package getopt

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Layout of the command line
Command line specification
Parsing the command line
Useful actions and handlers

package getopt

getopt
- Getopt

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Module Getopt: parsing of command line arguments.

email: Alain Frisch@ens.fr

web: http://www.eleves.ens.fr/home/frisch

This module provides a general mechanism for extracting options and arguments from the command line to the program. It is an alternative to the module Arg from the standard OCaml distribution.

The syntax is close to GNU getopt and getop_long (man 3 getopt).

Layout of the command line

There are two types of argument on the command line: options and anonymous arguments. Options may have two forms: a short one introduced by a single dash character (-) and a long one introduced by a double dash (--).

Options may have an argument attached. For the long form, the syntax is "--option=argument". For the short form, there are two possible syntaxes: "-o argument" (argument doesn't start with a dash) and "-oargument"

Short options that refuse arguments may be concatenated, as in "-opq".

The special argument -- interrupts the parsing of options: all the remaining arguments are arguments even they start with a dash.

Command line specification

A specification lists the possible options and describe what to do when they are found; it also gives the action for anonymous arguments and for the special option - (a single dash alone).

type opt = char * string * (unit -> unit) option * (string -> unit) option

The specification for a single option is a tuple (short_form, long_form, action, handler) where:

short_form is the character for the short form of the option without the leading - (or noshort='\000' if the option does not have a short form)

long_form is the string for the long form of the option without the leading -- (or nolong="" if no long form)

(action : (unit -> unit) option) gives the action to be executed when the option is found without an argument

(handler : (string -> unit) option) specifies how to handle the argument when the option is found with the argument

According to the pair (action, handler), the corresponding option may, must or mustn't have an argument :

(Some _, Some _) : the option may have an argument; the short form can't be concatenated with other options (even if the user does not want to provide an argument). The behaviour (handler/action) is determined by the presence of the argument.

(Some _, None) : the option must not have an argument; the short form, if it exists, may be concatenated

(None, Some _) : the option must have an argument; the short form can't be concatenated

(None, None) : not allowed

val noshort : char

noshort='\000' can be used when an option has no short form

val nolong : string

nolong="" can be used when an option has no long form

exception Error of string

Signals error on the command line

Parsing the command line

val parse : opt list -> (string -> unit) -> string array -> int -> int -> unit

parse opts others args first last parse the arguments args.(first), arg.(first+1) ... args.(last). others is called on anonymous arguments (and the special - argument); opts is a list of option specifications (there must be no ambiguities).

raises Error
: Unknown options, unexpected argument, ...

val parse_cmdline : opt list -> (string -> unit) -> unit

Parse the command line in Sys.argv using parse.

Useful actions and handlers

val set : 'a ref -> 'a -> (unit -> unit) option

returns
an action that gives a reference a given value

val incr : int ref -> (unit -> unit) option

returns
an action that increments an int reference

val append : string list ref -> (string -> unit) option

returns
an handler that appends the argument to the end of a string list reference

val atmost_once : string ref -> exn -> (string -> unit) option

returns
an handler that stores the argument in a string reference if it is empty, raises an exception otherwise