Package flag
import "flag"
Package flag implements command-line flag parsing.
Usage:
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")
}
Or you can create custom flags that satisfy the Value interface (with pointer receivers) and couple them to flag parsing by
flag.Var(&flagVal, "name", "help message for flagname")
For such flags, the default value is just the initial value of the variable.
After all flags are defined, call
flag.Parse()
to parse the command line into the defined flags.
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);
After parsing, the arguments after the flag are available as the slice flag.Args() or individually as flag.Arg(i). The arguments 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.
The default set of command-line flags is controlled by top-level functions. The FlagSet type allows one to define independent sets of flags, such as to implement subcommands in a command-line interface. The methods of FlagSet are analogous to the top-level functions for the command-line flag set.
Package files
flag.goVariables
ErrHelp is the error returned if the flag -help is invoked but no such flag is defined.
var ErrHelp = os.NewError("flag: help requested")
Usage prints to standard error a usage message documenting all defined command-line flags. The function is a variable that may be changed to point to a custom function.
var Usage = func() {
defaultUsage(commandLine)
}
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 Float64
func Float64(name string, value float64, usage string) *float64
Float64 defines an int 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 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
NFlag returns the number of command-line flags that have been set.
func Parse
func Parse()
Parse parses the command-line flags from os.Args[1:]. Must be called after all flags are defined and before flags are accessed by the program.
func PrintDefaults
func PrintDefaults()
PrintDefaults prints to standard error the default values of all defined command-line flags.
func Set
func Set(name, value string) bool
Set sets the value of the named command-line flag. It returns true if the set succeeded; false if there is no such flag defined.
func String
func String(name string, 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 string, 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 Var
func Var(value Value, name string, usage string)
Var defines a flag with the specified name and usage string. The type and value of the flag are represented by the first argument, of type Value, which typically holds a user-defined implementation of Value. For instance, the caller could create a flag that turns a comma-separated string into a slice of strings by giving the slice the methods of Value; in particular, Set would decompose the comma-separated string into the slice.
func Visit
func Visit(fn func(*Flag))
Visit visits the command-line flags in lexicographical order, calling fn for each. It visits only those flags that have been set.
func VisitAll
func VisitAll(fn func(*Flag))
VisitAll visits the command-line flags in lexicographical order, calling fn for each. It visits all flags, even those not set.
type ErrorHandling
ErrorHandling defines how to handle flag parsing errors.
type ErrorHandling int
const (
ContinueOnError ErrorHandling = iota
ExitOnError
PanicOnError
)
type Flag
A Flag represents the state of a flag.
type Flag struct {
Name string // name as it appears on command line
Usage string // help message
Value Value // value as set
DefValue string // default value (as text); for usage message
}
func Lookup
func Lookup(name string) *Flag
Lookup returns the Flag structure of the named command-line flag, returning nil if none exists.
type FlagSet
A FlagSet represents a set of defined flags.
type FlagSet struct {
// Usage is the function called when an error occurs while parsing flags.
// The field is a function (not a method) that may be changed to point to
// a custom error handler.
Usage func()
// contains filtered or unexported fields
}
func NewFlagSet
func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet
NewFlagSet returns a new, empty flag set with the specified name and error handling property.
func (*FlagSet) Arg
func (f *FlagSet) Arg(i int) string
Arg returns the i'th argument. Arg(0) is the first remaining argument after flags have been processed.
func (*FlagSet) Args
func (f *FlagSet) Args() []string
Args returns the non-flag arguments.
func (*FlagSet) Bool
func (f *FlagSet) 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 (*FlagSet) BoolVar
func (f *FlagSet) 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 (*FlagSet) Float64
func (f *FlagSet) 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 (*FlagSet) Float64Var
func (f *FlagSet) 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 (*FlagSet) Int
func (f *FlagSet) 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 (*FlagSet) Int64
func (f *FlagSet) 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 (*FlagSet) Int64Var
func (f *FlagSet) 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 (*FlagSet) IntVar
func (f *FlagSet) 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 (*FlagSet) Lookup
func (f *FlagSet) Lookup(name string) *Flag
Lookup returns the Flag structure of the named flag, returning nil if none exists.
func (*FlagSet) NArg
func (f *FlagSet) NArg() int
NArg is the number of arguments remaining after flags have been processed.
func (*FlagSet) NFlag
func (f *FlagSet) NFlag() int
NFlag returns the number of flags that have been set.
func (*FlagSet) Parse
func (f *FlagSet) Parse(arguments []string) os.Error
Parse parses flag definitions from the argument list, which should not include the command name. Must be called after all flags in the FlagSet are defined and before flags are accessed by the program. The return value will be ErrHelp if -help was set but not defined.
func (*FlagSet) PrintDefaults
func (f *FlagSet) PrintDefaults()
PrintDefaults prints to standard error the default values of all defined flags in the set.
func (*FlagSet) Set
func (f *FlagSet) 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 (*FlagSet) String
func (f *FlagSet) String(name string, 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 (*FlagSet) StringVar
func (f *FlagSet) StringVar(p *string, name string, 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 (*FlagSet) Uint
func (f *FlagSet) 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 (*FlagSet) Uint64
func (f *FlagSet) 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 (*FlagSet) Uint64Var
func (f *FlagSet) 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 (*FlagSet) UintVar
func (f *FlagSet) 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 (*FlagSet) Var
func (f *FlagSet) Var(value Value, name string, usage string)
Var defines a flag with the specified name and usage string. The type and value of the flag are represented by the first argument, of type Value, which typically holds a user-defined implementation of Value. For instance, the caller could create a flag that turns a comma-separated string into a slice of strings by giving the slice the methods of Value; in particular, Set would decompose the comma-separated string into the slice.
func (*FlagSet) Visit
func (f *FlagSet) Visit(fn func(*Flag))
Visit visits the flags in lexicographical order, calling fn for each. It visits only those flags that have been set.
func (*FlagSet) VisitAll
func (f *FlagSet) VisitAll(fn func(*Flag))
VisitAll visits the flags in lexicographical order, calling fn for each. It visits all flags, even those not set.
type Value
Value is the interface to the dynamic value stored in a flag. (The default value is represented as a string.)
type Value interface {
String() string
Set(string) bool
}