Namespace: go.std.flag




Provides a low-level interface to the flag package.

Package flag implements command-line flag parsing.


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
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 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.




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.


Functions, Macros, and Special Forms