.TH "Arg" 3o 2023-09-18 OCamldoc "OCaml library"
.SH NAME
Arg \- Parsing of command line arguments.
.SH Module
Module   Arg
.SH Documentation
.sp
Module
.BI "Arg"
 : 
.B sig end

.sp
Parsing of command line arguments\&.
.sp
This module provides a general mechanism for extracting options and
arguments from the command line to the program\&. For example:
.sp

.EX
.ft B
.br
\&     let usage_msg = "append [\-verbose] <file1> [<file2>] \&.\&.\&. \-o <output>"
.br
\&     let verbose = ref false
.br
\&     let input_files = ref []
.br
\&     let output_file = ref ""
.br
\&
.br
\&     let anon_fun filename =
.br
\&       input_files := filename::!input_files
.br
\&
.br
\&     let speclist =
.br
\&       [("\-verbose", Arg\&.Set verbose, "Output debug information");
.br
\&        ("\-o", Arg\&.Set_string output_file, "Set output file name")]
.br
\&
.br
\&     let () =
.br
\&       Arg\&.parse speclist anon_fun usage_msg;
.br
\&       (* Main functionality here *)
.br
\&
.ft R
.EE
.sp
Syntax of command lines:
A keyword is a character string starting with a 
.ft B
\-
.ft R
\&.
An option is a keyword alone or followed by an argument\&.
The types of keywords are: 
.ft B
Unit
.ft R
, 
.ft B
Bool
.ft R
, 
.ft B
Set
.ft R
, 
.ft B
Clear
.ft R
,
.ft B
String
.ft R
, 
.ft B
Set_string
.ft R
, 
.ft B
Int
.ft R
, 
.ft B
Set_int
.ft R
, 
.ft B
Float
.ft R
, 
.ft B
Set_float
.ft R
,
.ft B
Tuple
.ft R
, 
.ft B
Symbol
.ft R
, 
.ft B
Rest
.ft R
, 
.ft B
Rest_all
.ft R
and 
.ft B
Expand
.ft R
\&.
.sp

.ft B
Unit
.ft R
, 
.ft B
Set
.ft R
and 
.ft B
Clear
.ft R
keywords take no argument\&.
.sp
A 
.ft B
Rest
.ft R
or 
.ft B
Rest_all
.ft R
keyword takes the remainder of the command line
as arguments\&. (More explanations below\&.)
.sp
Every other keyword takes the following word on the command line
as argument\&.  For compatibility with GNU getopt_long, 
.ft B
keyword=arg
.ft R
is also allowed\&.
Arguments not preceded by a keyword are called anonymous arguments\&.
.sp
Examples (
.ft B
cmd
.ft R
is assumed to be the command name):
.sp
\-  
.ft B
cmd \-flag           
.ft R
(a unit option)
.sp
\-  
.ft B
cmd \-int 1          
.ft R
(an int option with argument 
.ft B
1
.ft R
)
.sp
\-  
.ft B
cmd \-string foobar  
.ft R
(a string option with argument 
.ft B
"foobar"
.ft R
)
.sp
\-  
.ft B
cmd \-float 12\&.34    
.ft R
(a float option with argument 
.ft B
12\&.34
.ft R
)
.sp
\-  
.ft B
cmd a b c           
.ft R
(three anonymous arguments: 
.ft B
"a"
.ft R
, 
.ft B
"b"
.ft R
, and 
.ft B
"c"
.ft R
)
.sp
\-  
.ft B
cmd a b \-\- c d      
.ft R
(two anonymous arguments and a rest option with
two arguments)

.ft B
Rest
.ft R
takes a function that is called repeatedly for each
remaining command line argument\&. 
.ft B
Rest_all
.ft R
takes a function that
is called once, with the list of all remaining arguments\&.
.sp
Note that if no arguments follow a 
.ft B
Rest
.ft R
keyword then the function
is not called at all whereas the function for a 
.ft B
Rest_all
.ft R
keyword
is called with an empty list\&.

.sp

.sp
.sp
.I type spec 
=
 | Unit
.B of 
.B (unit -> unit)
.I "  "
  (* Call the function with unit argument
 *)
 | Bool
.B of 
.B (bool -> unit)
.I "  "
  (* Call the function with a bool argument
 *)
 | Set
.B of 
.B bool ref
.I "  "
  (* Set the reference to true
 *)
 | Clear
.B of 
.B bool ref
.I "  "
  (* Set the reference to false
 *)
 | String
.B of 
.B (string -> unit)
.I "  "
  (* Call the function with a string argument
 *)
 | Set_string
.B of 
.B string ref
.I "  "
  (* Set the reference to the string argument
 *)
 | Int
.B of 
.B (int -> unit)
.I "  "
  (* Call the function with an int argument
 *)
 | Set_int
.B of 
.B int ref
.I "  "
  (* Set the reference to the int argument
 *)
 | Float
.B of 
.B (float -> unit)
.I "  "
  (* Call the function with a float argument
 *)
 | Set_float
.B of 
.B float ref
.I "  "
  (* Set the reference to the float argument
 *)
 | Tuple
.B of 
.B spec list
.I "  "
  (* Take several arguments according to the
spec list
 *)
 | Symbol
.B of 
.B string list * (string -> unit)
.I "  "
  (* Take one of the symbols as argument and
call the function with the symbol
 *)
 | Rest
.B of 
.B (string -> unit)
.I "  "
  (* Stop interpreting keywords and call the
function with each remaining argument
 *)
 | Rest_all
.B of 
.B (string list -> unit)
.I "  "
  (* Stop interpreting keywords and call the
function with all remaining arguments
 *)
 | Expand
.B of 
.B (string -> string array)
.I "  "
  (* If the remaining arguments to process
are of the form
.ft B
["\-foo"; "arg"] @ rest
.ft R
where "foo"
is registered as 
.ft B
Expand f
.ft R
, then the
arguments 
.ft B
f "arg" @ rest
.ft R
are
processed\&. Only allowed in
.ft B
parse_and_expand_argv_dynamic
.ft R
\&.
 *)
 
.sp
The concrete type describing the behavior associated
with a keyword\&.

.sp
.I type key 
= 
.B string

.sp

.sp
.I type doc 
= 
.B string

.sp

.sp
.I type usage_msg 
= 
.B string

.sp

.sp
.I type anon_fun 
= 
.B string -> unit

.sp

.sp

.I val parse 
: 
.B (key * spec * doc) list -> anon_fun -> usage_msg -> unit
.sp

.ft B
Arg\&.parse speclist anon_fun usage_msg
.ft R
parses the command line\&.
.ft B
speclist
.ft R
is a list of triples 
.ft B
(key, spec, doc)
.ft R
\&.
.ft B
key
.ft R
is the option keyword, it must start with a 
.ft B
\&'\-\&'
.ft R
character\&.
.ft B
spec
.ft R
gives the option type and the function to call when this option
is found on the command line\&.
.ft B
doc
.ft R
is a one\-line description of this option\&.
.ft B
anon_fun
.ft R
is called on anonymous arguments\&.
The functions in 
.ft B
spec
.ft R
and 
.ft B
anon_fun
.ft R
are called in the same order
as their arguments appear on the command line\&.
.sp
If an error occurs, 
.ft B
Arg\&.parse
.ft R
exits the program, after printing
to standard error an error message as follows:
.sp
\-  The reason for the error: unknown option, invalid or missing argument, etc\&.
.sp
\-  
.ft B
usage_msg
.ft R

.sp
\-  The list of options, each followed by the corresponding 
.ft B
doc
.ft R
string\&.
Beware: options that have an empty 
.ft B
doc
.ft R
string will not be included in the
list\&.

For the user to be able to specify anonymous arguments starting with a
.ft B
\-
.ft R
, include for example 
.ft B
("\-", String anon_fun, doc)
.ft R
in 
.ft B
speclist
.ft R
\&.
.sp
By default, 
.ft B
parse
.ft R
recognizes two unit options, 
.ft B
\-help
.ft R
and 
.ft B
\-\-help
.ft R
,
which will print to standard output 
.ft B
usage_msg
.ft R
and the list of
options, and exit the program\&.  You can override this behaviour
by specifying your own 
.ft B
\-help
.ft R
and 
.ft B
\-\-help
.ft R
options in 
.ft B
speclist
.ft R
\&.

.sp

.I val parse_dynamic 
: 
.B (key * spec * doc) list ref ->
.B   anon_fun -> usage_msg -> unit
.sp
Same as 
.ft B
Arg\&.parse
.ft R
, except that the 
.ft B
speclist
.ft R
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:
.sp
\-    command subcommand 
.ft B
options
.ft R
where the list of options depends on the value of the subcommand argument\&.


.sp
.B "Since"
4.01.0

.sp

.I val parse_argv 
: 
.B ?current:int ref ->
.B   string array ->
.B   (key * spec * doc) list -> anon_fun -> usage_msg -> unit
.sp

.ft B
Arg\&.parse_argv ~current args speclist anon_fun usage_msg
.ft R
parses
the array 
.ft B
args
.ft R
as if it were the command line\&.  It uses and updates
the value of 
.ft B
~current
.ft R
(if given), or 
.ft B
Arg\&.current
.ft R
\&.  You must set
it before calling 
.ft B
parse_argv
.ft R
\&.  The initial value of 
.ft B
current
.ft R
is the index of the program name (argument 0) in the array\&.
If an error occurs, 
.ft B
Arg\&.parse_argv
.ft R
raises 
.ft B
Arg\&.Bad
.ft R
with
the error message as argument\&.  If option 
.ft B
\-help
.ft R
or 
.ft B
\-\-help
.ft R
is
given, 
.ft B
Arg\&.parse_argv
.ft R
raises 
.ft B
Arg\&.Help
.ft R
with the help message
as argument\&.

.sp

.I val parse_argv_dynamic 
: 
.B ?current:int ref ->
.B   string array ->
.B   (key * spec * doc) list ref ->
.B   anon_fun -> string -> unit
.sp
Same as 
.ft B
Arg\&.parse_argv
.ft R
, except that the 
.ft B
speclist
.ft R
argument is a
reference and may be updated during the parsing\&.
See 
.ft B
Arg\&.parse_dynamic
.ft R
\&.

.sp
.B "Since"
4.01.0

.sp

.I val parse_and_expand_argv_dynamic 
: 
.B int ref ->
.B   string array ref ->
.B   (key * spec * doc) list ref ->
.B   anon_fun -> string -> unit
.sp
Same as 
.ft B
Arg\&.parse_argv_dynamic
.ft R
, except that the 
.ft B
argv
.ft R
argument is a
reference and may be updated during the parsing of 
.ft B
Expand
.ft R
arguments\&.
See 
.ft B
Arg\&.parse_argv_dynamic
.ft R
\&.

.sp
.B "Since"
4.05.0

.sp

.I val parse_expand 
: 
.B (key * spec * doc) list -> anon_fun -> usage_msg -> unit
.sp
Same as 
.ft B
Arg\&.parse
.ft R
, except that the 
.ft B
Expand
.ft R
arguments are allowed and
the 
.ft B
Arg\&.current
.ft R
reference is not updated\&.

.sp
.B "Since"
4.05.0

.sp

.I exception Help 
.B of 
.B string

.sp
Raised by 
.ft B
Arg\&.parse_argv
.ft R
when the user asks for help\&.

.sp

.I exception Bad 
.B of 
.B string

.sp
Functions in 
.ft B
spec
.ft R
or 
.ft B
anon_fun
.ft R
can raise 
.ft B
Arg\&.Bad
.ft R
with an error
message to reject invalid arguments\&.
.ft B
Arg\&.Bad
.ft R
is also raised by 
.ft B
Arg\&.parse_argv
.ft R
in case of an error\&.

.sp

.I val usage 
: 
.B (key * spec * doc) list -> usage_msg -> unit
.sp

.ft B
Arg\&.usage speclist usage_msg
.ft R
prints to standard error
an error message that includes the list of valid options\&.  This is
the same message that 
.ft B
Arg\&.parse
.ft R
prints in case of error\&.
.ft B
speclist
.ft R
and 
.ft B
usage_msg
.ft R
are the same as for 
.ft B
Arg\&.parse
.ft R
\&.

.sp

.I val usage_string 
: 
.B (key * spec * doc) list -> usage_msg -> string
.sp
Returns the message that would have been printed by 
.ft B
Arg\&.usage
.ft R
,
if provided with the same parameters\&.

.sp

.I val align 
: 
.B ?limit:int ->
.B   (key * spec * doc) list -> (key * spec * doc) list
.sp
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 
.ft B
Symbol
.ft R
arguments are aligned on the next line\&.

.sp

.I val current 
: 
.B int ref
.sp
Position (in 
.ft B
Sys\&.argv
.ft R
) of the argument being processed\&.  You can
change this value, e\&.g\&. to force 
.ft B
Arg\&.parse
.ft R
to skip some arguments\&.
.ft B
Arg\&.parse
.ft R
uses the initial value of 
.ft B
Arg\&.current
.ft R
as the index of
argument 0 (the program name) and starts parsing arguments
at the next element\&.

.sp

.I val read_arg 
: 
.B string -> string array
.sp

.ft B
Arg\&.read_arg file
.ft R
reads newline\-terminated command line arguments from
file 
.ft B
file
.ft R
\&.

.sp
.B "Since"
4.05.0

.sp

.I val read_arg0 
: 
.B string -> string array
.sp
Identical to 
.ft B
Arg\&.read_arg
.ft R
but assumes null character terminated command
line arguments\&.

.sp
.B "Since"
4.05.0

.sp

.I val write_arg 
: 
.B string -> string array -> unit
.sp

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

.sp
.B "Since"
4.05.0

.sp

.I val write_arg0 
: 
.B string -> string array -> unit
.sp
Identical to 
.ft B
Arg\&.write_arg
.ft R
but uses the null character for terminator
instead of newline\&.

.sp
.B "Since"
4.05.0

.sp