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Arg(3o) OCaml library Arg(3o)
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 argu-
ments.
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 com-
mand 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 argu-
ments appear on the command line.
If an error occurs, Arg.parse exits the program, after printing an error message as fol-
lows:
- 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.cur-
rent . 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.cur-
rent as the index of argument 0 (the program name) and starts parsing arguments at the
next element.
OCamldoc 2008-05-19 Arg(3o)
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