Module Arg
structure Arg = struct ... 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,
Set,
Clear,
String,
Int,
Float, and
Rest.
Unit,
Set and
Clear keywords take
no argument.
String,
Int, and
Float keywords take the following
word on the command line as an argument. A
Rest keyword takes the
remaining of the command line as (string) arguments.
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 *)
| Set of bool ref (* Set the reference to true *)
| Clear of bool ref (* Set the reference to false *)
| String of string -> unit (* Call the function with a string argument *)
| Int of int -> unit (* Call the function with an int argument *)
| Float of real -> unit (* Call the function with a float argument *)
| 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.
val parse : (string * spec * string) list -> (string -> unit) -> string -> unit
Arg.parse speclist anonfun 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.
anonfun is called on anonymous arguments.
The functions in
spec and
anonfun 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 anonfun, 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.
exception Bad of string
Functions in spec or anonfun can raise Arg.Bad with an error
message to reject invalid arguments.
val usage : (string * spec * string) list -> string -> 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 current : int 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.