Namespace: go.std.flag

v1.0

Contents

• Summary
• Index
• Constants
• Variables
• Functions, Macros, and Special Forms
• Types

Summary

Provides a low-level interface to the flag package.

Package flag implements command-line flag parsing.

Usage

Define flags using flag.String(), Bool(), Int(), etc.

This declares an integer flag, -n, stored in the pointer nFlag, with type *int:
import "flag"
var nFlag = flag.Int("n", 1234, "help message for flag n")
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 following the flags are available as the
slice flag.Args() or individually as flag.Arg(i).
The arguments are indexed from 0 through flag.NArg()-1.

Command line flag syntax

The following forms are permitted:

-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 *
where * is a Unix shell wildcard, 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, T, F, true, false, TRUE, FALSE, True, False
Duration flags accept any input valid for time.ParseDuration.

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.

Index

• *ErrorHandling
• *Flag
• *FlagSet
• Arg
• Args
• Bool
• CommandLine
• ContinueOnError
• Duration
• DurationVar
• ErrHelp
• ErrorHandling
• ExitOnError
• Flag
• FlagSet
• Float64
• Getter
• Int
• Int64
• Lookup
• NArg
• NFlag
• NewFlagSet
• PanicOnError
• Parse
• Parsed
• PrintDefaults
• Set
• String
• Uint
• Uint64
• UnquoteUsage
• Usage
• Value
• Var
• arrayOfErrorHandling
• arrayOfFlag
• arrayOfFlagSet
• arrayOfGetter
• arrayOfValue

Legend

Constant Variable Function Macro Special form Type GoVar Receiver/Method

Constants

Constants are variables with :const true in their metadata. Joker currently does not recognize them as special; as such, it allows redefining them or their values.

(None.)

Variables

• CommandLine

  Var v1.0

  CommandLine is the default set of command-line flags, parsed from os.Args.
  The top-level functions such as BoolVar, Arg, and so on are wrappers for the
  methods of CommandLine.
  

• ContinueOnError

  GoObject v1.0

  Return a descriptive error.
  

• ErrHelp

  Var v1.0

  ErrHelp is the error returned if the -help or -h flag is invoked
  but no such flag is defined.
  

• ExitOnError

  GoObject v1.0

  Call os.Exit(2) or for -h/-help Exit(0).
  

• PanicOnError

  GoObject v1.0

  Call panic with a descriptive error.
  

• Usage

  Var v1.0

  Usage prints a usage message documenting all defined command-line flags
  to CommandLine's output, which by default is os.Stderr.
  It is called when an error occurs while parsing flags.
  The function is a variable that may be changed to point to a custom function.
  By default it prints a simple header and calls PrintDefaults; for details about the
  format of the output and how to control it, see the documentation for PrintDefaults.
  Custom usage functions may choose to exit the program; by default exiting
  happens anyway as the command line's error handling strategy is set to
  ExitOnError.
  

Functions, Macros, and Special Forms

• Arg

  Function v1.0

  (Arg i)
  

  Arg returns the i'th command-line argument. Arg(0) is the first remaining argument
  after flags have been processed. Arg returns an empty string if the
  requested element does not exist.
  
  Go input arguments: (i int)
  
  Go returns: string
  
  Joker input arguments: [^Int i]
  
  Joker returns: ^String

• Args

  Function v1.0

  (Args)
  

  Args returns the non-flag command-line arguments.
  
  Go returns: []string
  
  Joker input arguments: []
  
  Joker returns: ^arrayOfString

• Bool

  Function v1.0

  (Bool name value usage)
  

  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.
  
  Go input arguments: (name string, value bool, usage string)
  
  Go returns: *bool
  
  Joker input arguments: [^String name, ^Boolean value, ^String usage]
  
  Joker returns: ^*Boolean

• Duration

  Function v1.0

  (Duration name value usage)
  

  Duration defines a time.Duration flag with specified name, default value, and usage string.
  The return value is the address of a time.Duration variable that stores the value of the flag.
  The flag accepts a value acceptable to time.ParseDuration.
  
  Go input arguments: (name string, value time.Duration, usage string)
  
  Go returns: *time.Duration
  
  Joker input arguments: [^String name, ^go.std.time/Duration value, ^String usage]
  
  Joker returns: ^go.std.time/*Duration

• DurationVar

  Function v1.0

  (DurationVar p name value usage)
  

  DurationVar defines a time.Duration flag with specified name, default value, and usage string.
  The argument p points to a time.Duration variable in which to store the value of the flag.
  The flag accepts a value acceptable to time.ParseDuration.
  
  Go input arguments: (p *time.Duration, name string, value time.Duration, usage string)
  
  Joker input arguments: [^go.std.time/*Duration p, ^String name, ^go.std.time/Duration value, ^String usage]

• Float64

  Function v1.0

  (Float64 name value usage)
  

  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.
  
  Go input arguments: (name string, value float64, usage string)
  
  Go returns: *float64
  
  Joker input arguments: [^String name, ^Double value, ^String usage]
  
  Joker returns: ^*Double

• Int

  Function v1.0

  (Int name value usage)
  

  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.
  
  Go input arguments: (name string, value int, usage string)
  
  Go returns: *int
  
  Joker input arguments: [^String name, ^Int value, ^String usage]
  
  Joker returns: ^*Int

• Int64

  Function v1.0

  (Int64 name value usage)
  

  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.
  
  Go input arguments: (name string, value int64, usage string)
  
  Go returns: *int64
  
  Joker input arguments: [^String name, ^BigInt value, ^String usage]
  
  Joker returns: ^*BigInt

• Lookup

  Function v1.0

  (Lookup name)
  

  Lookup returns the Flag structure of the named command-line flag,
  returning nil if none exists.
  
  Go input arguments: (name string)
  
  Go returns: *Flag
  
  Joker input arguments: [^String name]
  
  Joker returns: ^*Flag

• NArg

  Function v1.0

  (NArg)
  

  NArg is the number of arguments remaining after flags have been processed.
  
  Go returns: int
  
  Joker input arguments: []
  
  Joker returns: ^Int

• NFlag

  Function v1.0

  (NFlag)
  

  NFlag returns the number of command-line flags that have been set.
  
  Go returns: int
  
  Joker input arguments: []
  
  Joker returns: ^Int

• NewFlagSet

  Function v1.0

  (NewFlagSet name errorHandling)
  

  NewFlagSet returns a new, empty flag set with the specified name and
  error handling property. If the name is not empty, it will be printed
  in the default usage message and in error messages.
  
  Go input arguments: (name string, errorHandling ErrorHandling)
  
  Go returns: *FlagSet
  
  Joker input arguments: [^String name, ^ErrorHandling errorHandling]
  
  Joker returns: ^*FlagSet

• Parse

  Function v1.0

  (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.
  
  Joker input arguments: []

• Parsed

  Function v1.0

  (Parsed)
  

  Parsed reports whether the command-line flags have been parsed.
  
  Go returns: bool
  
  Joker input arguments: []
  
  Joker returns: ^Boolean

• PrintDefaults

  Function v1.0

  (PrintDefaults)
  

  PrintDefaults prints, to standard error unless configured otherwise,
  a usage message showing the default settings of all defined
  command-line flags.
  For an integer valued flag x, the default output has the form
  -x int
  usage-message-for-x (default 7)
  The usage message will appear on a separate line for anything but
  a bool flag with a one-byte name. For bool flags, the type is
  omitted and if the flag name is one byte the usage message appears
  on the same line. The parenthetical default is omitted if the
  default is the zero value for the type. The listed type, here int,
  can be changed by placing a back-quoted name in the flag's usage
  string; the first such item in the message is taken to be a parameter
  name to show in the message and the back quotes are stripped from
  the message when displayed. For instance, given
  flag.String("I", "", "search `directory` for include files")
  the output will be
  -I directory
  search directory for include files.
  
  To change the destination for flag messages, call CommandLine.SetOutput.
  
  Joker input arguments: []

• Set

  Function v1.0

  (Set name value)
  

  Set sets the value of the named command-line flag.
  
  Go input arguments: (name string, value string)
  
  Go returns: error
  
  Joker input arguments: [^String name, ^String value]
  
  Joker returns: ^Error

• String

  Function v1.0

  (String name value usage)
  

  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.
  
  Go input arguments: (name string, value string, usage string)
  
  Go returns: *string
  
  Joker input arguments: [^String name, ^String value, ^String usage]
  
  Joker returns: ^*String

• Uint

  Function v1.0

  (Uint name value usage)
  

  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.
  
  Go input arguments: (name string, value uint, usage string)
  
  Go returns: *uint
  
  Joker input arguments: [^String name, ^Number value, ^String usage]
  
  Joker returns: ^*Number

• Uint64

  Function v1.0

  (Uint64 name value usage)
  

  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.
  
  Go input arguments: (name string, value uint64, usage string)
  
  Go returns: *uint64
  
  Joker input arguments: [^String name, ^Number value, ^String usage]
  
  Joker returns: ^*Number

• UnquoteUsage

  Function v1.0

  (UnquoteUsage flag)
  

  UnquoteUsage extracts a back-quoted name from the usage
  string for a flag and returns it and the un-quoted usage.
  Given "a `name` to show" it returns ("name", "a name to show").
  If there are no back quotes, the name is an educated guess of the
  type of the flag's value, or the empty string if the flag is boolean.
  
  Go input arguments: (flag *Flag)
  
  Go returns: (name string, usage string)
  
  Joker input arguments: [^*Flag flag]
  
  Joker returns: [^String name, ^String usage]

• Var

  Function v1.0

  (Var value name usage)
  

  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.
  
  Go input arguments: (value Value, name string, usage string)
  
  Joker input arguments: [^Value value, ^String name, ^String usage]

Types

• *ErrorHandling

  Concrete Type v1.0

  ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
  

• *Flag

  Concrete Type v1.0

  A Flag represents the state of a flag.
  

• *FlagSet

  Concrete Type v1.0

  A FlagSet represents a set of defined flags. The zero value of a FlagSet
  has no name and has ContinueOnError error handling.
  
  Flag names must be unique within a FlagSet. An attempt to define a flag whose
  name is already in use will cause a panic.
  

• Arg

  Receiver for *FlagSet v1.0

  ([i])
  

  Arg returns the i'th argument. Arg(0) is the first remaining argument
  after flags have been processed. Arg returns an empty string if the
  requested element does not exist.
  

• Args

  Receiver for *FlagSet v1.0

  ([])
  

  Args returns the non-flag arguments.
  

• Bool

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Duration

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  Duration defines a time.Duration flag with specified name, default value, and usage string.
  The return value is the address of a time.Duration variable that stores the value of the flag.
  The flag accepts a value acceptable to time.ParseDuration.
  

• DurationVar

  Receiver for *FlagSet v1.0

  ([p name value usage])
  

  DurationVar defines a time.Duration flag with specified name, default value, and usage string.
  The argument p points to a time.Duration variable in which to store the value of the flag.
  The flag accepts a value acceptable to time.ParseDuration.
  

• ErrorHandling

  Receiver for *FlagSet v1.0

  ([])
  

  ErrorHandling returns the error handling behavior of the flag set.
  

• Float64

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Init

  Receiver for *FlagSet v1.0

  ([name errorHandling])
  

  Init sets the name and error handling property for a flag set.
  By default, the zero FlagSet uses an empty name and the
  ContinueOnError error handling policy.
  

• Int

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Int64

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Lookup

  Receiver for *FlagSet v1.0

  ([name])
  

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

• NArg

  Receiver for *FlagSet v1.0

  ([])
  

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

• NFlag

  Receiver for *FlagSet v1.0

  ([])
  

  NFlag returns the number of flags that have been set.
  

• Name

  Receiver for *FlagSet v1.0

  ([])
  

  Name returns the name of the flag set.
  

• Output

  Receiver for *FlagSet v1.0

  ([])
  

  Output returns the destination for usage and error messages. os.Stderr is returned if
  output was not set or was set to nil.
  

• Parse

  Receiver for *FlagSet v1.0

  ([arguments])
  

  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 or -h were set but not defined.
  

• Parsed

  Receiver for *FlagSet v1.0

  ([])
  

  Parsed reports whether f.Parse has been called.
  

• PrintDefaults

  Receiver for *FlagSet v1.0

  ([])
  

  PrintDefaults prints, to standard error unless configured otherwise, the
  default values of all defined command-line flags in the set. See the
  documentation for the global function PrintDefaults for more information.
  

• Set

  Receiver for *FlagSet v1.0

  ([name value])
  

  Set sets the value of the named flag.
  

• SetOutput

  Receiver for *FlagSet v1.0

  ([output])
  

  SetOutput sets the destination for usage and error messages.
  If output is nil, os.Stderr is used.
  

• String

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Uint

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Uint64

  Receiver for *FlagSet v1.0

  ([name value usage])
  

  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.
  

• Var

  Receiver for *FlagSet v1.0

  ([value name usage])
  

  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.
  

• ErrorHandling

  Concrete Type v1.0

  ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
  

• Flag

  Concrete Type v1.0

  A Flag represents the state of a flag.
  

• FlagSet

  Concrete Type v1.0

  A FlagSet represents a set of defined flags. The zero value of a FlagSet
  has no name and has ContinueOnError error handling.
  
  Flag names must be unique within a FlagSet. An attempt to define a flag whose
  name is already in use will cause a panic.
  

• Getter

  Abstract Type v1.0

  Getter is an interface that allows the contents of a Value to be retrieved.
  It wraps the Value interface, rather than being part of it, because it
  appeared after Go 1 and its compatibility rules. All Value types provided
  by this package satisfy the Getter interface, except the type used by Func.
  

• Get

  Method for Getter v1.0

  ([])
  

• Set

  Method for Getter v1.0

  ([arg1])
  

• String

  Method for Getter v1.0

  ([])
  

• Value

  Abstract Type v1.0

  Value is the interface to the dynamic value stored in a flag.
  (The default value is represented as a string.)
  
  If a Value has an IsBoolFlag() bool method returning true,
  the command-line parser makes -name equivalent to -name=true
  rather than using the next command-line argument.
  
  Set is called once, in command line order, for each flag present.
  The flag package may call the String method with a zero-valued receiver,
  such as a nil pointer.
  

• Set

  Method for Value v1.0

  ([arg1])
  

• String

  Method for Value v1.0

  ([])
  

• arrayOfErrorHandling

  Concrete Type v1.0

  ErrorHandling defines how FlagSet.Parse behaves if the parse fails.
  

• arrayOfFlag

  Concrete Type v1.0

  A Flag represents the state of a flag.
  

• arrayOfFlagSet

  Concrete Type v1.0

  A FlagSet represents a set of defined flags. The zero value of a FlagSet
  has no name and has ContinueOnError error handling.
  
  Flag names must be unique within a FlagSet. An attempt to define a flag whose
  name is already in use will cause a panic.
  

• arrayOfGetter

  Concrete Type v1.0

  Getter is an interface that allows the contents of a Value to be retrieved.
  It wraps the Value interface, rather than being part of it, because it
  appeared after Go 1 and its compatibility rules. All Value types provided
  by this package satisfy the Getter interface, except the type used by Func.
  

• arrayOfValue

  Concrete Type v1.0

  Value is the interface to the dynamic value stored in a flag.
  (The default value is represented as a string.)
  
  If a Value has an IsBoolFlag() bool method returning true,
  the command-line parser makes -name equivalent to -name=true
  rather than using the next command-line argument.
  
  Set is called once, in command line order, for each flag present.
  The flag package may call the String method with a zero-valued receiver,
  such as a nil pointer.