argparse: Command line optional and positional argument parser argparse hex sticker

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argparse is an R package which provides a command line parser to be used with Rscript to write “#!” shebang scripts that gracefully accept positional and optional arguments and automatically generate usage.

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

> install.packages("argparse")

To install the development version use the following command:

> remotes::install_github("trevorld/r-argparse")


The package has a Python dependency. It is easily satisfied if you have Python (version 3.2 or higher) on your PATH. Read the INSTALL file for more information if this doesn’t describe you.

Additionally this package depends on the R packages R6, findpython, and jsonlite.

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:

sudo apt install pandoc


> library("argparse")
> parser <- ArgumentParser(description='Process some integers')
> parser$add_argument('integers', metavar='N', type="integer", nargs='+',
+                    help='an integer for the accumulator')
> parser$add_argument('--sum', dest='accumulate', action='store_const',
+                    const='sum', default='max',
+                    help='sum the integers (default: find the max)')
> parser$print_help()
usage: PROGRAM [-h] [--sum] N [N ...]

Process some integers

positional arguments:
  N           an integer for the accumulator

optional arguments:
  -h, --help  show this help message and exit
  --sum       sum the integers (default: find the max)

Default args for ArgumentParser()$parse_args are commandArgs(TRUE) which is what you’d want for an Rscript but not for interactive use:

> args <- parser$parse_args(c("--sum", "1", "2", "3")) 
> accumulate_fn <- get(args$accumulate)
> print(accumulate_fn(args$integers))
[1] 6

Beginning with version 2.0 argparse also supports argument groups:

> parser = ArgumentParser(prog='PROG', add_help=FALSE)
> group1 = parser$add_argument_group('group1', 'group1 description')
> group1$add_argument('foo', help='foo help')
> group2 = parser$add_argument_group('group2', 'group2 description')
> group2$add_argument('--bar', help='bar help')
> parser$print_help()
usage: PROG [-h] [--bar BAR] foo

optional arguments:
  -h, --help  show this help message and exit

  group1 description

  foo         foo help

  group2 description

  --bar BAR   bar help

as well as mutually exclusive groups:

> parser = ArgumentParser(prog='PROG')
> group = parser$add_mutually_exclusive_group()
> group$add_argument('--foo', action='store_true')
> group$add_argument('--bar', action='store_false')
> parser$parse_args('--foo')
[1] TRUE

[1] TRUE

> parser$parse_args('--bar')

> parser$parse_args(c('--foo', '--bar'))
Error in "argparse::parse_args_output(output)" : parse error:
usage: PROG [-h] [--foo | --bar]
PROG: error: argument --bar: not allowed with argument --foo

and even basic support for sub-commands!:

> # create the top-level parser
> parser = ArgumentParser(prog='PROG')
> parser$add_argument('--foo', action='store_true', help='foo help')
> subparsers = parser$add_subparsers(help='sub-command help')

> # create the parser for the "a" command
> parser_a = subparsers$add_parser('a', help='a help')
> parser_a$add_argument('bar', type='integer', help='bar help')

> # create the parser for the "b" command
> parser_b = subparsers$add_parser('b', help='b help')
> parser_b$add_argument('--baz', choices='XYZ', help='baz help')

> # parse some argument lists
> parser$parse_args(c('a', '12'))
[1] 12


> parser$parse_args(c('--foo', 'b', '--baz', 'Z'))
[1] "Z"

[1] TRUE

> parser$print_help()
usage: PROG [-h] [--foo] {a,b} ...

positional arguments:
  {a,b}       sub-command help
    a         a help
    b         b help

optional arguments:
  -h, --help  show this help message and exit
  --foo       foo help

> parser_a$print_help()
usage: PROG a [-h] bar

positional arguments:
  bar         bar help

optional arguments:
  -h, --help  show this help message and exit

> parser_b$print_help()
usage: PROG b [-h] [--baz {X,Y,Z}]

optional arguments:
  -h, --help     show this help message and exit
  --baz {X,Y,Z}  baz help