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       Arg - Parsing of command line arguments.


       Module   Arg


       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

       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 to standard error 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 print to
       standard output 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 to standard error an error message that  includes  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 usage_string : (key * spec * doc) list -> usage_msg -> string

       Returns the message that would have been printed by Arg.usage , if provided with the  same

       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.