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.
6 Package flag implements command-line flag parsing.
10 Define flags using flag.String(), Bool(), Int(), etc.
12 This declares an integer flag, -flagname, stored in the pointer ip, with type *int.
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.
18 flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
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.
25 After all flags are defined, call
27 to parse the command line into the defined flags.
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)
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.
38 Command line flag syntax
40 The following forms are permitted:
44 -flag x // non-boolean flags only
45 One or two minus signs may be used; they are equivalent.
46 The last form is not permitted for boolean flags because the
47 meaning of the command
49 where * is a Unix shell wildcard, will change if there is a file
50 called 0, false, etc. You must use the -flag=false form to turn
53 Flag parsing stops just before the first non-flag argument
54 ("-" is a non-flag argument) or after the terminator "--".
56 Integer flags accept 1234, 0664, 0x1234 and may be negative.
58 1, 0, t, f, T, F, true, false, TRUE, FALSE, True, False
59 Duration flags accept any input valid for time.ParseDuration.
61 The default set of command-line flags is controlled by
62 top-level functions. The FlagSet type allows one to define
63 independent sets of flags, such as to implement subcommands
64 in a command-line interface. The methods of FlagSet are
65 analogous to the top-level functions for the command-line
82 // ErrHelp is the error returned if the -help or -h flag is invoked
83 // but no such flag is defined.
84 var ErrHelp
= errors
.New("flag: help requested")
89 func newBoolValue(val
bool, p
*bool) *boolValue
{
91 return (*boolValue
)(p
)
94 func (b
*boolValue
) Set(s
string) error
{
95 v
, err
:= strconv
.ParseBool(s
)
100 func (b
*boolValue
) Get() interface{} { return bool(*b
) }
102 func (b
*boolValue
) String() string { return strconv
.FormatBool(bool(*b
)) }
104 func (b
*boolValue
) IsBoolFlag() bool { return true }
106 // optional interface to indicate boolean flags that can be
107 // supplied without "=value" text
108 type boolFlag
interface {
116 func newIntValue(val
int, p
*int) *intValue
{
118 return (*intValue
)(p
)
121 func (i
*intValue
) Set(s
string) error
{
122 v
, err
:= strconv
.ParseInt(s
, 0, strconv
.IntSize
)
127 func (i
*intValue
) Get() interface{} { return int(*i
) }
129 func (i
*intValue
) String() string { return strconv
.Itoa(int(*i
)) }
132 type int64Value
int64
134 func newInt64Value(val
int64, p
*int64) *int64Value
{
136 return (*int64Value
)(p
)
139 func (i
*int64Value
) Set(s
string) error
{
140 v
, err
:= strconv
.ParseInt(s
, 0, 64)
145 func (i
*int64Value
) Get() interface{} { return int64(*i
) }
147 func (i
*int64Value
) String() string { return strconv
.FormatInt(int64(*i
), 10) }
152 func newUintValue(val
uint, p
*uint) *uintValue
{
154 return (*uintValue
)(p
)
157 func (i
*uintValue
) Set(s
string) error
{
158 v
, err
:= strconv
.ParseUint(s
, 0, strconv
.IntSize
)
163 func (i
*uintValue
) Get() interface{} { return uint(*i
) }
165 func (i
*uintValue
) String() string { return strconv
.FormatUint(uint64(*i
), 10) }
168 type uint64Value
uint64
170 func newUint64Value(val
uint64, p
*uint64) *uint64Value
{
172 return (*uint64Value
)(p
)
175 func (i
*uint64Value
) Set(s
string) error
{
176 v
, err
:= strconv
.ParseUint(s
, 0, 64)
181 func (i
*uint64Value
) Get() interface{} { return uint64(*i
) }
183 func (i
*uint64Value
) String() string { return strconv
.FormatUint(uint64(*i
), 10) }
186 type stringValue
string
188 func newStringValue(val
string, p
*string) *stringValue
{
190 return (*stringValue
)(p
)
193 func (s
*stringValue
) Set(val
string) error
{
194 *s
= stringValue(val
)
198 func (s
*stringValue
) Get() interface{} { return string(*s
) }
200 func (s
*stringValue
) String() string { return string(*s
) }
203 type float64Value
float64
205 func newFloat64Value(val
float64, p
*float64) *float64Value
{
207 return (*float64Value
)(p
)
210 func (f
*float64Value
) Set(s
string) error
{
211 v
, err
:= strconv
.ParseFloat(s
, 64)
216 func (f
*float64Value
) Get() interface{} { return float64(*f
) }
218 func (f
*float64Value
) String() string { return strconv
.FormatFloat(float64(*f
), 'g', -1, 64) }
220 // -- time.Duration Value
221 type durationValue time
.Duration
223 func newDurationValue(val time
.Duration
, p
*time
.Duration
) *durationValue
{
225 return (*durationValue
)(p
)
228 func (d
*durationValue
) Set(s
string) error
{
229 v
, err
:= time
.ParseDuration(s
)
230 *d
= durationValue(v
)
234 func (d
*durationValue
) Get() interface{} { return time
.Duration(*d
) }
236 func (d
*durationValue
) String() string { return (*time
.Duration
)(d
).String() }
238 // Value is the interface to the dynamic value stored in a flag.
239 // (The default value is represented as a string.)
241 // If a Value has an IsBoolFlag() bool method returning true,
242 // the command-line parser makes -name equivalent to -name=true
243 // rather than using the next command-line argument.
245 // Set is called once, in command line order, for each flag present.
246 // The flag package may call the String method with a zero-valued receiver,
247 // such as a nil pointer.
248 type Value
interface {
253 // Getter is an interface that allows the contents of a Value to be retrieved.
254 // It wraps the Value interface, rather than being part of it, because it
255 // appeared after Go 1 and its compatibility rules. All Value types provided
256 // by this package satisfy the Getter interface.
257 type Getter
interface {
262 // ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
263 type ErrorHandling
int
265 // These constants cause FlagSet.Parse to behave as described if the parse fails.
267 ContinueOnError ErrorHandling
= iota // Return a descriptive error.
268 ExitOnError
// Call os.Exit(2).
269 PanicOnError
// Call panic with a descriptive error.
272 // A FlagSet represents a set of defined flags. The zero value of a FlagSet
273 // has no name and has ContinueOnError error handling.
274 type FlagSet
struct {
275 // Usage is the function called when an error occurs while parsing flags.
276 // The field is a function (not a method) that may be changed to point to
277 // a custom error handler. What happens after Usage is called depends
278 // on the ErrorHandling setting; for the command line, this defaults
279 // to ExitOnError, which exits the program after calling Usage.
284 actual
map[string]*Flag
285 formal
map[string]*Flag
286 args
[]string // arguments after flags
287 errorHandling ErrorHandling
288 output io
.Writer
// nil means stderr; use out() accessor
291 // A Flag represents the state of a flag.
293 Name
string // name as it appears on command line
294 Usage
string // help message
295 Value Value
// value as set
296 DefValue
string // default value (as text); for usage message
299 // sortFlags returns the flags as a slice in lexicographical sorted order.
300 func sortFlags(flags
map[string]*Flag
) []*Flag
{
301 list
:= make(sort
.StringSlice
, len(flags
))
303 for _
, f
:= range flags
{
308 result
:= make([]*Flag
, len(list
))
309 for i
, name
:= range list
{
310 result
[i
] = flags
[name
]
315 // Output returns the destination for usage and error messages. os.Stderr is returned if
316 // output was not set or was set to nil.
317 func (f
*FlagSet
) Output() io
.Writer
{
324 // Name returns the name of the flag set.
325 func (f
*FlagSet
) Name() string {
329 // ErrorHandling returns the error handling behavior of the flag set.
330 func (f
*FlagSet
) ErrorHandling() ErrorHandling
{
331 return f
.errorHandling
334 // SetOutput sets the destination for usage and error messages.
335 // If output is nil, os.Stderr is used.
336 func (f
*FlagSet
) SetOutput(output io
.Writer
) {
340 // VisitAll visits the flags in lexicographical order, calling fn for each.
341 // It visits all flags, even those not set.
342 func (f
*FlagSet
) VisitAll(fn
func(*Flag
)) {
343 for _
, flag
:= range sortFlags(f
.formal
) {
348 // VisitAll visits the command-line flags in lexicographical order, calling
349 // fn for each. It visits all flags, even those not set.
350 func VisitAll(fn
func(*Flag
)) {
351 CommandLine
.VisitAll(fn
)
354 // Visit visits the flags in lexicographical order, calling fn for each.
355 // It visits only those flags that have been set.
356 func (f
*FlagSet
) Visit(fn
func(*Flag
)) {
357 for _
, flag
:= range sortFlags(f
.actual
) {
362 // Visit visits the command-line flags in lexicographical order, calling fn
363 // for each. It visits only those flags that have been set.
364 func Visit(fn
func(*Flag
)) {
365 CommandLine
.Visit(fn
)
368 // Lookup returns the Flag structure of the named flag, returning nil if none exists.
369 func (f
*FlagSet
) Lookup(name
string) *Flag
{
370 return f
.formal
[name
]
373 // Lookup returns the Flag structure of the named command-line flag,
374 // returning nil if none exists.
375 func Lookup(name
string) *Flag
{
376 return CommandLine
.formal
[name
]
379 // Set sets the value of the named flag.
380 func (f
*FlagSet
) Set(name
, value
string) error
{
381 flag
, ok
:= f
.formal
[name
]
383 return fmt
.Errorf("no such flag -%v", name
)
385 err
:= flag
.Value
.Set(value
)
390 f
.actual
= make(map[string]*Flag
)
392 f
.actual
[name
] = flag
396 // Set sets the value of the named command-line flag.
397 func Set(name
, value
string) error
{
398 return CommandLine
.Set(name
, value
)
401 // isZeroValue determines whether the string represents the zero
403 func isZeroValue(flag
*Flag
, value
string) bool {
404 // Build a zero value of the flag's Value type, and see if the
405 // result of calling its String method equals the value passed in.
406 // This works unless the Value type is itself an interface type.
407 typ
:= reflect
.TypeOf(flag
.Value
)
409 if typ
.Kind() == reflect
.Ptr
{
410 z
= reflect
.New(typ
.Elem())
412 z
= reflect
.Zero(typ
)
414 return value
== z
.Interface().(Value
).String()
417 // UnquoteUsage extracts a back-quoted name from the usage
418 // string for a flag and returns it and the un-quoted usage.
419 // Given "a `name` to show" it returns ("name", "a name to show").
420 // If there are no back quotes, the name is an educated guess of the
421 // type of the flag's value, or the empty string if the flag is boolean.
422 func UnquoteUsage(flag
*Flag
) (name
string, usage
string) {
423 // Look for a back-quoted name, but avoid the strings package.
425 for i
:= 0; i
< len(usage
); i
++ {
427 for j
:= i
+ 1; j
< len(usage
); j
++ {
429 name
= usage
[i
+1 : j
]
430 usage
= usage
[:i
] + name
+ usage
[j
+1:]
434 break // Only one back quote; use type name.
437 // No explicit name, so use type if we can find one.
439 switch flag
.Value
.(type) {
446 case *intValue
, *int64Value
:
450 case *uintValue
, *uint64Value
:
456 // PrintDefaults prints, to standard error unless configured otherwise, the
457 // default values of all defined command-line flags in the set. See the
458 // documentation for the global function PrintDefaults for more information.
459 func (f
*FlagSet
) PrintDefaults() {
460 f
.VisitAll(func(flag
*Flag
) {
461 s
:= fmt
.Sprintf(" -%s", flag
.Name
) // Two spaces before -; see next two comments.
462 name
, usage
:= UnquoteUsage(flag
)
466 // Boolean flags of one ASCII letter are so common we
467 // treat them specially, putting their usage on the same line.
468 if len(s
) <= 4 { // space, space, '-', 'x'.
471 // Four spaces before the tab triggers good alignment
472 // for both 4- and 8-space tab stops.
475 s
+= strings
.Replace(usage
, "\n", "\n \t", -1)
477 if !isZeroValue(flag
, flag
.DefValue
) {
478 if _
, ok
:= flag
.Value
.(*stringValue
); ok
{
479 // put quotes on the value
480 s
+= fmt
.Sprintf(" (default %q)", flag
.DefValue
)
482 s
+= fmt
.Sprintf(" (default %v)", flag
.DefValue
)
485 fmt
.Fprint(f
.Output(), s
, "\n")
489 // PrintDefaults prints, to standard error unless configured otherwise,
490 // a usage message showing the default settings of all defined
491 // command-line flags.
492 // For an integer valued flag x, the default output has the form
494 // usage-message-for-x (default 7)
495 // The usage message will appear on a separate line for anything but
496 // a bool flag with a one-byte name. For bool flags, the type is
497 // omitted and if the flag name is one byte the usage message appears
498 // on the same line. The parenthetical default is omitted if the
499 // default is the zero value for the type. The listed type, here int,
500 // can be changed by placing a back-quoted name in the flag's usage
501 // string; the first such item in the message is taken to be a parameter
502 // name to show in the message and the back quotes are stripped from
503 // the message when displayed. For instance, given
504 // flag.String("I", "", "search `directory` for include files")
505 // the output will be
507 // search directory for include files.
508 func PrintDefaults() {
509 CommandLine
.PrintDefaults()
512 // defaultUsage is the default function to print a usage message.
513 func (f
*FlagSet
) defaultUsage() {
515 fmt
.Fprintf(f
.Output(), "Usage:\n")
517 fmt
.Fprintf(f
.Output(), "Usage of %s:\n", f
.name
)
522 // NOTE: Usage is not just defaultUsage(CommandLine)
523 // because it serves (via godoc flag Usage) as the example
524 // for how to write your own usage function.
526 // Usage prints a usage message documenting all defined command-line flags
527 // to CommandLine's output, which by default is os.Stderr.
528 // It is called when an error occurs while parsing flags.
529 // The function is a variable that may be changed to point to a custom function.
530 // By default it prints a simple header and calls PrintDefaults; for details about the
531 // format of the output and how to control it, see the documentation for PrintDefaults.
532 // Custom usage functions may choose to exit the program; by default exiting
533 // happens anyway as the command line's error handling strategy is set to
536 fmt
.Fprintf(CommandLine
.Output(), "Usage of %s:\n", os
.Args
[0])
540 // NFlag returns the number of flags that have been set.
541 func (f
*FlagSet
) NFlag() int { return len(f
.actual
) }
543 // NFlag returns the number of command-line flags that have been set.
544 func NFlag() int { return len(CommandLine
.actual
) }
546 // Arg returns the i'th argument. Arg(0) is the first remaining argument
547 // after flags have been processed. Arg returns an empty string if the
548 // requested element does not exist.
549 func (f
*FlagSet
) Arg(i
int) string {
550 if i
< 0 || i
>= len(f
.args
) {
556 // Arg returns the i'th command-line argument. Arg(0) is the first remaining argument
557 // after flags have been processed. Arg returns an empty string if the
558 // requested element does not exist.
559 func Arg(i
int) string {
560 return CommandLine
.Arg(i
)
563 // NArg is the number of arguments remaining after flags have been processed.
564 func (f
*FlagSet
) NArg() int { return len(f
.args
) }
566 // NArg is the number of arguments remaining after flags have been processed.
567 func NArg() int { return len(CommandLine
.args
) }
569 // Args returns the non-flag arguments.
570 func (f
*FlagSet
) Args() []string { return f
.args
}
572 // Args returns the non-flag command-line arguments.
573 func Args() []string { return CommandLine
.args
}
575 // BoolVar defines a bool flag with specified name, default value, and usage string.
576 // The argument p points to a bool variable in which to store the value of the flag.
577 func (f
*FlagSet
) BoolVar(p
*bool, name
string, value
bool, usage
string) {
578 f
.Var(newBoolValue(value
, p
), name
, usage
)
581 // BoolVar defines a bool flag with specified name, default value, and usage string.
582 // The argument p points to a bool variable in which to store the value of the flag.
583 func BoolVar(p
*bool, name
string, value
bool, usage
string) {
584 CommandLine
.Var(newBoolValue(value
, p
), name
, usage
)
587 // Bool defines a bool flag with specified name, default value, and usage string.
588 // The return value is the address of a bool variable that stores the value of the flag.
589 func (f
*FlagSet
) Bool(name
string, value
bool, usage
string) *bool {
591 f
.BoolVar(p
, name
, value
, usage
)
595 // Bool defines a bool flag with specified name, default value, and usage string.
596 // The return value is the address of a bool variable that stores the value of the flag.
597 func Bool(name
string, value
bool, usage
string) *bool {
598 return CommandLine
.Bool(name
, value
, usage
)
601 // IntVar defines an int flag with specified name, default value, and usage string.
602 // The argument p points to an int variable in which to store the value of the flag.
603 func (f
*FlagSet
) IntVar(p
*int, name
string, value
int, usage
string) {
604 f
.Var(newIntValue(value
, p
), name
, usage
)
607 // IntVar defines an int flag with specified name, default value, and usage string.
608 // The argument p points to an int variable in which to store the value of the flag.
609 func IntVar(p
*int, name
string, value
int, usage
string) {
610 CommandLine
.Var(newIntValue(value
, p
), name
, usage
)
613 // Int defines an int flag with specified name, default value, and usage string.
614 // The return value is the address of an int variable that stores the value of the flag.
615 func (f
*FlagSet
) Int(name
string, value
int, usage
string) *int {
617 f
.IntVar(p
, name
, value
, usage
)
621 // Int defines an int flag with specified name, default value, and usage string.
622 // The return value is the address of an int variable that stores the value of the flag.
623 func Int(name
string, value
int, usage
string) *int {
624 return CommandLine
.Int(name
, value
, usage
)
627 // Int64Var defines an int64 flag with specified name, default value, and usage string.
628 // The argument p points to an int64 variable in which to store the value of the flag.
629 func (f
*FlagSet
) Int64Var(p
*int64, name
string, value
int64, usage
string) {
630 f
.Var(newInt64Value(value
, p
), name
, usage
)
633 // Int64Var defines an int64 flag with specified name, default value, and usage string.
634 // The argument p points to an int64 variable in which to store the value of the flag.
635 func Int64Var(p
*int64, name
string, value
int64, usage
string) {
636 CommandLine
.Var(newInt64Value(value
, p
), name
, usage
)
639 // Int64 defines an int64 flag with specified name, default value, and usage string.
640 // The return value is the address of an int64 variable that stores the value of the flag.
641 func (f
*FlagSet
) Int64(name
string, value
int64, usage
string) *int64 {
643 f
.Int64Var(p
, name
, value
, usage
)
647 // Int64 defines an int64 flag with specified name, default value, and usage string.
648 // The return value is the address of an int64 variable that stores the value of the flag.
649 func Int64(name
string, value
int64, usage
string) *int64 {
650 return CommandLine
.Int64(name
, value
, usage
)
653 // UintVar defines a uint flag with specified name, default value, and usage string.
654 // The argument p points to a uint variable in which to store the value of the flag.
655 func (f
*FlagSet
) UintVar(p
*uint, name
string, value
uint, usage
string) {
656 f
.Var(newUintValue(value
, p
), name
, usage
)
659 // UintVar defines a uint flag with specified name, default value, and usage string.
660 // The argument p points to a uint variable in which to store the value of the flag.
661 func UintVar(p
*uint, name
string, value
uint, usage
string) {
662 CommandLine
.Var(newUintValue(value
, p
), name
, usage
)
665 // Uint defines a uint flag with specified name, default value, and usage string.
666 // The return value is the address of a uint variable that stores the value of the flag.
667 func (f
*FlagSet
) Uint(name
string, value
uint, usage
string) *uint {
669 f
.UintVar(p
, name
, value
, usage
)
673 // Uint defines a uint flag with specified name, default value, and usage string.
674 // The return value is the address of a uint variable that stores the value of the flag.
675 func Uint(name
string, value
uint, usage
string) *uint {
676 return CommandLine
.Uint(name
, value
, usage
)
679 // Uint64Var defines a uint64 flag with specified name, default value, and usage string.
680 // The argument p points to a uint64 variable in which to store the value of the flag.
681 func (f
*FlagSet
) Uint64Var(p
*uint64, name
string, value
uint64, usage
string) {
682 f
.Var(newUint64Value(value
, p
), name
, usage
)
685 // Uint64Var defines a uint64 flag with specified name, default value, and usage string.
686 // The argument p points to a uint64 variable in which to store the value of the flag.
687 func Uint64Var(p
*uint64, name
string, value
uint64, usage
string) {
688 CommandLine
.Var(newUint64Value(value
, p
), name
, usage
)
691 // Uint64 defines a uint64 flag with specified name, default value, and usage string.
692 // The return value is the address of a uint64 variable that stores the value of the flag.
693 func (f
*FlagSet
) Uint64(name
string, value
uint64, usage
string) *uint64 {
695 f
.Uint64Var(p
, name
, value
, usage
)
699 // Uint64 defines a uint64 flag with specified name, default value, and usage string.
700 // The return value is the address of a uint64 variable that stores the value of the flag.
701 func Uint64(name
string, value
uint64, usage
string) *uint64 {
702 return CommandLine
.Uint64(name
, value
, usage
)
705 // StringVar defines a string flag with specified name, default value, and usage string.
706 // The argument p points to a string variable in which to store the value of the flag.
707 func (f
*FlagSet
) StringVar(p
*string, name
string, value
string, usage
string) {
708 f
.Var(newStringValue(value
, p
), name
, usage
)
711 // StringVar defines a string flag with specified name, default value, and usage string.
712 // The argument p points to a string variable in which to store the value of the flag.
713 func StringVar(p
*string, name
string, value
string, usage
string) {
714 CommandLine
.Var(newStringValue(value
, p
), name
, usage
)
717 // String defines a string flag with specified name, default value, and usage string.
718 // The return value is the address of a string variable that stores the value of the flag.
719 func (f
*FlagSet
) String(name
string, value
string, usage
string) *string {
721 f
.StringVar(p
, name
, value
, usage
)
725 // String defines a string flag with specified name, default value, and usage string.
726 // The return value is the address of a string variable that stores the value of the flag.
727 func String(name
string, value
string, usage
string) *string {
728 return CommandLine
.String(name
, value
, usage
)
731 // Float64Var defines a float64 flag with specified name, default value, and usage string.
732 // The argument p points to a float64 variable in which to store the value of the flag.
733 func (f
*FlagSet
) Float64Var(p
*float64, name
string, value
float64, usage
string) {
734 f
.Var(newFloat64Value(value
, p
), name
, usage
)
737 // Float64Var defines a float64 flag with specified name, default value, and usage string.
738 // The argument p points to a float64 variable in which to store the value of the flag.
739 func Float64Var(p
*float64, name
string, value
float64, usage
string) {
740 CommandLine
.Var(newFloat64Value(value
, p
), name
, usage
)
743 // Float64 defines a float64 flag with specified name, default value, and usage string.
744 // The return value is the address of a float64 variable that stores the value of the flag.
745 func (f
*FlagSet
) Float64(name
string, value
float64, usage
string) *float64 {
747 f
.Float64Var(p
, name
, value
, usage
)
751 // Float64 defines a float64 flag with specified name, default value, and usage string.
752 // The return value is the address of a float64 variable that stores the value of the flag.
753 func Float64(name
string, value
float64, usage
string) *float64 {
754 return CommandLine
.Float64(name
, value
, usage
)
757 // DurationVar defines a time.Duration flag with specified name, default value, and usage string.
758 // The argument p points to a time.Duration variable in which to store the value of the flag.
759 // The flag accepts a value acceptable to time.ParseDuration.
760 func (f
*FlagSet
) DurationVar(p
*time
.Duration
, name
string, value time
.Duration
, usage
string) {
761 f
.Var(newDurationValue(value
, p
), name
, usage
)
764 // DurationVar defines a time.Duration flag with specified name, default value, and usage string.
765 // The argument p points to a time.Duration variable in which to store the value of the flag.
766 // The flag accepts a value acceptable to time.ParseDuration.
767 func DurationVar(p
*time
.Duration
, name
string, value time
.Duration
, usage
string) {
768 CommandLine
.Var(newDurationValue(value
, p
), name
, usage
)
771 // Duration defines a time.Duration flag with specified name, default value, and usage string.
772 // The return value is the address of a time.Duration variable that stores the value of the flag.
773 // The flag accepts a value acceptable to time.ParseDuration.
774 func (f
*FlagSet
) Duration(name
string, value time
.Duration
, usage
string) *time
.Duration
{
775 p
:= new(time
.Duration
)
776 f
.DurationVar(p
, name
, value
, usage
)
780 // Duration defines a time.Duration flag with specified name, default value, and usage string.
781 // The return value is the address of a time.Duration variable that stores the value of the flag.
782 // The flag accepts a value acceptable to time.ParseDuration.
783 func Duration(name
string, value time
.Duration
, usage
string) *time
.Duration
{
784 return CommandLine
.Duration(name
, value
, usage
)
787 // Var defines a flag with the specified name and usage string. The type and
788 // value of the flag are represented by the first argument, of type Value, which
789 // typically holds a user-defined implementation of Value. For instance, the
790 // caller could create a flag that turns a comma-separated string into a slice
791 // of strings by giving the slice the methods of Value; in particular, Set would
792 // decompose the comma-separated string into the slice.
793 func (f
*FlagSet
) Var(value Value
, name
string, usage
string) {
794 // Remember the default value as a string; it won't change.
795 flag
:= &Flag
{name
, usage
, value
, value
.String()}
796 _
, alreadythere
:= f
.formal
[name
]
800 msg
= fmt
.Sprintf("flag redefined: %s", name
)
802 msg
= fmt
.Sprintf("%s flag redefined: %s", f
.name
, name
)
804 fmt
.Fprintln(f
.Output(), msg
)
805 panic(msg
) // Happens only if flags are declared with identical names
808 f
.formal
= make(map[string]*Flag
)
810 f
.formal
[name
] = flag
813 // Var defines a flag with the specified name and usage string. The type and
814 // value of the flag are represented by the first argument, of type Value, which
815 // typically holds a user-defined implementation of Value. For instance, the
816 // caller could create a flag that turns a comma-separated string into a slice
817 // of strings by giving the slice the methods of Value; in particular, Set would
818 // decompose the comma-separated string into the slice.
819 func Var(value Value
, name
string, usage
string) {
820 CommandLine
.Var(value
, name
, usage
)
823 // failf prints to standard error a formatted error and usage message and
824 // returns the error.
825 func (f
*FlagSet
) failf(format
string, a
...interface{}) error
{
826 err
:= fmt
.Errorf(format
, a
...)
827 fmt
.Fprintln(f
.Output(), err
)
832 // usage calls the Usage method for the flag set if one is specified,
833 // or the appropriate default usage function otherwise.
834 func (f
*FlagSet
) usage() {
842 // parseOne parses one flag. It reports whether a flag was seen.
843 func (f
*FlagSet
) parseOne() (bool, error
) {
844 if len(f
.args
) == 0 {
848 if len(s
) < 2 || s
[0] != '-' {
854 if len(s
) == 2 { // "--" terminates the flags
859 name
:= s
[numMinuses
:]
860 if len(name
) == 0 || name
[0] == '-' || name
[0] == '=' {
861 return false, f
.failf("bad flag syntax: %s", s
)
864 // it's a flag. does it have an argument?
868 for i
:= 1; i
< len(name
); i
++ { // equals cannot be first
877 flag
, alreadythere
:= m
[name
] // BUG
879 if name
== "help" || name
== "h" { // special case for nice help message.
881 return false, ErrHelp
883 return false, f
.failf("flag provided but not defined: -%s", name
)
886 if fv
, ok
:= flag
.Value
.(boolFlag
); ok
&& fv
.IsBoolFlag() { // special case: doesn't need an arg
888 if err
:= fv
.Set(value
); err
!= nil {
889 return false, f
.failf("invalid boolean value %q for -%s: %v", value
, name
, err
)
892 if err
:= fv
.Set("true"); err
!= nil {
893 return false, f
.failf("invalid boolean flag %s: %v", name
, err
)
897 // It must have a value, which might be the next argument.
898 if !hasValue
&& len(f
.args
) > 0 {
899 // value is the next arg
901 value
, f
.args
= f
.args
[0], f
.args
[1:]
904 return false, f
.failf("flag needs an argument: -%s", name
)
906 if err
:= flag
.Value
.Set(value
); err
!= nil {
907 return false, f
.failf("invalid value %q for flag -%s: %v", value
, name
, err
)
911 f
.actual
= make(map[string]*Flag
)
913 f
.actual
[name
] = flag
917 // Parse parses flag definitions from the argument list, which should not
918 // include the command name. Must be called after all flags in the FlagSet
919 // are defined and before flags are accessed by the program.
920 // The return value will be ErrHelp if -help or -h were set but not defined.
921 func (f
*FlagSet
) Parse(arguments
[]string) error
{
925 seen
, err
:= f
.parseOne()
932 switch f
.errorHandling
{
933 case ContinueOnError
:
944 // Parsed reports whether f.Parse has been called.
945 func (f
*FlagSet
) Parsed() bool {
949 // Parse parses the command-line flags from os.Args[1:]. Must be called
950 // after all flags are defined and before flags are accessed by the program.
952 // Ignore errors; CommandLine is set for ExitOnError.
953 CommandLine
.Parse(os
.Args
[1:])
956 // Parsed reports whether the command-line flags have been parsed.
958 return CommandLine
.Parsed()
961 // CommandLine is the default set of command-line flags, parsed from os.Args.
962 // The top-level functions such as BoolVar, Arg, and so on are wrappers for the
963 // methods of CommandLine.
964 var CommandLine
= NewFlagSet(os
.Args
[0], ExitOnError
)
967 // Override generic FlagSet default Usage with call to global Usage.
968 // Note: This is not CommandLine.Usage = Usage,
969 // because we want any eventual call to use any updated value of Usage,
970 // not the value it has when this line is run.
971 CommandLine
.Usage
= commandLineUsage
974 func commandLineUsage() {
978 // NewFlagSet returns a new, empty flag set with the specified name and
979 // error handling property. If the name is not empty, it will be printed
980 // in the default usage message and in error messages.
981 func NewFlagSet(name
string, errorHandling ErrorHandling
) *FlagSet
{
984 errorHandling
: errorHandling
,
986 f
.Usage
= f
.defaultUsage
990 // Init sets the name and error handling property for a flag set.
991 // By default, the zero FlagSet uses an empty name and the
992 // ContinueOnError error handling policy.
993 func (f
*FlagSet
) Init(name
string, errorHandling ErrorHandling
) {
995 f
.errorHandling
= errorHandling