# Module Cmdliner.Arg

    module Arg: sig .. end

Terms for command line arguments.

This module provides functions to define terms that evaluate to the arguments provided on the command line.

Basic constraints, like the argument type or repeatability, are specified by defining a value of type `Cmdliner.Arg.t`. Further contraints can be specified during the conversion to a term.

# Argument converters

An argument converter transforms a string argument of the command line to an OCaml value. Predefined converters are provided for many types of the standard library.

    type 'a parser = string -> [ `Error of string | `Ok of 'a ]

The type for argument parsers.

    type 'a printer = Format.formatter -> 'a -> unit

The type for converted argument printers.

    type 'a converter = 'a parser * 'a printer

The type for argument converters.

    val some : ?none:string -> 'a converter -> 'a option converter

`some none c` is like the converter `c` except it returns `Some` value. It is used for command line arguments that default to `None` when absent. `none` is what to print to document the absence (defaults to `""`).

# Arguments and their information

Argument information defines the man page information of an argument and, for optional arguments, its names.

    type 'a t

The type for arguments holding data of type `'a`.

    type info

The type for information about command line arguments.

    val info : ?docs:string ->
           ?docv:string -> ?doc:string -> string list -> info

`info docs docv doc names` defines information for an argument.

`names` defines the names under which an optional argument can be referred to. Strings of length `1` (`"c"`) define short option names (`"-c"`), longer strings (`"count"`) define long option names (`"--count"`). `names` must be empty for positional arguments.

- `doc` is the man page information of the argument. The variable `"$(docv)"` can be used to refer to the value of `docv` (see below).
- `docv` is for positional and non-flag optional arguments. It is a variable name used in the man page to stand for their value.
- `docs` is the title of the man page section in which the argument will be listed. For optional arguments this defaults to `"OPTIONS"`. For positional arguments this defaults to `"ARGUMENTS"`. However a positional argument is only listed if it has both a `doc` and `docv` specified.

    val (&) : ('a -> 'b) -> 'a -> 'b

`f & v` is `f v`, a right associative composition operator for specifying argument terms.

# Optional arguments

The information of an optional argument must have at least one name or `Invalid_argument` is raised.

    val flag : info -> bool t

`flag i` is a `bool` argument defined by an optional flag that may appear at most once on the command line under one of the names specified by `i`. The argument holds `true` if the flag is present on the command line and `false` otherwise.

    val flag_all : info -> bool list t

`flag_all` is like `Cmdliner.Arg.flag` except the flag may appear more than once. The argument holds a list that contains one `true` value per occurence of the flag. It holds the empty list if the flag is absent from the command line.

    val vflag : 'a -> ('a * info) list -> 'a t

`vflag v [v`0`,i`0`;...]` is an `'a` argument defined by an optional flag that may appear at most once on the command line under one of the names specified in the `i`k values. The argument holds `v` if the flag is absent from the command line and the value `v`k if the name under which it appears is in `i`k.

    val vflag_all : 'a list -> ('a * info) list -> 'a list t

`vflag_all v l` is like `Cmdliner.Arg.vflag` except the flag may appear more than once. The argument holds the list `v` if the flag is absent from the command line. Otherwise it holds a list that contains one corresponding value per occurence of the flag, in the order found on the command line.

    val opt : ?vopt:'a ->
           'a converter -> 'a -> info -> 'a t

`opt vopt c v i` is an `'a` argument defined by the value of an optional argument that may appear at most once on the command line under one of the names specified by `i`. The argument holds `v` if the option is absent from the command line. Otherwise it has the value of the option as converted by `c`.

If `vopt` is provided the value of the optional argument is itself optional, taking the value `vopt` if unspecified on the command line.

    val opt_all : ?vopt:'a ->
           'a converter ->
           'a list -> info -> 'a list t

`opt_all vopt c v i` is like `Cmdliner.Arg.opt` except the optional argument may appear more than once. The argument holds a list that contains one value per occurence of the flag in the order found on the command line. It holds the list `v` if the flag is absent from the command line.

# Positional arguments

The information of a positional argument must have no name or `Invalid_argument` is raised. Positional arguments indexing is zero-based.

    val pos : ?rev:bool ->
           int ->
           'a converter -> 'a -> info -> 'a t

`pos rev n c v i` is an `'a` argument defined by the `n`th positional argument of the command line as converted by `c`. If the positional argument is absent from the command line the argument is `v`.

If `rev` is `true` (defaults to `false`), the computed position is `max-n` where `max` is the position of the last positional argument present on the command line.

    val pos_all : 'a converter ->
           'a list -> info -> 'a list t

`pos_all c v i` is an `'a list` argument that holds all the positional arguments of the command line as converted by `c` or `v` if there are none.

    val pos_left : ?rev:bool ->
           int ->
           'a converter ->
           'a list -> info -> 'a list t

`pos_left rev n c v i` is an `'a list` argument that holds all the positional arguments as converted by `c` found on the left of the `n`th positional argument or `v` if there are none.

If `rev` is `true` (defaults to `false`), the computed position is `max-n` where `max` is the position of the last positional argument present on the command line.

    val pos_right : ?rev:bool ->
           int ->
           'a converter ->
           'a list -> info -> 'a list t

`pos_right` is like `Cmdliner.Arg.pos_left` except it holds all the positional arguments found on the right of the specified positional argument.

# Arguments as terms

    val value : 'a t -> 'a Cmdliner.Term.t

`value a` is a term that evaluates to `a`'s value.

    val required : 'a option t -> 'a Cmdliner.Term.t

`required a` is a term that fails if `a`'s value is `None` and evaluates to the value of `Some` otherwise. Use this for required positional arguments (it can also be used for defining required optional arguments, but from a user interface perspective this shouldn't be done, it is a contradiction in terms).

    val non_empty : 'a list t -> 'a list Cmdliner.Term.t

`non_empty a` is term that fails if `a`'s list is empty and evaluates to `a`'s list otherwise. Use this for non empty lists of positional arguments.

    val last : 'a list t -> 'a Cmdliner.Term.t

`last a` is a term that fails if `a`'s list is empty and evaluates to the value of the last element of the list otherwise. Use this for lists of flags or options where the last occurence takes precedence over the others.

# Predefined converters

    val bool : bool converter

`bool` converts values with `bool_of_string`.

    val char : char converter

`char` converts values by ensuring the argument has a single char.

    val int : int converter

`int` converts values with `int_of_string`.

    val nativeint : nativeint converter

`nativeint` converts values with `Nativeint.of_string`.

    val int32 : int32 converter

`int32` converts values with `Int32.of_string`.

    val int64 : int64 converter

`int64` converts values with `Int64.of_string`.

    val float : float converter

`float` converts values with `float_of_string`.

    val string : string converter

`string` converts values with the identity function.

    val enum : (string * 'a) list -> 'a converter

`enum l p` converts values such that unambiguous prefixes of string names in `l` map to the corresponding value of type `'a`.

    val file : string converter

`file` converts a value with the identity function and checks with `Sys.file_exists` that a file with that name exists.

    val dir : string converter

`dir` converts a value with the identity function and checks with `Sys.file_exists` and `Sys.is_directory` that a directory with that name exists.

    val non_dir_file : string converter

`non_dir_file` converts a value with the identity function and checks with `Sys.file_exists` and `Sys.is_directory` that a non directory file with that name exists.

    val list : ?sep:char -> 'a converter -> 'a list converter

`list sep c` splits the argument at each `sep` (defaults to `','`) character and converts each substrings with `c`.

    val array : ?sep:char -> 'a converter -> 'a array converter

`array sep c` splits the argument at each `sep` (defaults to `','`) character and converts each substring with `c`.

    val pair : ?sep:char ->
           'a converter ->
           'b converter -> ('a * 'b) converter

`pair sep c0 c1` splits the argument at the first `sep` character (defaults to `','`) and respectively converts the substrings with `c0` and `c1`.

    val t2 : ?sep:char ->
           'a converter ->
           'b converter -> ('a * 'b) converter

`Cmdliner.Arg.t2` is `Cmdliner.Arg.pair`.

    val t3 : ?sep:char ->
           'a converter ->
           'b converter ->
           'c converter -> ('a * 'b * 'c) converter

`t3 sep c0 c1 c2` splits the argument at the first two `sep` characters (defaults to `','`) and respectively converts the substrings with `c0`, `c1` and `c2`.

    val t4 : ?sep:char ->
           'a converter ->
           'b converter ->
           'c converter ->
           'd converter -> ('a * 'b * 'c * 'd) converter

`t4 sep c0 c1 c2 c3` splits the argument at the first three `sep` characters (defaults to `','`) respectively converts the substrings with `c0`, `c1`, `c2` and `c3`.