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Adding and configuring arguments
================================
Positional arguments can be added using ``:argument(name, description, default, convert, args)`` method. It returns an Argument instance, which can be configured in the same way as Parsers. The ``name`` property is required.
This and the following examples show contents of the result table returned by `parser:parse()` when the script is executed with given command-line arguments.
.. code-block:: lua
:linenos:
parser:argument "input"
.. code-block:: none
$ lua script.lua foo
.. code-block:: lua
{
input = "foo"
}
The data passed to the argument is stored in the result table at index ``input`` because it is the argument's name. The index can be changed using ``target`` property.
Setting number of consumed arguments
------------------------------------
``args`` property sets how many command line arguments the argument consumes. Its value is interpreted as follows:
================================================= =============================
Value Interpretation
================================================= =============================
Number ``N`` Exactly ``N`` arguments
String ``A-B``, where ``A`` and ``B`` are numbers From ``A`` to ``B`` arguments
String ``N+``, where ``N`` is a number ``N`` or more arguments
String ``?`` An optional argument
String ``*`` Any number of arguments
String ``+`` At least one argument
================================================= =============================
If more than one argument can be consumed, a table is used to store the data.
.. code-block:: lua
:linenos:
parser:argument("pair", "A pair of arguments.")
:args(2)
parser:argument("optional", "An optional argument.")
:args "?"
.. code-block:: none
$ lua script.lua foo bar
.. code-block:: lua
{
pair = {"foo", "bar"}
}
.. code-block:: none
$ lua script.lua foo bar baz
.. code-block:: lua
{
pair = {"foo", "bar"},
optional = "baz"
}
Setting argument choices
------------------------
The ``choices`` property can be used to restrict an argument to a set of choices. Its value is an array of string choices.
.. code-block:: lua
:linenos:
parser:argument "direction"
:choices {"north", "south", "east", "west"}
.. code-block:: none
$ lua script.lua foo
.. code-block:: none
Usage: script.lua [-h] {north,south,east,west}
Error: argument 'direction' must be one of 'north', 'south', 'east', 'west'
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