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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. For example:

            let usage_msg = "append [-verbose] <file1> [<file2>] ... -o <output>"
            let verbose = ref false
            let input_files = ref []
            let output_file = ref ""

            let anon_fun filename =
              input_files := filename::!input_files

            let speclist =
              [("-verbose", Arg.Set verbose, "Output debug information");
               ("-o", Arg.Set_string output_file, "Set output file name")]

            let () =
              Arg.parse speclist anon_fun usage_msg;
              (* Main functionality here *)

       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 ,  Rest
       , Rest_all and Expand .

       Unit , Set and Clear keywords take no argument.

       A  Rest  or  Rest_all  keyword takes the remainder of the command line as arguments. (More
       explanations below.)

       Every other keyword takes the following  word  on  the  command  line  as  argument.   For
       compatibility  with  GNU getopt_long, keyword=arg is also allowed.  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)

       Rest takes a function that is called repeatedly for each remaining command line  argument.
       Rest_all takes a function that is called once, with the list of all remaining arguments.

       Note  that  if  no  arguments follow a Rest keyword then the function is not called at all
       whereas the function for a Rest_all keyword is called with an empty list.

       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 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
        *)
        | Set_string of string ref
         (* Set the reference to the string argument
        *)
        | Int of (int -> unit)
         (* Call the function with an int argument
        *)
        | Set_int of int ref
         (* Set the reference to the int argument
        *)
        | Float of (float -> unit)
         (* Call the function with a float argument
        *)
        | Set_float of float 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
        *)
        | Rest_all of (string list -> unit)
         (* Stop interpreting keywords and call the function with all remaining arguments
        *)
        | Expand of (string -> string array)
         (* If the remaining arguments to process are of the form ["-foo"; "arg"]  @  rest  where
       "foo"  is  registered  as Expand f , then the arguments f "arg" @ rest are processed. Only
       allowed in parse_and_expand_argv_dynamic .
        *)

       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.   Beware:  options
       that have an empty doc string will not be included in the list.

       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_dynamic : (key * spec * doc) list ref -> anon_fun -> usage_msg -> unit

       Same as Arg.parse , except that the speclist argument is a reference and  may  be  updated
       during the parsing. A typical use for this feature is to parse command lines of the form:

       -     command  subcommand  options  where  the list of options depends on the value of the
       subcommand argument.

       Since 4.01.0

       val parse_argv : ?current:int 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.

       val parse_argv_dynamic : ?current:int ref -> string array -> (key * spec * doc)  list  ref
       -> anon_fun -> string -> unit

       Same  as  Arg.parse_argv  ,  except  that  the speclist argument is a reference and may be
       updated during the parsing.  See Arg.parse_dynamic .

       Since 4.01.0

       val parse_and_expand_argv_dynamic : int ref -> string array ref -> (key * spec * doc) list
       ref -> anon_fun -> string -> unit

       Same  as  Arg.parse_argv_dynamic , except that the argv argument is a reference and may be
       updated during the parsing of Expand arguments.  See Arg.parse_argv_dynamic .

       Since 4.05.0

       val parse_expand : (key * spec * doc) list -> anon_fun -> usage_msg -> unit

       Same as Arg.parse , except that the Expand  arguments  are  allowed  and  the  Arg.current
       reference is not updated.

       Since 4.05.0

       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
       parameters.

       val align : ?limit:int -> (key * spec * doc) list -> (key * spec * doc) list

       Align  the documentation strings by inserting spaces at the first alignment separator (tab
       or, if tab is not found, space), according to the length of the keyword.  Use a  alignment
       separator  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 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.

       val read_arg : string -> string array

       Arg.read_arg file reads newline-terminated command line arguments from file file .

       Since 4.05.0

       val read_arg0 : string -> string array

       Identical to Arg.read_arg but assumes null character terminated command line arguments.

       Since 4.05.0

       val write_arg : string -> string array -> unit

       Arg.write_arg  file args writes the arguments args newline-terminated into the file file .
       If the any of the arguments in args contains a newline, use Arg.write_arg0 instead.

       Since 4.05.0

       val write_arg0 : string -> string array -> unit

       Identical to Arg.write_arg but uses the null character for terminator instead of newline.

       Since 4.05.0