		return (*boolValue)(p)
    86	}
    87	
    88	func (b *boolValue) Set(s string) error {
    89		v, err := strconv.ParseBool(s)
    90		*b = boolValue(v)
    91		return err
    92	}
    93	
    94	func (b *boolValue) Get() interface{} { return bool(*b) }
    95	
    96	func (b *boolValue) String() string { return fmt.Sprintf("%v", *b) }
    97	
    98	func (b *boolValue) IsBoolFlag() bool { return true }
    99	
   100	// optional interface to indicate boolean flags that can be
   101	// supplied without "=value" text
   102	type boolFlag interface {
   103		Value
   104		IsBoolFlag() bool
   105	}
   106	
   107	// -- int Value
   108	type intValue int
   109	
   110	func newIntValue(val int, p *int) *intValue {
   111		*p = val
   112		return (*intValue)(p)
   113	}
   114	
   115	func (i *intValue) Set(s string) error {
   116		v, err := strconv.ParseInt(s, 0, 64)
   117		*i = intValue(v)
   118		return err
   119	}
   120	
   121	func (i *intValue) Get() interface{} { return int(*i) }
   122	
   123	func (i *intValue) String() string { return fmt.Sprintf("%v", *i) }
   124	
   125	// -- int64 Value
   126	type int64Value int64
   127	
   128	func newInt64Value(val int64, p *int64) *int64Value {
   129		*p = val
   130		return (*int64Value)(p)
   131	}
   132	
   133	func (i *int64Value) Set(s string) error {
   134		v, err := strconv.ParseInt(s, 0, 64)
   135		*i = int64Value(v)
   136		return err
   137	}
   138	
   139	func (i *int64Value) Get() interface{} { return int64(*i) }
   140	
   141	func (i *int64Value) String() string { return fmt.Sprintf("%v", *i) }
   142	
   143	// -- uint Value
   144	type uintValue uint
   145	
   146	func newUintValue(val uint, p *uint) *uintValue {
   147		*p = val
   148		return (*uintValue)(p)
   149	}
   150	
   151	func (i *uintValue) Set(s string) error {
   152		v, err := strconv.ParseUint(s, 0, 64)
   153		*i = uintValue(v)
   154		return err
   155	}
   156	
   157	func (i *uintValue) Get() interface{} { return uint(*i) }
   158	
   159	func (i *uintValue) String() string { return fmt.Sprintf("%v", *i) }
   160	
   161	// -- uint64 Value
   162	type uint64Value uint64
   163	
   164	func newUint64Value(val uint64, p *uint64) *uint64Value {
   165		*p = val
   166		return (*uint64Value)(p)
   167	}
   168	
   169	func (i *uint64Value) Set(s string) error {
   170		v, err := strconv.ParseUint(s, 0, 64)
   171		*i = uint64Value(v)
   172		return err
   173	}
   174	
   175	func (i *uint64Value) Get() interface{} { return uint64(*i) }
   176	
   177	func (i *uint64Value) String() string { return fmt.Sprintf("%v", *i) }
   178	
   179	// -- string Value
   180	type stringValue string
   181	
   182	func newStringValue(val string, p *string) *stringValue {
   183		*p = val
   184		return (*stringValue)(p)
   185	}
   186	
   187	func (s *stringValue) Set(val string) error {
   188		*s = stringValue(val)
   189		return nil
   190	}
   191	
   192	func (s *stringValue) Get() interface{} { return string(*s) }
   193	
   194	func (s *stringValue) String() string { return fmt.Sprintf("%s", *s) }
   195	
   196	// -- float64 Value
   197	type float64Value float64
   198	
   199	func newFloat64Value(val float64, p *float64) *float64Value {
   200		*p = val
   201		return (*float64Value)(p)
   202	}
   203	
   204	func (f *float64Value) Set(s string) error {
   205		v, err := strconv.ParseFloat(s, 64)
   206		*f = float64Value(v)
   207		return err
   208	}
   209	
   210	func (f *float64Value) Get() interface{} { return float64(*f) }
   211	
   212	func (f *float64Value) String() string { return fmt.Sprintf("%v", *f) }
   213	
   214	// -- time.Duration Value
   215	type durationValue time.Duration
   216	
   217	func newDurationValue(val time.Duration, p *time.Duration) *durationValue {
   218		*p = val
   219		return (*durationValue)(p)
   220	}
   221	
   222	func (d *durationValue) Set(s string) error {
   223		v, err := time.ParseDuration(s)
   224		*d = durationValue(v)
   225		return err
   226	}
   227	
   228	func (d *durationValue) Get() interface{} { return time.Duration(*d) }
   229	
   230	func (d *durationValue) String() string { return (*time.Duration)(d).String() }
   231	
   232	// Value is the interface to the dynamic value stored in a flag.
   233	// (The default value is represented as a string.)
   234	//
   235	// If a Value has an IsBoolFlag() bool method returning true,
   236	// the command-line parser makes -name equivalent to -name=true
   237	// rather than using the next command-line argument.
   238	//
   239	// Set is called once, in command line order, for each flag present.
   240	type Value interface {
   241		String() string
   242		Set(string) error
   243	}
   244	
   245	// Getter is an interface that allows the contents of a Value to be retrieved.
   246	// It wraps the Value interface, rather than being part of it, because it
   247	// appeared after Go 1 and its compatibility rules. All Value types provided
   248	// by this package satisfy the Getter interface.
   249	type Getter interface {
   250		Value
   251		Get() interface{}
   252	}
   253	
   254	// ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
   255	type ErrorHandling int
   256	
   257	// These constants cause FlagSet.Parse to behave as described if the parse fails.
   258	const (
   259		ContinueOnError ErrorHandling = iota // Return a descriptive error.
   260		ExitOnError                          // Call os.Exit(2).
   261		PanicOnError                         // Call panic with a descriptive error.
   262	)
   263	
   264	// A FlagSet represents a set of defined flags.  The zero value of a FlagSet
   265	// has no name and has ContinueOnError error handling.
   266	type FlagSet struct {
   267		// Usage is the function called when an error occurs while parsing flags.
   268		// The field is a function (not a method) that may be changed to point to
   269		// a custom error handler.
   270		Usage func()
   271	
   272		name          string
   273		parsed        bool
   274		actual        map[string]*Flag
   275		formal        map[string]*Flag
   276		args          []string // arguments after flags
   277		errorHandling ErrorHandling
   278		output        io.Writer // nil means stderr; use out() accessor
   279	}
   280	
   281	// A Flag represents the state of a flag.
   282	type Flag struct {
   283		Name     string // name as it appears on command line
   284		Usage    string // help message
   285		Value    Value  // value as set
   286		DefValue string // default value (as text); for usage message
   287	}
   288	
   289	// sortFlags returns the flags as a slice in lexicographical sorted order.
   290	func sortFlags(flags map[string]*Flag) []*Flag {
   291		list := make(sort.StringSlice, len(flags))
   292		i := 0
   293		for _, f := range flags {
   294			list[i] = f.Name
   295			i++
   296		}
   297		list.Sort()
   298		result := make([]*Flag, len(list))
   299		for i, name := range list {
   300			result[i] = flags[name]
   301		}
   302		return result
   303	}
   304	
   305	func (f *FlagSet) out() io.Writer {
   306		if f.output == nil {
   307			return os.Stderr
   308		}
   309		return f.output
   310	}
   311	
   312	// SetOutput sets the destination for usage and error messages.
   313	// If output is nil, os.Stderr is used.
   314	func (f *FlagSet) SetOutput(output io.Writer) {
   315		f.output = output
   316	}
   317	
   318	// VisitAll visits the flags in lexicographical order, calling fn for each.
   319	// It visits all flags, even those not set.
   320	func (f *FlagSet) VisitAll(fn func(*Flag)) {
   321		for _, flag := range sortFlags(f.formal) {
   322			fn(flag)
   323		}
   324	}
   325	
   326	// VisitAll visits the command-line flags in lexicographical order, calling
   327	// fn for each.  It visits all flags, even those not set.
   328	func VisitAll(fn func(*Flag)) {
   329		CommandLine.VisitAll(fn)
   330	}
   331	
   332	// Visit visits the flags in lexicographical order, calling fn for each.
   333	// It visits only those flags that have been set.
   334	func (f *FlagSet) Visit(fn func(*Flag)) {
   335		for _, flag := range sortFlags(f.actual) {
   336			fn(flag)
   337		}
   338	}
   339	
   340	// Visit visits the command-line flags in lexicographical order, calling fn
   341	// for each.  It visits only those flags that have been set.
   342	func Visit(fn func(*Flag)) {
   343		CommandLine.Visit(fn)
   344	}
   345	
   346	// Lookup returns the Flag structure of the named flag, returning nil if none exists.
   347	func (f *FlagSet) Lookup(name string) *Flag {
   348		return f.formal[name]
   349	}
   350	
   351	// Lookup returns the Flag structure of the named command-line flag,
   352	// returning nil if none exists.
   353	func Lookup(name string) *Flag {
   354		return CommandLine.formal[name]
   355	}
   356	
   357	// Set sets the value of the named flag.
   358	func (f *FlagSet) Set(name, value string) error {
   359		flag, ok := f.formal[name]
   360		if !ok {
   361			return fmt.Errorf("no such flag -%v", name)
   362		}
   363		err := flag.Value.Set(value)
   364		if err != nil {
   365			return err
   366		}
   367		if f.actual == nil {
   368			f.actual = make(map[string]*Flag)
   369		}
   370		f.actual[name] = flag
   371		return nil
   372	}
   373	
   374	// Set sets the value of the named command-line flag.
   375	func Set(name, value string) error {
   376		return CommandLine.Set(name, value)
   377	}
   378	
   379	// isZeroValue guesses whether the string represents the zero
   380	// value for a flag. It is not accurate but in practice works OK.
   381	func isZeroValue(value string) bool {
   382		switch value {
   383		case "false":
   384			return true
   385		case "":
   386			return true
   387		case "0":
   388			return true
   389		}
   390		return false
   391	}
   392	
   393	// UnquoteUsage extracts a back-quoted name from the usage
   394	// string for a flag and returns it and the un-quoted usage.
   395	// Given "a `name` to show" it returns ("name", "a name to show").
   396	// If there are no back quotes, the name is an educated guess of the
   397	// type of the flag's value, or the empty string if the flag is boolean.
   398	func UnquoteUsage(flag *Flag) (name string, usage string) {
   399		// Look for a back-quoted name, but avoid the strings package.
   400		usage = flag.Usage
   401		for i := 0; i < len(usage); i++ {
   402			if usage[i] == '`' {
   403				for j := i + 1; j < len(usage); j++ {
   404					if usage[j] == '`' {
   405						name = usage[i+1 : j]
   406						usage = usage[:i] + name + usage[j+1:]
   407						return name, usage
   408					}
   409				}
   410				break // Only one back quote; use type name.
   411			}
   412		}
   413		// No explicit name, so use type if we can find one.
   414		name = "value"
   415		switch flag.Value.(type) {
   416		case boolFlag:
   417			name = ""
   418		case *durationValue:
   419			name = "duration"
   420		case *float64Value:
   421			name = "float"
   422		case *intValue, *int64Value:
   423			name = "int"
   424		case *stringValue:
   425			name = "string"
   426		case *uintValue, *uint64Value:
   427			name = "uint"
   428		}
   429		return
   430	}
   431	
   432	// PrintDefaults prints to standard error the default values of all
   433	// defined command-line flags in the set. See the documentation for
   434	// the global function PrintDefaults for more information.
   435	func (f *FlagSet) PrintDefaults() {
   436		f.VisitAll(func(flag *Flag) {
   437			s := fmt.Sprintf("  -%s", flag.Name) // Two spaces before -; see next two comments.
   438			name, usage := UnquoteUsage(flag)
   439			if len(name) > 0 {
   440				s += " " + name
   441			}
   442			// Boolean flags of one ASCII letter are so common we
   443			// treat them specially, putting their usage on the same line.
   444			if len(s) <= 4 { // space, space, '-', 'x'.
   445				s += "\t"
   446			} else {
   447				// Four spaces before the tab triggers good alignment
   448				// for both 4- and 8-space tab stops.
   449				s += "\n    \t"
   450			}
   451			s += usage
   452			if !isZeroValue(flag.DefValue) {
   453				if _, ok := flag.Value.(*stringValue); ok {
   454					// put quotes on the value
   455					s += fmt.Sprintf(" (default %q)", flag.DefValue)
   456				} else {
   457					s += fmt.Sprintf(" (default %v)", flag.DefValue)
   458				}
   459			}
   460			fmt.Fprint(f.out(), s, "\n")
   461		})
   462	}
   463	
   464	// PrintDefaults prints, to standard error unless configured otherwise,
   465	// a usage message showing the default settings of all defined
   466	// command-line flags.
   467	// For an integer valued flag x, the default output has the form
   468	//	-x int
   469	//		usage-message-for-x (default 7)
   470	// The usage message will appear on a separate line for anything but
   471	// a bool flag with a one-byte name. For bool flags, the type is
   472	// omitted and if the flag name is one byte the usage message appears
   473	// on the same line. The parenthetical default is omitted if the
   474	// default is the zero value for the type. The listed type, here int,
   475	// can be changed by placing a back-quoted name in the flag's usage
   476	// string; the first such item in the message is taken to be a parameter
   477	// name to show in the message and the back quotes are stripped from
   478	// the message when displayed. For instance, given
   479	//	flag.String("I", "", "search `directory` for include files")
   480	// the output will be
   481	//	-I directory
   482	//		search directory for include files.
   483	func PrintDefaults() {
   484		CommandLine.PrintDefaults()
   485	}
   486	
   487	// defaultUsage is the default function to print a usage message.
   488	func defaultUsage(f *FlagSet) {
   489		if f.name == "" {
   490			fmt.Fprintf(f.out(), "Usage:\n")
   491		} else {
   492			fmt.Fprintf(f.out(), "Usage of %s:\n", f.name)
   493		}
   494		f.PrintDefaults()
   495	}
   496	
   497	// NOTE: Usage is not just defaultUsage(CommandLine)
   498	// because it serves (via godoc flag Usage) as the example
   499	// for how to write your own usage function.
   500	
   501	// Usage prints to standard error a usage message documenting all defined command-line flags.
   502	// It is called when an error occurs while parsing flags.
   503	// The function is a variable that may be changed to point to a custom function.
   504	// By default it prints a simple header and calls PrintDefaults; for details about the
   505	// format of the output and how to control it, see the documentation for PrintDefaults.
   506	var Usage = func() {
   507		fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
   508		PrintDefaults()
   509	}
   510	
   511	// NFlag returns the number of flags that have been set.
   512	func (f *FlagSet) NFlag() int { return len(f.actual) }
   513	
   514	// NFlag returns the number of command-line flags that have been set.
   515	func NFlag() int { return len(CommandLine.actual) }
   516	
   517	// Arg returns the i'th argument.  Arg(0) is the first remaining argument
   518	// after flags have been processed. Arg returns an empty string if the
   519	// requested element does not exist.
   520	func (f *FlagSet) Arg(i int) string {
   521		if i < 0 || i >= len(f.args) {
   522			return ""
   523		}
   524		return f.args[i]
   525	}
   526	
   527	// Arg returns the i'th command-line argument.  Arg(0) is the first remaining argument
   528	// after flags have been processed. Arg returns an empty string if the
   529	// requested element does not exist.
   530	func Arg(i int) string {
   531		return CommandLine.Arg(i)
   532	}
   533	
   534	// NArg is the number of arguments remaining after flags have been processed.
   535	func (f *FlagSet) NArg() int { return len(f.args) }
   536	
   537	// NArg is the number of arguments remaining after flags have been processed.
   538	func NArg() int { return len(CommandLine.args) }
   539	
   540	// Args returns the non-flag arguments.
   541	func (f *FlagSet) Args() []string { return f.args }
   542	
   543	// Args returns the non-flag command-line arguments.
   544	func Args() []string { return CommandLine.args }
   545	
   546	// BoolVar defines a bool flag with specified name, default value, and usage string.
   547	// The argument p points to a bool variable in which to store the value of the flag.
   548	func (f *FlagSet) BoolVar(p *bool, name string, value bool, usage string) {
   549		f.Var(newBoolValue(value, p), name, usage)
   550	}
   551	
   552	// BoolVar defines a bool flag with specified name, default value, and usage string.
   553	// The argument p points to a bool variable in which to store the value of the flag.
   554	func BoolVar(p *bool, name string, value bool, usage string) {
   555		CommandLine.Var(newBoolValue(value, p), name, usage)
   556	}
   557	
   558	// Bool defines a bool flag with specified name, default value, and usage string.
   559	// The return value is the address of a bool variable that stores the value of the flag.
   560	func (f *FlagSet) Bool(name string, value bool, usage string) *bool {
   561		p := new(bool)
   562		f.BoolVar(p, name, value, usage)
   563		return p
   564	}
   565	
   566	// Bool defines a bool flag with specified name, default value, and usage string.
   567	// The return value is the address of a bool variable that stores the value of the flag.
   568	func Bool(name string, value bool, usage string) *bool {
   569		return CommandLine.Bool(name, value, usage)
   570	}
   571	
   572	// IntVar defines an int flag with specified name, default value, and usage string.
   573	// The argument p points to an int variable in which to store the value of the flag.
   574	func (f *FlagSet) IntVar(p *int, name string, value int, usage string) {
   575		f.Var(newIntValue(value, p), name, usage)
   576	}
   577	
   578	// IntVar defines an int flag with specified name, default value, and usage string.
   579	// The argument p points to an int variable in which to store the value of the flag.
   580	func IntVar(p *int, name string, value int, usage string) {
   581		CommandLine.Var(newIntValue(value, p), name, usage)
   582	}
   583	
   584	// Int defines an int flag with specified name, default value, and usage string.
   585	// The return value is the address of an int variable that stores the value of the flag.
   586	func (f *FlagSet) Int(name string, value int, usage string) *int {
   587		p := new(int)
   588		f.IntVar(p, name, value, usage)
   589		return p
   590	}
   591	
   592	// Int defines an int flag with specified name, default value, and usage string.
   593	// The return value is the address of an int variable that stores the value of the flag.
   594	func Int(name string, value int, usage string) *int {
   595		return CommandLine.Int(name, value, usage)
   596	}
   597	
   598	// Int64Var defines an int64 flag with specified name, default value, and usage string.
   599	// The argument p points to an int64 variable in which to store the value of the flag.
   600	func (f *FlagSet) Int64Var(p *int64, name string, value int64, usage string) {
   601		f.Var(newInt64Value(value, p), name, usage)
   602	}
   603	
   604	// Int64Var defines an int64 flag with specified name, default value, and usage string.
   605	// The argument p points to an int64 variable in which to store the value of the flag.
   606	func Int64Var(p *int64, name string, value int64, usage string) {
   607		CommandLine.Var(newInt64Value(value, p), name, usage)
   608	}
   609	
   610	// Int64 defines an int64 flag with specified name, default value, and usage string.
   611	// The return value is the address of an int64 variable that stores the value of the flag.
   612	func (f *FlagSet) Int64(name string, value int64, usage string) *int64 {
   613		p := new(int64)
   614		f.Int64Var(p, name, value, usage)
   615		return p
   616	}
   617	
   618	// Int64 defines an int64 flag with specified name, default value, and usage string.
   619	// The return value is the address of an int64 variable that stores the value of the flag.
   620	func Int64(name string, value int64, usage string) *int64 {
   621		return CommandLine.Int64(name, value, usage)
   622	}
   623	
   624	// UintVar defines a uint flag with specified name, default value, and usage string.
   625	// The argument p points to a uint variable in which to store the value of the flag.
   626	func (f *FlagSet) UintVar(p *uint, name string, value uint, usage string) {
   627		f.Var(newUintValue(value, p), name, usage)
   628	}
   629	
   630	// UintVar defines a uint flag with specified name, default value, and usage string.
   631	// The argument p points to a uint  variable in which to store the value of the flag.
   632	func UintVar(p *uint, name string, value uint, usage string) {
   633		CommandLine.Var(newUintValue(value, p), name, usage)
   634	}
   635	
   636	// Uint defines a uint flag with specified name, default value, and usage string.
   637	// The return value is the address of a uint  variable that stores the value of the flag.
   638	func (f *FlagSet) Uint(name string, value uint, usage string) *uint {
   639		p := new(uint)
   640		f.UintVar(p, name, value, usage)
   641		return p
   642	}
   643	
   644	// Uint defines a uint flag with specified name, default value, and usage string.
   645	// The return value is the address of a uint  variable that stores the value of the flag.
   646	func Uint(name string, value uint, usage string) *uint {
   647		return CommandLine.Uint(name, value, usage)
   648	}
   649	
   650	// Uint64Var defines a uint64 flag with specified name, default value, and usage string.
   651	// The argument p points to a uint64 variable in which to store the value of the flag.
   652	func (f *FlagSet) Uint64Var(p *uint64, name string, value uint64, usage string) {
   653		f.Var(newUint64Value(value, p), name, usage)
   654	}
   655	
   656	// Uint64Var defines a uint64 flag with specified name, default value, and usage string.
   657	// The argument p points to a uint64 variable in which to store the value of the flag.
   658	func Uint64Var(p *uint64, name string, value uint64, usage string) {
   659		CommandLine.Var(newUint64Value(value, p), name, usage)
   660	}
   661	
   662	// Uint64 defines a uint64 flag with specified name, default value, and usage string.
   663	// The return value is the address of a uint64 variable that stores the value of the flag.
   664	func (f *FlagSet) Uint64(name string, value uint64, usage string) *uint64 {
   665		p := new(uint64)
   666		f.Uint64Var(p, name, value, usage)
   667		return p
   668	}
   669	
   670	// Uint64 defines a uint64 flag with specified name, default value, and usage string.
   671	// The return value is the address of a uint64 variable that stores the value of the flag.
   672	func Uint64(name string, value uint64, usage string) *uint64 {
   673		return CommandLine.Uint64(name, value, usage)
   674	}
   675	
   676	// StringVar defines a string flag with specified name, default value, and usage string.
   677	// The argument p points to a string variable in which to store the value of the flag.
   678	func (f *FlagSet) StringVar(p *string, name string, value string, usage string) {
   679		f.Var(newStringValue(value, p), name, usage)
   680	}
   681	
   682	// StringVar defines a string flag with specified name, default value, and usage string.
   683	// The argument p points to a string variable in which to store the value of the flag.
   684	func StringVar(p *string, name string, value string, usage string) {
   685		CommandLine.Var(newStringValue(value, p), name, usage)
   686	}
   687	
   688	// String defines a string flag with specified name, default value, and usage string.
   689	// The return value is the address of a string variable that stores the value of the flag.
   690	func (f *FlagSet) String(name string, value string, usage string) *string {
   691		p := new(string)
   692		f.StringVar(p, name, value, usage)
   693		return p
   694	}
   695	
   696	// String defines a string flag with specified name, default value, and usage string.
   697	// The return value is the address of a string variable that stores the value of the flag.
   698	func String(name string, value string, usage string) *string {
   699		return CommandLine.String(name, value, usage)
   700	}
   701	
   702	// Float64Var defines a float64 flag with specified name, default value, and usage string.
   703	// The argument p points to a float64 variable in which to store the value of the flag.
   704	func (f *FlagSet) Float64Var(p *float64, name string, value float64, usage string) {
   705		f.Var(newFloat64Value(value, p), name, usage)
   706	}
   707	
   708	// Float64Var defines a float64 flag with specified name, default value, and usage string.
   709	// The argument p points to a float64 variable in which to store the value of the flag.
   710	func Float64Var(p *float64, name string, value float64, usage string) {
   711		CommandLine.Var(newFloat64Value(value, p), name, usage)
   712	}
   713	
   714	// Float64 defines a float64 flag with specified name, default value, and usage string.
   715	// The return value is the address of a float64 variable that stores the value of the flag.
   716	func (f *FlagSet) Float64(name string, value float64, usage string) *float64 {
   717		p := new(float64)
   718		f.Float64Var(p, name, value, usage)
   719		return p
   720	}
   721	
   722	// Float64 defines a float64 flag with specified name, default value, and usage string.
   723	// The return value is the address of a float64 variable that stores the value of the flag.
   724	func Float64(name string, value float64, usage string) *float64 {
   725		return CommandLine.Float64(name, value, usage)
   726	}
   727	
   728	// DurationVar defines a time.Duration flag with specified name, default value, and usage string.
   729	// The argument p points to a time.Duration variable in which to store the value of the flag.
   730	// The flag accepts a value acceptable to time.ParseDuration.
   731	func (f *FlagSet) DurationVar(p *time.Duration, name string, value time.Duration, usage string) {
   732		f.Var(newDurationValue(value, p), name, usage)
   733	}
   734	
   735	// DurationVar defines a time.Duration flag with specified name, default value, and usage string.
   736	// The argument p points to a time.Duration variable in which to store the value of the flag.
   737	// The flag accepts a value acceptable to time.ParseDuration.
   738	func DurationVar(p *time.Duration, name string, value time.Duration, usage string) {
   739		CommandLine.Var(newDurationValue(value, p), name, usage)
   740	}
   741	
   742	// Duration defines a time.Duration flag with specified name, default value, and usage string.
   743	// The return value is the address of a time.Duration variable that stores the value of the flag.
   744	// The flag accepts a value acceptable to time.ParseDuration.
   745	func (f *FlagSet) Duration(name string, value time.Duration, usage string) *time.Duration {
   746		p := new(time.Duration)
   747		f.DurationVar(p, name, value, usage)
   748		return p
   749	}
   750	
   751	// Duration defines a time.Duration flag with specified name, default value, and usage string.
   752	// The return value is the address of a time.Duration variable that stores the value of the flag.
   753	// The flag accepts a value acceptable to time.ParseDuration.
   754	func Duration(name string, value time.Duration, usage string) *time.Duration {
   755		return CommandLine.Duration(name, value, usage)
   756	}
   757	
   758	// Var defines a flag with the specified name and usage string. The type and
   759	// value of the flag are represented by the first argument, of type Value, which
   760	// typically holds a user-defined implementation of Value. For instance, the
   761	// caller could create a flag that turns a comma-separated string into a slice
   762	// of strings by giving the slice the methods of Value; in particular, Set would
   763	// decompose the comma-separated string into the slice.
   764	func (f *FlagSet) Var(value Value, name string, usage string) {
   765		// Remember the default value as a string; it won't change.
   766		flag := &Flag{name, usage, value, value.String()}
   767		_, alreadythere := f.formal[name]
   768		if alreadythere {
   769			var msg string
   770			if f.name == "" {
   771				msg = fmt.Sprintf("flag redefined: %s", name)
   772			} else {
   773				msg = fmt.Sprintf("%s flag redefined: %s", f.name, name)
   774			}
   775			fmt.Fprintln(f.out(), msg)
   776			panic(msg) // Happens only if flags are declared with identical names
   777		}
   778		if f.formal == nil {
   779			f.formal = make(map[string]*Flag)
   780		}
   781		f.formal[name] = flag
   782	}
   783	
   784	// Var defines a flag with the specified name and usage string. The type and
   785	// value of the flag are represented by the first argument, of type Value, which
   786	// typically holds a user-defined implementation of Value. For instance, the
   787	// caller could create a flag that turns a comma-separated string into a slice
   788	// of strings by giving the slice the methods of Value; in particular, Set would
   789	// decompose the comma-separated string into the slice.
   790	func Var(value Value, name string, usage string) {
   791		CommandLine.Var(value, name, usage)
   792	}
   793	
   794	// failf prints to standard error a formatted error and usage message and
   795	// returns the error.
   796	func (f *FlagSet) failf(format string, a ...interface{}) error {
   797		err := fmt.Errorf(format, a...)
   798		fmt.Fprintln(f.out(), err)
   799		f.usage()
   800		return err
   801	}
   802	
   803	// usage calls the Usage method for the flag set if one is specified,
   804	// or the appropriate default usage function otherwise.
   805	func (f *FlagSet) usage() {
   806		if f.Usage == nil {
   807			if f == CommandLine {
   808				Usage()
   809			} else {
   810				defaultUsage(f)
   811			}
   812		} else {
   813			f.Usage()
   814		}
   815	}
   816	
   817	// parseOne parses one flag. It reports whether a flag was seen.
   818	func (f *FlagSet) parseOne() (bool, error) {
   819		if len(f.args) == 0 {
   820			return false, nil
   821		}
   822		s := f.args[0]
   823		if len(s) == 0 || s[0] != '-' || len(s) == 1 {
   824			return false, nil
   825		}
   826		numMinuses := 1
   827		if s[1] == '-' {
   828			numMinuses++
   829			if len(s) == 2 { // "--" terminates the flags
   830				f.args = f.args[1:]
   831				return false, nil
   832			}
   833		}
   834		name := s[numMinuses:]
   835		if len(name) == 0 || name[0] == '-' || name[0] == '=' {
   836			return false, f.failf("bad flag syntax: %s", s)
   837		}
   838	
   839		// it's a flag. does it have an argument?
   840		f.args = f.args[1:]
   841		hasValue := false
   842		value := ""
   843		for i := 1; i < len(name); i++ { // equals cannot be first
   844			if name[i] == '=' {
   845				value = name[i+1:]
   846				hasValue = true
   847				name = name[0:i]
   848				break
   849			}
   850		}
   851		m := f.formal
   852		flag, alreadythere := m[name] // BUG
   853		if !alreadythere {
   854			if name == "help" || name == "h" { // special case for nice help message.
   855				f.usage()
   856				return false, ErrHelp
   857			}
   858			return false, f.failf("flag provided but not defined: -%s", name)
   859		}
   860	
   861		if fv, ok := flag.Value.(boolFlag); ok && fv.IsBoolFlag() { // special case: doesn't need an arg
   862			if hasValue {
   863				if err := fv.Set(value); err != nil {
   864					return false, f.failf("invalid boolean value %q for -%s: %v", value, name, err)
   865				}
   866			} else {
   867				if err := fv.Set("true"); err != nil {
   868					return false, f.failf("invalid boolean flag %s: %v", name, err)
   869				}
   870			}
   871		} else {
   872			// It must have a value, which might be the next argument.
   873			if !hasValue && len(f.args) > 0 {
   874				// value is the next arg
   875				hasValue = true
   876				value, f.args = f.args[0], f.args[1:]
   877			}
   878			if !hasValue {
   879				return false, f.failf("flag needs an argument: -%s", name)
   880			}
   881			if err := flag.Value.Set(value); err != nil {
   882				return false, f.failf("invalid value %q for flag -%s: %v", value, name, err)
   883			}
   884		}
   885		if f.actual == nil {
   886			f.actual = make(map[string]*Flag)
   887		}
   888		f.actual[name] = flag
   889		return true, nil
   890	}
   891	
   892	// Parse parses flag definitions from the argument list, which should not
   893	// include the command name.  Must be called after all flags in the FlagSet
   894	// are defined and before flags are accessed by the program.
   895	// The return value will be ErrHelp if -help or -h were set but not defined.
   896	func (f *FlagSet) Parse(arguments []string) error {
   897		f.parsed = true
   898		f.args = arguments
   899		for {
   900			seen, err := f.parseOne()
   901			if seen {
   902				continue
   903			}
   904			if err == nil {
   905				break
   906			}
   907			switch f.errorHandling {
   908			case ContinueOnError:
   909				return err
   910			case ExitOnError:
   911				os.Exit(2)
   912			case PanicOnError:
   913				panic(err)
   914			}
   915		}
   916		return nil
   917	}
   918	
   919	// Parsed reports whether f.Parse has been called.
   920	func (f *FlagSet) Parsed() bool {
   921		return f.parsed
   922	}
   923	
   924	// Parse parses the command-line flags from os.Args[1:].  Must be called
   925	// after all flags are defined and before flags are accessed by the program.
   926	func Parse() {
   927		// Ignore errors; CommandLine is set for ExitOnError.
   928		CommandLine.Parse(os.Args[1:])
   929	}
   930	
   931	// Parsed reports whether the command-line flags have been parsed.
   932	func Parsed() bool {
   933		return CommandLine.Parsed()
   934	}
   935	
   936	// CommandLine is the default set of command-line flags, parsed from os.Args.
   937	// The top-level functions such as BoolVar, Arg, and so on are wrappers for the
   938	// methods of CommandLine.
   939	var CommandLine = NewFlagSet(os.Args[0], ExitOnError)
   940	
   941	// NewFlagSet returns a new, empty flag set with the specified name and
   942	// error handling property.
   943	func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet {
   944		f := &FlagSet{
   945			name:          name,
   946			errorHandling: errorHandling,
   947		}
   948		return f
   949	}
   950	
   951	// Init sets the name and error handling property for a flag set.
   952	// By default, the zero FlagSet uses an empty name and the
   953	// ContinueOnError error handling policy.
   954	func (f *FlagSet) Init(name string, errorHandling ErrorHandling) {
   955		f.name = name
   956		f.errorHandling = errorHandling
   957	}
   958	

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