flag

Documentation

Overview

The flag package implements command-line flag parsing.

Usage:

1. Define flags using flag.String(), Bool(), Int(), etc. Example: import "flag" var ip *int = flag.Int("flagname", 1234, "help message for flagname")

If you like, you can bind the flag to a variable using the Var() functions.

var flagvar int
func init() {
	flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
}

2. After all flags are defined, call flag.Parse()

to parse the command line into the defined flags.

3) Flags may then be used directly. If you're using the flags themselves, they are all pointers; if you bind to variables, they're values.

fmt.Println("ip has value ", *ip);
fmt.Println("flagvar has value ", flagvar);

4) After parsing, flag.Arg(i) is the i'th argument after the flags. Args are indexed from 0 up to flag.NArg().

Command line flag syntax:

-flag
-flag=x
-flag x  // non-boolean flags only

One or two minus signs may be used; they are equivalent. The last form is not permitted for boolean flags because the meaning of the command

cmd -x *

will change if there is a file called 0, false, etc. You must use the -flag=false form to turn off a boolean flag.

Flag parsing stops just before the first non-flag argument ("-" is a non-flag argument) or after the terminator "--".

Integer flags accept 1234, 0664, 0x1234 and may be negative. Boolean flags may be 1, 0, t, f, true, false, TRUE, FALSE, True, False.

Index

• Variables
• func Arg(i int) string
• func Args() []string
• func Bool(name string, value bool, usage string) *bool
• func BoolVar(p *bool, name string, value bool, usage string)
• func Float(name string, value float, usage string) *float
• func Float64(name string, value float64, usage string) *float64
• func Float64Var(p *float64, name string, value float64, usage string)
• func FloatVar(p *float, name string, value float, usage string)
• func Int(name string, value int, usage string) *int
• func Int64(name string, value int64, usage string) *int64
• func Int64Var(p *int64, name string, value int64, usage string)
• func IntVar(p *int, name string, value int, usage string)
• func NArg() int
• func NFlag() int
• func Parse()
• func PrintDefaults()
• func Set(name, value string) bool
• func String(name, value string, usage string) *string
• func StringVar(p *string, name, value string, usage string)
• func Uint(name string, value uint, usage string) *uint
• func Uint64(name string, value uint64, usage string) *uint64
• func Uint64Var(p *uint64, name string, value uint64, usage string)
• func UintVar(p *uint, name string, value uint, usage string)
• func Visit(fn func(*Flag))
• func VisitAll(fn func(*Flag))
• type Flag
  • func Lookup(name string) *Flag
• type FlagValue

Variables

var Usage = func() {
	fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
	PrintDefaults()
}

Usage prints to standard error a default usage message documenting all defined flags. The function is a variable that may be changed to point to a custom function.

Functions

func Arg

func Arg(i int) string

Arg returns the i'th command-line argument. Arg(0) is the first remaining argument after flags have been processed.

func Args

func Args() []string

Args returns the non-flag command-line arguments.

func Bool

func Bool(name string, value bool, usage string) *bool

Bool defines a bool flag with specified name, default value, and usage string. The return value is the address of a bool variable that stores the value of the flag.

func BoolVar

func BoolVar(p *bool, name string, value bool, usage string)

BoolVar defines a bool flag with specified name, default value, and usage string. The argument p points to a bool variable in which to store the value of the flag.

func Float

func Float(name string, value float, usage string) *float

Float defines a float flag with specified name, default value, and usage string. The return value is the address of a float variable that stores the value of the flag.

func Float64

func Float64(name string, value float64, usage string) *float64

Float64 defines a float64 flag with specified name, default value, and usage string. The return value is the address of a float64 variable that stores the value of the flag.

func Float64Var

func Float64Var(p *float64, name string, value float64, usage string)

Float64Var defines a float64 flag with specified name, default value, and usage string. The argument p points to a float64 variable in which to store the value of the flag.

func FloatVar

func FloatVar(p *float, name string, value float, usage string)

FloatVar defines a float flag with specified name, default value, and usage string. The argument p points to a float variable in which to store the value of the flag.

func Int

func Int(name string, value int, usage string) *int

Int defines an int flag with specified name, default value, and usage string. The return value is the address of an int variable that stores the value of the flag.

func Int64

func Int64(name string, value int64, usage string) *int64

Int64 defines an int64 flag with specified name, default value, and usage string. The return value is the address of an int64 variable that stores the value of the flag.

func Int64Var

func Int64Var(p *int64, name string, value int64, usage string)

Int64Var defines an int64 flag with specified name, default value, and usage string. The argument p points to an int64 variable in which to store the value of the flag.

func IntVar

func IntVar(p *int, name string, value int, usage string)

IntVar defines an int flag with specified name, default value, and usage string. The argument p points to an int variable in which to store the value of the flag.

func NArg

func NArg() int

NArg is the number of arguments remaining after flags have been processed.

func NFlag

func NFlag() int

func Parse

func Parse()

Parse parses the command-line flags. Must be called after all flags are defined and before any are accessed by the program.

func PrintDefaults

func PrintDefaults()

PrintDefaults prints to standard error the default values of all defined flags.

func Set

func Set(name, value string) bool

Set sets the value of the named flag. It returns true if the set succeeded; false if there is no such flag defined.

func String

func String(name, value string, usage string) *string

String defines a string flag with specified name, default value, and usage string. The return value is the address of a string variable that stores the value of the flag.

func StringVar

func StringVar(p *string, name, value string, usage string)

StringVar defines a string flag with specified name, default value, and usage string. The argument p points to a string variable in which to store the value of the flag.

func Uint

func Uint(name string, value uint, usage string) *uint

Uint defines a uint flag with specified name, default value, and usage string. The return value is the address of a uint variable that stores the value of the flag.

func Uint64

func Uint64(name string, value uint64, usage string) *uint64

Uint64 defines a uint64 flag with specified name, default value, and usage string. The return value is the address of a uint64 variable that stores the value of the flag.

func Uint64Var

func Uint64Var(p *uint64, name string, value uint64, usage string)

Uint64Var defines a uint64 flag with specified name, default value, and usage string. The argument p points to a uint64 variable in which to store the value of the flag.

func UintVar

func UintVar(p *uint, name string, value uint, usage string)

UintVar defines a uint flag with specified name, default value, and usage string. The argument p points to a uint variable in which to store the value of the flag.

func Visit

func Visit(fn func(*Flag))

Visit visits the flags, calling fn for each. It visits only those flags that have been set.

func VisitAll

func VisitAll(fn func(*Flag))

VisitAll visits the flags, calling fn for each. It visits all flags, even those not set.

Types

type Flag

type Flag struct {
	Name     string    // name as it appears on command line
	Usage    string    // help message
	Value    FlagValue // value as set
	DefValue string    // default value (as text); for usage message
}

A Flag represents the state of a flag.

func Lookup

func Lookup(name string) *Flag

Lookup returns the Flag structure of the named flag, returning nil if none exists.

type FlagValue

type FlagValue interface {
	String() string
	// contains filtered or unexported methods
}

FlagValue is the interface to the dynamic value stored in a flag. (The default value is represented as a string.)