Arg(3)

NAME
Arg - Parsing of command line arguments.

Module
Module Arg

Documentation

Module Arg
 : sig end

Parsing of command line arguments.

This module provides a general mechanism for extracting options and arguments from the command line to the program.

Syntax of command lines: A keyword is a character string starting with a - . An option is a keyword alone or followed by an argument. The types of keywords are: Unit , Bool , Set , Clear , String , Set_string , Int , Set_int , Float , Set_float , Tuple , Symbol , and Rest . Unit , Set and Clear keywords take no argument. A Rest keyword takes the remaining of the command line as arguments. Every other keyword takes the following word on the command line as argument. Arguments not preceded by a keyword are called anonymous arguments.

Examples ( cmd is assumed to be the command name):

- cmd -flag (a unit option)

- cmd -int 1 (an int option with argument 1 )

- cmd -string foobar (a string option with argument foobar )

- cmd -float 12.34 (a float option with argument 12.34 )

- cmd a b c (three anonymous arguments: a , b , and c )

- cmd a b -- c d (two anonymous arguments and a rest option with two arguments)

type spec =
 | Unit of (unit -> unit) (* Call the function with unit argument *)
 | Bool of (bool -> unit) (* Call the function with a bool argument *)
 | Set of bool Pervasives.ref (* Set the reference to true *)
 | Clear of bool Pervasives.ref (* Set the reference to false *)
 | String of (string -> unit) (* Call the function with a string argument *)
 | Set_string of string Pervasives.ref (* Set the reference to the string argument *)
 | Int of (int -> unit) (* Call the function with an int argument *)
 | Set_int of int Pervasives.ref (* Set the reference to the int argument *)
 | Float of (float -> unit) (* Call the function with a float argument *)
 | Set_float of float Pervasives.ref (* Set the reference to the float argument *)
 | Tuple of spec list (* Take several arguments according to the spec list *)
 | Symbol of string list * (string -> unit) (* Take one of the symbols as argument and call the function with the symbol *)
 | Rest of (string -> unit) (* Stop interpreting keywords and call the function with each remaining argument *)

The concrete type describing the behavior associated with a keyword.

type key = string

type doc = string

type usage_msg = string

type anon_fun = string -> unit

val parse : (key * spec * doc) list -> anon_fun -> usage_msg -> unit

Arg.parse speclist anon_fun usage_msg parses the command line. speclist is a list of triples (key, spec, doc) . key is the option keyword, it must start with a '-' character. spec gives the option type and the function to call when this option is found on the command line. doc is a one-line description of this option. anon_fun is called on anonymous arguments. The functions in spec and anon_fun are called in the same order as their arguments appear on the command line.

If an error occurs, Arg.parse exits the program, after printing an error message as follows:

- The reason for the error: unknown option, invalid or missing argument, etc.

- usage_msg

- The list of options, each followed by the corresponding doc string. For the user to be able to specify anonymous arguments starting with a - , include for example ("-", String anon_fun, doc) in speclist .

By default, parse recognizes two unit options, -help and --help , which will display usage_msg and the list of options, and exit the program. You can override this behaviour by specifying your own -help and --help options in speclist .

val parse_argv : ?current:int Pervasives.ref -> string array -> (key * spec * doc) list -> anon_fun -> usage_msg -> unit

Arg.parse_argv ~current args speclist anon_fun usage_msg parses the array args as if it were the command line. It uses and updates the value of ~current (if given), or Arg.current . You must set it before calling parse_argv . The initial value of current is the index of the program name (argument 0) in the array. If an error occurs, Arg.parse_argv raises Arg.Bad with the error message as argument. If option -help or --help is given, Arg.parse_argv raises Arg.Help with the help message as argument.

exception Help of string

Raised by Arg.parse_argv when the user asks for help.

exception Bad of string

Functions in spec or anon_fun can raise Arg.Bad with an error message to reject invalid arguments. Arg.Bad is also raised by Arg.parse_argv in case of an error.

val usage : (key * spec * doc) list -> usage_msg -> unit

Arg.usage speclist usage_msg prints an error message including the list of valid options. This is the same message that Arg.parse prints in case of error. speclist and usage_msg are the same as for Arg.parse .

val align : (key * spec * doc) list -> (key * spec * doc) list

Align the documentation strings by inserting spaces at the first space, according to the length of the keyword. Use a space as the first character in a doc string if you want to align the whole string. The doc strings corresponding to Symbol arguments are aligned on the next line.

val current : int Pervasives.ref

Position (in Sys.argv ) of the argument being processed. You can change this value, e.g. to force Arg.parse to skip some arguments. Arg.parse uses the initial value of Arg.current as the index of argument 0 (the program name) and starts parsing arguments at the next element.