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, -n, stored in the pointer nFlag, with type *int:
14 var nFlag = flag.Int("n", 1234, "help message for flag n")
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")
86 // errParse is returned by Set if a flag's value fails to parse, such as with an invalid integer for Int.
87 // It then gets wrapped through failf to provide more information.
88 var errParse
= errors
.New("parse error")
90 // errRange is returned by Set if a flag's value is out of range.
91 // It then gets wrapped through failf to provide more information.
92 var errRange
= errors
.New("value out of range")
94 func numError(err error
) error
{
95 ne
, ok
:= err
.(*strconv
.NumError
)
99 if ne
.Err
== strconv
.ErrSyntax
{
102 if ne
.Err
== strconv
.ErrRange
{
111 func newBoolValue(val
bool, p
*bool) *boolValue
{
113 return (*boolValue
)(p
)
116 func (b
*boolValue
) Set(s
string) error
{
117 v
, err
:= strconv
.ParseBool(s
)
125 func (b
*boolValue
) Get() any
{ return bool(*b
) }
127 func (b
*boolValue
) String() string { return strconv
.FormatBool(bool(*b
)) }
129 func (b
*boolValue
) IsBoolFlag() bool { return true }
131 // optional interface to indicate boolean flags that can be
132 // supplied without "=value" text
133 type boolFlag
interface {
141 func newIntValue(val
int, p
*int) *intValue
{
143 return (*intValue
)(p
)
146 func (i
*intValue
) Set(s
string) error
{
147 v
, err
:= strconv
.ParseInt(s
, 0, strconv
.IntSize
)
155 func (i
*intValue
) Get() any
{ return int(*i
) }
157 func (i
*intValue
) String() string { return strconv
.Itoa(int(*i
)) }
160 type int64Value
int64
162 func newInt64Value(val
int64, p
*int64) *int64Value
{
164 return (*int64Value
)(p
)
167 func (i
*int64Value
) Set(s
string) error
{
168 v
, err
:= strconv
.ParseInt(s
, 0, 64)
176 func (i
*int64Value
) Get() any
{ return int64(*i
) }
178 func (i
*int64Value
) String() string { return strconv
.FormatInt(int64(*i
), 10) }
183 func newUintValue(val
uint, p
*uint) *uintValue
{
185 return (*uintValue
)(p
)
188 func (i
*uintValue
) Set(s
string) error
{
189 v
, err
:= strconv
.ParseUint(s
, 0, strconv
.IntSize
)
197 func (i
*uintValue
) Get() any
{ return uint(*i
) }
199 func (i
*uintValue
) String() string { return strconv
.FormatUint(uint64(*i
), 10) }
202 type uint64Value
uint64
204 func newUint64Value(val
uint64, p
*uint64) *uint64Value
{
206 return (*uint64Value
)(p
)
209 func (i
*uint64Value
) Set(s
string) error
{
210 v
, err
:= strconv
.ParseUint(s
, 0, 64)
218 func (i
*uint64Value
) Get() any
{ return uint64(*i
) }
220 func (i
*uint64Value
) String() string { return strconv
.FormatUint(uint64(*i
), 10) }
223 type stringValue
string
225 func newStringValue(val
string, p
*string) *stringValue
{
227 return (*stringValue
)(p
)
230 func (s
*stringValue
) Set(val
string) error
{
231 *s
= stringValue(val
)
235 func (s
*stringValue
) Get() any
{ return string(*s
) }
237 func (s
*stringValue
) String() string { return string(*s
) }
240 type float64Value
float64
242 func newFloat64Value(val
float64, p
*float64) *float64Value
{
244 return (*float64Value
)(p
)
247 func (f
*float64Value
) Set(s
string) error
{
248 v
, err
:= strconv
.ParseFloat(s
, 64)
256 func (f
*float64Value
) Get() any
{ return float64(*f
) }
258 func (f
*float64Value
) String() string { return strconv
.FormatFloat(float64(*f
), 'g', -1, 64) }
260 // -- time.Duration Value
261 type durationValue time
.Duration
263 func newDurationValue(val time
.Duration
, p
*time
.Duration
) *durationValue
{
265 return (*durationValue
)(p
)
268 func (d
*durationValue
) Set(s
string) error
{
269 v
, err
:= time
.ParseDuration(s
)
273 *d
= durationValue(v
)
277 func (d
*durationValue
) Get() any
{ return time
.Duration(*d
) }
279 func (d
*durationValue
) String() string { return (*time
.Duration
)(d
).String() }
281 type funcValue
func(string) error
283 func (f funcValue
) Set(s
string) error
{ return f(s
) }
285 func (f funcValue
) String() string { return "" }
287 // Value is the interface to the dynamic value stored in a flag.
288 // (The default value is represented as a string.)
290 // If a Value has an IsBoolFlag() bool method returning true,
291 // the command-line parser makes -name equivalent to -name=true
292 // rather than using the next command-line argument.
294 // Set is called once, in command line order, for each flag present.
295 // The flag package may call the String method with a zero-valued receiver,
296 // such as a nil pointer.
297 type Value
interface {
302 // Getter is an interface that allows the contents of a Value to be retrieved.
303 // It wraps the Value interface, rather than being part of it, because it
304 // appeared after Go 1 and its compatibility rules. All Value types provided
305 // by this package satisfy the Getter interface, except the type used by Func.
306 type Getter
interface {
311 // ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
312 type ErrorHandling
int
314 // These constants cause FlagSet.Parse to behave as described if the parse fails.
316 ContinueOnError ErrorHandling
= iota // Return a descriptive error.
317 ExitOnError
// Call os.Exit(2) or for -h/-help Exit(0).
318 PanicOnError
// Call panic with a descriptive error.
321 // A FlagSet represents a set of defined flags. The zero value of a FlagSet
322 // has no name and has ContinueOnError error handling.
324 // Flag names must be unique within a FlagSet. An attempt to define a flag whose
325 // name is already in use will cause a panic.
326 type FlagSet
struct {
327 // Usage is the function called when an error occurs while parsing flags.
328 // The field is a function (not a method) that may be changed to point to
329 // a custom error handler. What happens after Usage is called depends
330 // on the ErrorHandling setting; for the command line, this defaults
331 // to ExitOnError, which exits the program after calling Usage.
336 actual
map[string]*Flag
337 formal
map[string]*Flag
338 args
[]string // arguments after flags
339 errorHandling ErrorHandling
340 output io
.Writer
// nil means stderr; use Output() accessor
343 // A Flag represents the state of a flag.
345 Name
string // name as it appears on command line
346 Usage
string // help message
347 Value Value
// value as set
348 DefValue
string // default value (as text); for usage message
351 // sortFlags returns the flags as a slice in lexicographical sorted order.
352 func sortFlags(flags
map[string]*Flag
) []*Flag
{
353 result
:= make([]*Flag
, len(flags
))
355 for _
, f
:= range flags
{
359 sort
.Slice(result
, func(i
, j
int) bool {
360 return result
[i
].Name
< result
[j
].Name
365 // Output returns the destination for usage and error messages. os.Stderr is returned if
366 // output was not set or was set to nil.
367 func (f
*FlagSet
) Output() io
.Writer
{
374 // Name returns the name of the flag set.
375 func (f
*FlagSet
) Name() string {
379 // ErrorHandling returns the error handling behavior of the flag set.
380 func (f
*FlagSet
) ErrorHandling() ErrorHandling
{
381 return f
.errorHandling
384 // SetOutput sets the destination for usage and error messages.
385 // If output is nil, os.Stderr is used.
386 func (f
*FlagSet
) SetOutput(output io
.Writer
) {
390 // VisitAll visits the flags in lexicographical order, calling fn for each.
391 // It visits all flags, even those not set.
392 func (f
*FlagSet
) VisitAll(fn
func(*Flag
)) {
393 for _
, flag
:= range sortFlags(f
.formal
) {
398 // VisitAll visits the command-line flags in lexicographical order, calling
399 // fn for each. It visits all flags, even those not set.
400 func VisitAll(fn
func(*Flag
)) {
401 CommandLine
.VisitAll(fn
)
404 // Visit visits the flags in lexicographical order, calling fn for each.
405 // It visits only those flags that have been set.
406 func (f
*FlagSet
) Visit(fn
func(*Flag
)) {
407 for _
, flag
:= range sortFlags(f
.actual
) {
412 // Visit visits the command-line flags in lexicographical order, calling fn
413 // for each. It visits only those flags that have been set.
414 func Visit(fn
func(*Flag
)) {
415 CommandLine
.Visit(fn
)
418 // Lookup returns the Flag structure of the named flag, returning nil if none exists.
419 func (f
*FlagSet
) Lookup(name
string) *Flag
{
420 return f
.formal
[name
]
423 // Lookup returns the Flag structure of the named command-line flag,
424 // returning nil if none exists.
425 func Lookup(name
string) *Flag
{
426 return CommandLine
.formal
[name
]
429 // Set sets the value of the named flag.
430 func (f
*FlagSet
) Set(name
, value
string) error
{
431 flag
, ok
:= f
.formal
[name
]
433 return fmt
.Errorf("no such flag -%v", name
)
435 err
:= flag
.Value
.Set(value
)
440 f
.actual
= make(map[string]*Flag
)
442 f
.actual
[name
] = flag
446 // Set sets the value of the named command-line flag.
447 func Set(name
, value
string) error
{
448 return CommandLine
.Set(name
, value
)
451 // isZeroValue determines whether the string represents the zero
453 func isZeroValue(flag
*Flag
, value
string) bool {
454 // Build a zero value of the flag's Value type, and see if the
455 // result of calling its String method equals the value passed in.
456 // This works unless the Value type is itself an interface type.
457 typ
:= reflect
.TypeOf(flag
.Value
)
459 if typ
.Kind() == reflect
.Pointer
{
460 z
= reflect
.New(typ
.Elem())
462 z
= reflect
.Zero(typ
)
464 return value
== z
.Interface().(Value
).String()
467 // UnquoteUsage extracts a back-quoted name from the usage
468 // string for a flag and returns it and the un-quoted usage.
469 // Given "a `name` to show" it returns ("name", "a name to show").
470 // If there are no back quotes, the name is an educated guess of the
471 // type of the flag's value, or the empty string if the flag is boolean.
472 func UnquoteUsage(flag
*Flag
) (name
string, usage
string) {
473 // Look for a back-quoted name, but avoid the strings package.
475 for i
:= 0; i
< len(usage
); i
++ {
477 for j
:= i
+ 1; j
< len(usage
); j
++ {
479 name
= usage
[i
+1 : j
]
480 usage
= usage
[:i
] + name
+ usage
[j
+1:]
484 break // Only one back quote; use type name.
487 // No explicit name, so use type if we can find one.
489 switch flag
.Value
.(type) {
496 case *intValue
, *int64Value
:
500 case *uintValue
, *uint64Value
:
506 // PrintDefaults prints, to standard error unless configured otherwise, the
507 // default values of all defined command-line flags in the set. See the
508 // documentation for the global function PrintDefaults for more information.
509 func (f
*FlagSet
) PrintDefaults() {
510 f
.VisitAll(func(flag
*Flag
) {
511 var b strings
.Builder
512 fmt
.Fprintf(&b
, " -%s", flag
.Name
) // Two spaces before -; see next two comments.
513 name
, usage
:= UnquoteUsage(flag
)
518 // Boolean flags of one ASCII letter are so common we
519 // treat them specially, putting their usage on the same line.
520 if b
.Len() <= 4 { // space, space, '-', 'x'.
523 // Four spaces before the tab triggers good alignment
524 // for both 4- and 8-space tab stops.
525 b
.WriteString("\n \t")
527 b
.WriteString(strings
.ReplaceAll(usage
, "\n", "\n \t"))
529 if !isZeroValue(flag
, flag
.DefValue
) {
530 if _
, ok
:= flag
.Value
.(*stringValue
); ok
{
531 // put quotes on the value
532 fmt
.Fprintf(&b
, " (default %q)", flag
.DefValue
)
534 fmt
.Fprintf(&b
, " (default %v)", flag
.DefValue
)
537 fmt
.Fprint(f
.Output(), b
.String(), "\n")
541 // PrintDefaults prints, to standard error unless configured otherwise,
542 // a usage message showing the default settings of all defined
543 // command-line flags.
544 // For an integer valued flag x, the default output has the form
546 // usage-message-for-x (default 7)
547 // The usage message will appear on a separate line for anything but
548 // a bool flag with a one-byte name. For bool flags, the type is
549 // omitted and if the flag name is one byte the usage message appears
550 // on the same line. The parenthetical default is omitted if the
551 // default is the zero value for the type. The listed type, here int,
552 // can be changed by placing a back-quoted name in the flag's usage
553 // string; the first such item in the message is taken to be a parameter
554 // name to show in the message and the back quotes are stripped from
555 // the message when displayed. For instance, given
556 // flag.String("I", "", "search `directory` for include files")
557 // the output will be
559 // search directory for include files.
561 // To change the destination for flag messages, call CommandLine.SetOutput.
562 func PrintDefaults() {
563 CommandLine
.PrintDefaults()
566 // defaultUsage is the default function to print a usage message.
567 func (f
*FlagSet
) defaultUsage() {
569 fmt
.Fprintf(f
.Output(), "Usage:\n")
571 fmt
.Fprintf(f
.Output(), "Usage of %s:\n", f
.name
)
576 // NOTE: Usage is not just defaultUsage(CommandLine)
577 // because it serves (via godoc flag Usage) as the example
578 // for how to write your own usage function.
580 // Usage prints a usage message documenting all defined command-line flags
581 // to CommandLine's output, which by default is os.Stderr.
582 // It is called when an error occurs while parsing flags.
583 // The function is a variable that may be changed to point to a custom function.
584 // By default it prints a simple header and calls PrintDefaults; for details about the
585 // format of the output and how to control it, see the documentation for PrintDefaults.
586 // Custom usage functions may choose to exit the program; by default exiting
587 // happens anyway as the command line's error handling strategy is set to
590 fmt
.Fprintf(CommandLine
.Output(), "Usage of %s:\n", os
.Args
[0])
594 // NFlag returns the number of flags that have been set.
595 func (f
*FlagSet
) NFlag() int { return len(f
.actual
) }
597 // NFlag returns the number of command-line flags that have been set.
598 func NFlag() int { return len(CommandLine
.actual
) }
600 // Arg returns the i'th argument. Arg(0) is the first remaining argument
601 // after flags have been processed. Arg returns an empty string if the
602 // requested element does not exist.
603 func (f
*FlagSet
) Arg(i
int) string {
604 if i
< 0 || i
>= len(f
.args
) {
610 // Arg returns the i'th command-line argument. Arg(0) is the first remaining argument
611 // after flags have been processed. Arg returns an empty string if the
612 // requested element does not exist.
613 func Arg(i
int) string {
614 return CommandLine
.Arg(i
)
617 // NArg is the number of arguments remaining after flags have been processed.
618 func (f
*FlagSet
) NArg() int { return len(f
.args
) }
620 // NArg is the number of arguments remaining after flags have been processed.
621 func NArg() int { return len(CommandLine
.args
) }
623 // Args returns the non-flag arguments.
624 func (f
*FlagSet
) Args() []string { return f
.args
}
626 // Args returns the non-flag command-line arguments.
627 func Args() []string { return CommandLine
.args
}
629 // BoolVar defines a bool flag with specified name, default value, and usage string.
630 // The argument p points to a bool variable in which to store the value of the flag.
631 func (f
*FlagSet
) BoolVar(p
*bool, name
string, value
bool, usage
string) {
632 f
.Var(newBoolValue(value
, p
), name
, usage
)
635 // BoolVar defines a bool flag with specified name, default value, and usage string.
636 // The argument p points to a bool variable in which to store the value of the flag.
637 func BoolVar(p
*bool, name
string, value
bool, usage
string) {
638 CommandLine
.Var(newBoolValue(value
, p
), name
, usage
)
641 // Bool defines a bool flag with specified name, default value, and usage string.
642 // The return value is the address of a bool variable that stores the value of the flag.
643 func (f
*FlagSet
) Bool(name
string, value
bool, usage
string) *bool {
645 f
.BoolVar(p
, name
, value
, usage
)
649 // Bool defines a bool flag with specified name, default value, and usage string.
650 // The return value is the address of a bool variable that stores the value of the flag.
651 func Bool(name
string, value
bool, usage
string) *bool {
652 return CommandLine
.Bool(name
, value
, usage
)
655 // IntVar defines an int flag with specified name, default value, and usage string.
656 // The argument p points to an int variable in which to store the value of the flag.
657 func (f
*FlagSet
) IntVar(p
*int, name
string, value
int, usage
string) {
658 f
.Var(newIntValue(value
, p
), name
, usage
)
661 // IntVar defines an int flag with specified name, default value, and usage string.
662 // The argument p points to an int variable in which to store the value of the flag.
663 func IntVar(p
*int, name
string, value
int, usage
string) {
664 CommandLine
.Var(newIntValue(value
, p
), name
, usage
)
667 // Int defines an int flag with specified name, default value, and usage string.
668 // The return value is the address of an int variable that stores the value of the flag.
669 func (f
*FlagSet
) Int(name
string, value
int, usage
string) *int {
671 f
.IntVar(p
, name
, value
, usage
)
675 // Int defines an int flag with specified name, default value, and usage string.
676 // The return value is the address of an int variable that stores the value of the flag.
677 func Int(name
string, value
int, usage
string) *int {
678 return CommandLine
.Int(name
, value
, usage
)
681 // Int64Var defines an int64 flag with specified name, default value, and usage string.
682 // The argument p points to an int64 variable in which to store the value of the flag.
683 func (f
*FlagSet
) Int64Var(p
*int64, name
string, value
int64, usage
string) {
684 f
.Var(newInt64Value(value
, p
), name
, usage
)
687 // Int64Var defines an int64 flag with specified name, default value, and usage string.
688 // The argument p points to an int64 variable in which to store the value of the flag.
689 func Int64Var(p
*int64, name
string, value
int64, usage
string) {
690 CommandLine
.Var(newInt64Value(value
, p
), name
, usage
)
693 // Int64 defines an int64 flag with specified name, default value, and usage string.
694 // The return value is the address of an int64 variable that stores the value of the flag.
695 func (f
*FlagSet
) Int64(name
string, value
int64, usage
string) *int64 {
697 f
.Int64Var(p
, name
, value
, usage
)
701 // Int64 defines an int64 flag with specified name, default value, and usage string.
702 // The return value is the address of an int64 variable that stores the value of the flag.
703 func Int64(name
string, value
int64, usage
string) *int64 {
704 return CommandLine
.Int64(name
, value
, usage
)
707 // UintVar defines a uint flag with specified name, default value, and usage string.
708 // The argument p points to a uint variable in which to store the value of the flag.
709 func (f
*FlagSet
) UintVar(p
*uint, name
string, value
uint, usage
string) {
710 f
.Var(newUintValue(value
, p
), name
, usage
)
713 // UintVar defines a uint flag with specified name, default value, and usage string.
714 // The argument p points to a uint variable in which to store the value of the flag.
715 func UintVar(p
*uint, name
string, value
uint, usage
string) {
716 CommandLine
.Var(newUintValue(value
, p
), name
, usage
)
719 // Uint defines a uint flag with specified name, default value, and usage string.
720 // The return value is the address of a uint variable that stores the value of the flag.
721 func (f
*FlagSet
) Uint(name
string, value
uint, usage
string) *uint {
723 f
.UintVar(p
, name
, value
, usage
)
727 // Uint defines a uint flag with specified name, default value, and usage string.
728 // The return value is the address of a uint variable that stores the value of the flag.
729 func Uint(name
string, value
uint, usage
string) *uint {
730 return CommandLine
.Uint(name
, value
, usage
)
733 // Uint64Var defines a uint64 flag with specified name, default value, and usage string.
734 // The argument p points to a uint64 variable in which to store the value of the flag.
735 func (f
*FlagSet
) Uint64Var(p
*uint64, name
string, value
uint64, usage
string) {
736 f
.Var(newUint64Value(value
, p
), name
, usage
)
739 // Uint64Var defines a uint64 flag with specified name, default value, and usage string.
740 // The argument p points to a uint64 variable in which to store the value of the flag.
741 func Uint64Var(p
*uint64, name
string, value
uint64, usage
string) {
742 CommandLine
.Var(newUint64Value(value
, p
), name
, usage
)
745 // Uint64 defines a uint64 flag with specified name, default value, and usage string.
746 // The return value is the address of a uint64 variable that stores the value of the flag.
747 func (f
*FlagSet
) Uint64(name
string, value
uint64, usage
string) *uint64 {
749 f
.Uint64Var(p
, name
, value
, usage
)
753 // Uint64 defines a uint64 flag with specified name, default value, and usage string.
754 // The return value is the address of a uint64 variable that stores the value of the flag.
755 func Uint64(name
string, value
uint64, usage
string) *uint64 {
756 return CommandLine
.Uint64(name
, value
, usage
)
759 // StringVar defines a string flag with specified name, default value, and usage string.
760 // The argument p points to a string variable in which to store the value of the flag.
761 func (f
*FlagSet
) StringVar(p
*string, name
string, value
string, usage
string) {
762 f
.Var(newStringValue(value
, p
), name
, usage
)
765 // StringVar defines a string flag with specified name, default value, and usage string.
766 // The argument p points to a string variable in which to store the value of the flag.
767 func StringVar(p
*string, name
string, value
string, usage
string) {
768 CommandLine
.Var(newStringValue(value
, p
), name
, usage
)
771 // String defines a string flag with specified name, default value, and usage string.
772 // The return value is the address of a string variable that stores the value of the flag.
773 func (f
*FlagSet
) String(name
string, value
string, usage
string) *string {
775 f
.StringVar(p
, name
, value
, usage
)
779 // String defines a string flag with specified name, default value, and usage string.
780 // The return value is the address of a string variable that stores the value of the flag.
781 func String(name
string, value
string, usage
string) *string {
782 return CommandLine
.String(name
, value
, usage
)
785 // Float64Var defines a float64 flag with specified name, default value, and usage string.
786 // The argument p points to a float64 variable in which to store the value of the flag.
787 func (f
*FlagSet
) Float64Var(p
*float64, name
string, value
float64, usage
string) {
788 f
.Var(newFloat64Value(value
, p
), name
, usage
)
791 // Float64Var defines a float64 flag with specified name, default value, and usage string.
792 // The argument p points to a float64 variable in which to store the value of the flag.
793 func Float64Var(p
*float64, name
string, value
float64, usage
string) {
794 CommandLine
.Var(newFloat64Value(value
, p
), name
, usage
)
797 // Float64 defines a float64 flag with specified name, default value, and usage string.
798 // The return value is the address of a float64 variable that stores the value of the flag.
799 func (f
*FlagSet
) Float64(name
string, value
float64, usage
string) *float64 {
801 f
.Float64Var(p
, name
, value
, usage
)
805 // Float64 defines a float64 flag with specified name, default value, and usage string.
806 // The return value is the address of a float64 variable that stores the value of the flag.
807 func Float64(name
string, value
float64, usage
string) *float64 {
808 return CommandLine
.Float64(name
, value
, usage
)
811 // DurationVar defines a time.Duration flag with specified name, default value, and usage string.
812 // The argument p points to a time.Duration variable in which to store the value of the flag.
813 // The flag accepts a value acceptable to time.ParseDuration.
814 func (f
*FlagSet
) DurationVar(p
*time
.Duration
, name
string, value time
.Duration
, usage
string) {
815 f
.Var(newDurationValue(value
, p
), name
, usage
)
818 // DurationVar defines a time.Duration flag with specified name, default value, and usage string.
819 // The argument p points to a time.Duration variable in which to store the value of the flag.
820 // The flag accepts a value acceptable to time.ParseDuration.
821 func DurationVar(p
*time
.Duration
, name
string, value time
.Duration
, usage
string) {
822 CommandLine
.Var(newDurationValue(value
, p
), name
, usage
)
825 // Duration defines a time.Duration flag with specified name, default value, and usage string.
826 // The return value is the address of a time.Duration variable that stores the value of the flag.
827 // The flag accepts a value acceptable to time.ParseDuration.
828 func (f
*FlagSet
) Duration(name
string, value time
.Duration
, usage
string) *time
.Duration
{
829 p
:= new(time
.Duration
)
830 f
.DurationVar(p
, name
, value
, usage
)
834 // Duration defines a time.Duration flag with specified name, default value, and usage string.
835 // The return value is the address of a time.Duration variable that stores the value of the flag.
836 // The flag accepts a value acceptable to time.ParseDuration.
837 func Duration(name
string, value time
.Duration
, usage
string) *time
.Duration
{
838 return CommandLine
.Duration(name
, value
, usage
)
841 // Func defines a flag with the specified name and usage string.
842 // Each time the flag is seen, fn is called with the value of the flag.
843 // If fn returns a non-nil error, it will be treated as a flag value parsing error.
844 func (f
*FlagSet
) Func(name
, usage
string, fn
func(string) error
) {
845 f
.Var(funcValue(fn
), name
, usage
)
848 // Func defines a flag with the specified name and usage string.
849 // Each time the flag is seen, fn is called with the value of the flag.
850 // If fn returns a non-nil error, it will be treated as a flag value parsing error.
851 func Func(name
, usage
string, fn
func(string) error
) {
852 CommandLine
.Func(name
, usage
, fn
)
855 // Var defines a flag with the specified name and usage string. The type and
856 // value of the flag are represented by the first argument, of type Value, which
857 // typically holds a user-defined implementation of Value. For instance, the
858 // caller could create a flag that turns a comma-separated string into a slice
859 // of strings by giving the slice the methods of Value; in particular, Set would
860 // decompose the comma-separated string into the slice.
861 func (f
*FlagSet
) Var(value Value
, name
string, usage
string) {
862 // Flag must not begin "-" or contain "=".
863 if strings
.HasPrefix(name
, "-") {
864 panic(f
.sprintf("flag %q begins with -", name
))
865 } else if strings
.Contains(name
, "=") {
866 panic(f
.sprintf("flag %q contains =", name
))
869 // Remember the default value as a string; it won't change.
870 flag
:= &Flag
{name
, usage
, value
, value
.String()}
871 _
, alreadythere
:= f
.formal
[name
]
875 msg
= f
.sprintf("flag redefined: %s", name
)
877 msg
= f
.sprintf("%s flag redefined: %s", f
.name
, name
)
879 panic(msg
) // Happens only if flags are declared with identical names
882 f
.formal
= make(map[string]*Flag
)
884 f
.formal
[name
] = flag
887 // Var defines a flag with the specified name and usage string. The type and
888 // value of the flag are represented by the first argument, of type Value, which
889 // typically holds a user-defined implementation of Value. For instance, the
890 // caller could create a flag that turns a comma-separated string into a slice
891 // of strings by giving the slice the methods of Value; in particular, Set would
892 // decompose the comma-separated string into the slice.
893 func Var(value Value
, name
string, usage
string) {
894 CommandLine
.Var(value
, name
, usage
)
897 // sprintf formats the message, prints it to output, and returns it.
898 func (f
*FlagSet
) sprintf(format
string, a
...any
) string {
899 msg
:= fmt
.Sprintf(format
, a
...)
900 fmt
.Fprintln(f
.Output(), msg
)
904 // failf prints to standard error a formatted error and usage message and
905 // returns the error.
906 func (f
*FlagSet
) failf(format
string, a
...any
) error
{
907 msg
:= f
.sprintf(format
, a
...)
909 return errors
.New(msg
)
912 // usage calls the Usage method for the flag set if one is specified,
913 // or the appropriate default usage function otherwise.
914 func (f
*FlagSet
) usage() {
922 // parseOne parses one flag. It reports whether a flag was seen.
923 func (f
*FlagSet
) parseOne() (bool, error
) {
924 if len(f
.args
) == 0 {
928 if len(s
) < 2 || s
[0] != '-' {
934 if len(s
) == 2 { // "--" terminates the flags
939 name
:= s
[numMinuses
:]
940 if len(name
) == 0 || name
[0] == '-' || name
[0] == '=' {
941 return false, f
.failf("bad flag syntax: %s", s
)
944 // it's a flag. does it have an argument?
948 for i
:= 1; i
< len(name
); i
++ { // equals cannot be first
957 flag
, alreadythere
:= m
[name
] // BUG
959 if name
== "help" || name
== "h" { // special case for nice help message.
961 return false, ErrHelp
963 return false, f
.failf("flag provided but not defined: -%s", name
)
966 if fv
, ok
:= flag
.Value
.(boolFlag
); ok
&& fv
.IsBoolFlag() { // special case: doesn't need an arg
968 if err
:= fv
.Set(value
); err
!= nil {
969 return false, f
.failf("invalid boolean value %q for -%s: %v", value
, name
, err
)
972 if err
:= fv
.Set("true"); err
!= nil {
973 return false, f
.failf("invalid boolean flag %s: %v", name
, err
)
977 // It must have a value, which might be the next argument.
978 if !hasValue
&& len(f
.args
) > 0 {
979 // value is the next arg
981 value
, f
.args
= f
.args
[0], f
.args
[1:]
984 return false, f
.failf("flag needs an argument: -%s", name
)
986 if err
:= flag
.Value
.Set(value
); err
!= nil {
987 return false, f
.failf("invalid value %q for flag -%s: %v", value
, name
, err
)
991 f
.actual
= make(map[string]*Flag
)
993 f
.actual
[name
] = flag
997 // Parse parses flag definitions from the argument list, which should not
998 // include the command name. Must be called after all flags in the FlagSet
999 // are defined and before flags are accessed by the program.
1000 // The return value will be ErrHelp if -help or -h were set but not defined.
1001 func (f
*FlagSet
) Parse(arguments
[]string) error
{
1005 seen
, err
:= f
.parseOne()
1012 switch f
.errorHandling
{
1013 case ContinueOnError
:
1027 // Parsed reports whether f.Parse has been called.
1028 func (f
*FlagSet
) Parsed() bool {
1032 // Parse parses the command-line flags from os.Args[1:]. Must be called
1033 // after all flags are defined and before flags are accessed by the program.
1035 // Ignore errors; CommandLine is set for ExitOnError.
1036 CommandLine
.Parse(os
.Args
[1:])
1039 // Parsed reports whether the command-line flags have been parsed.
1040 func Parsed() bool {
1041 return CommandLine
.Parsed()
1044 // CommandLine is the default set of command-line flags, parsed from os.Args.
1045 // The top-level functions such as BoolVar, Arg, and so on are wrappers for the
1046 // methods of CommandLine.
1047 var CommandLine
= NewFlagSet(os
.Args
[0], ExitOnError
)
1050 // Override generic FlagSet default Usage with call to global Usage.
1051 // Note: This is not CommandLine.Usage = Usage,
1052 // because we want any eventual call to use any updated value of Usage,
1053 // not the value it has when this line is run.
1054 CommandLine
.Usage
= commandLineUsage
1057 func commandLineUsage() {
1061 // NewFlagSet returns a new, empty flag set with the specified name and
1062 // error handling property. If the name is not empty, it will be printed
1063 // in the default usage message and in error messages.
1064 func NewFlagSet(name
string, errorHandling ErrorHandling
) *FlagSet
{
1067 errorHandling
: errorHandling
,
1069 f
.Usage
= f
.defaultUsage
1073 // Init sets the name and error handling property for a flag set.
1074 // By default, the zero FlagSet uses an empty name and the
1075 // ContinueOnError error handling policy.
1076 func (f
*FlagSet
) Init(name
string, errorHandling ErrorHandling
) {
1078 f
.errorHandling
= errorHandling