README.Rrst

optparse: Command line optional argument parser
===============================================

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   <img src="man/figures/logo.png" align="right" width="200px" alt="optparse hex sticker">

A pure R language command line parser inspired by Python's 'optparse' library to
be used with Rscript to write "#!" shebang scripts that accept short and
long flag/options.

To install the last version released on CRAN use the following command:

.. code:: r

    install.packages("optparse")

To install the development version use the following command:

.. code:: r

    install.packages("remotes")
    remotes::install_github("trevorld/r-optparse")

dependencies
------------

This package depends on the R package ``getopt``.

To run the unit tests you will need the suggested R package ``testthat`` and in
order to build the vignette you will need the suggested R package ``knitr`` 
which in turn probably requires the system tool ``pandoc``:

.. code:: bash

    sudo apt install pandoc

examples
--------

A simple example:

.. {r simple_example}

    library("optparse")
    parser <- OptionParser()
    parser <- add_option(parser, c("-v", "--verbose"), action="store_true", 
                    default=TRUE, help="Print extra output [default]")
    parser <- add_option(parser, c("-q", "--quietly"), action="store_false", 
                        dest="verbose", help="Print little output")
    parser <- add_option(parser, c("-c", "--count"), type="integer", default=5, 
                    help="Number of random normals to generate [default %default]",
                    metavar="number")
    parse_args(parser, args = c("--quietly", "--count=15"))
.. ..


Note that the ``args`` argument of ``parse_args`` default is ``commandArgs(trailing=TRUE)``
so it typically doesn't need to be explicitly set if writing an Rscript.

One can also equivalently make options in a list:

.. {r list_example}
    library("optparse")
    option_list <- list( 
        make_option(c("-v", "--verbose"), action="store_true", default=TRUE,
            help="Print extra output [default]"),
        make_option(c("-q", "--quietly"), action="store_false", 
            dest="verbose", help="Print little output"),
        make_option(c("-c", "--count"), type="integer", default=5, 
            help="Number of random normals to generate [default %default]",
            metavar="number")
        )
                                        
    parse_args(OptionParser(option_list=option_list), args = c("--verbose", "--count=11"))
.. ..

``optparse`` automatically creates a help option:

.. code:: r

    parse_args(parser, args = c("--help"))

::

    Usage: %prog [options]
    
    
    Options:
    	-h, --help
    		Show this help message and exit
    
    	-v, --verbose
    		Print extra output [default]
    
    	-q, --quietly
    		Print little output
    
    	-c NUMBER, --count=NUMBER
    		Number of random normals to generate [default 5]


    Error in parse_args(parser, args = c("--help")) : help requested

Note by default when ``optparse::parse_args`` sees a ``--help`` flag it will first print out a usage message and then either throw an error in interactive use or call ``quit`` in non-interactive use (i.e. when used within an Rscript called by a shell).  To disable the error/quit set the argument ``print_help_and_exit`` to ``FALSE`` in ``parse_args`` and to simply print out the usage string one can also use the function ``print_usage``.

``optparse`` has limited positional argument support, other command-line parsers for R such as ``argparse``
have richer positional argument support:

.. {r positional_example}
    parse_args(parser, args = c("-vc", "25", "75", "22"), positional_arguments = TRUE)
.. ..

The function ``parse_args2`` wraps ``parse_args`` while setting ``positional_arguments=TRUE`` and ``convert_hyphens_to_underscores=TRUE``:

.. {r parse_args2}

    parse_args2(parser, args = c("-vc", "25", "75", "22"))
.. ..