structarg

Argument parser for go that defines and parses command line arguements into a struct type variable. The attributes of arguments are defined in the comment tags of the struct. after parsing command-line argument or configuration files, the values are stored in this struct.

please refer to examples/example.go for example usages.

An example of a struct definition is shown as follows:

type Options struct {
    Help bool       `help:"Show help messages" short-token:"h"`
    Debug bool      `help:"Show extra debug information"`
    Timeout int     `default:"600" help:"Number of seconds to wait for a response"`
    SUBCOMMAND string `help:"subcommand" subcommand:"true"`
}

Argument name

Each member variable of the struct represents an argument. The variable name is the argument name.

Positional and optional arguments

If the variable name is all uppercased, the argument is a positional argument, otherwise, it is an optional argument. Additionally, boolean tag "optional" explicitly defines whether the argument is optional or positional.

Tags

The attributes of an argument are defined in the comment tags of the member variable of the struct. The following tags are supported:

	/*
	   help text of the argument
	   the argument is optional.
	*/
	TAG_HELP = "help"
	/*
	   command-line token for the optional argument, e.g. token:"url"
	   the command-line argument will be "--url http://127.0.0.1:3306"
	   the tag is optional.
	   if the tag is missing, the variable name will be used as token.
	   If the variable name is CamelCase, the token will be transformed
	   into kebab-case, e.g. if the variable is "AuthURL", the token will
	   be "--auth-url"
	*/
	TAG_TOKEN = "token"
	/*
	   short form of command-line token, e.g. short-token:"u"
	   the command-line argument will be "-u http://127.0.0.1:3306"
	   the tag is optional
	*/
	TAG_SHORT_TOKEN = "short-token"
	/*
	   Metavar of the argument
	   the tag is optional
	*/
	TAG_METAVAR = "metavar"
	/*
	   The default value of the argument.
	   the tag is optional
	*/
	TAG_DEFAULT = "default"
	/*
	   The possible values of an arguments. All choices are are concatenatd by "|".
	   e.g. `choices:"1|2|3"`
	   the tag is optional
	*/
	TAG_CHOICES = "choices"
	/*
	   A boolean value explicitly declare whether the argument is optional,
	   the tag is optional
	*/
	TAG_OPTIONAL = "optional"
	/*
	   A boolean value explicitly decalre whther the argument is an subcommand
	   A subcommand argument must be the last positional argument.
	   the tag is optional, the default value is false
	*/
	TAG_SUBCOMMAND = "subcommand"
	/*
	   The attribute defines the possible number of argument. Possible values
	   are:
	       * positive integers, e.g. "1", "2"
	       * "*" any number of arguments
	       * "+" at lease one argument
	       * "?" at most one argument
	   the tag is optional, the default value is "1"
	*/
	TAG_NARGS = "nargs"
	/*
		Alias name of argument
	*/
	TAG_ALIAS = "alias"

Example usage

use ParseArgs which set default value automatically

parser, e := structarg.NewArgumentParser(&Options{},
                                        "programname",
                                        `description text`,
                                        `epilog of the program`)

e = parser.ParseArgs(os.Args[1:], false)
if e != nil {
    panic(e)
}

options := parser.Options().(*Options)

// then access argument values via options
// ...

use ParseArgs2 which set default value according to parameter

call SetDefault() to set options default value

parser, e := structarg.NewArgumentParser(&Options{},
                                        "programname",
                                        `description text`,
                                        `epilog of the program`)

// do not set default value after parse
e = parser.ParseArgs2(os.Args[1:], false, false)
if e != nil {
    panic(e)
}

options := parser.Options().(*Options)

if len(options.Config) > 0 {
    e = parser.ParseFile(options.Config)
    if e != nil {
        panic(e)
    }
}

parser.SetDefault() // set option default here

// then access argument values via options
// ...