Package flag implements command-line flag parsing.
Command-line flags are a common way to specify options for command-line programs. For example, in ls -l the -l is a command-line flag.
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
type Value
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.
type Value interface {
String() string
Set(string) error
}
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.