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
Stop interpreting keywords and call the
function with each remaining argument
The concrete type describing the behavior associated
with a keyword.
valparse : (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.
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.
valparse_argv : string array -> (string * spec * string) list -> (string -> unit) -> string -> unit
Arg.parse_argv args speclist anonfun usage_msg parses array args as
if it were the command line.
Functions in spec or anonfun can raise Arg.Bad with an error
message to reject invalid arguments.
valusage : (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.