You may get an error like Parse error processing dependency '30log >= 0.8' if you use luarocks 2.1 or older. In this case, either upgrade to at least luarocks 2.1.1 or install 30log manually, then download the rockspec for argparse, remove the line "30log >= 0.8" and run

$ luarocks install /path/to/argparse/rockspec

Without luarocks

Download /src/argparse.lua file and put it into the directory for libraries or your working directory. Install 30log using luarocks or manually download 30log.lua file from 30log repo.

Tutorial

Creating a parser

The module contains the Parser class. To create an instance, call it or its :new() method.

-- script.lua
local argparse = require "argparse"
local parser = argparse()

parser is now an empty parser which does not recognize any command line arguments or options.

Parsing command line arguments

:parse([cmdline]) method of the Parser class returns a table with processed data from the command line or cmdline array.

local args = parser:parse()
for k, v in pairs(args) do print(k, v) end

When executed, this script prints nothing because the parser is empty and no command line arguments were supplied.

$ lua script.lua

Error handling

If the provided command line arguments are not recognized by the parser, it will print an error message and call os.exit(1).

$ lua script.lua foo

Usage: script.lua [-h]

Error: too many arguments

If halting the program is undesirable, :pparse([cmdline]) method should be used. It returns boolean flag indicating success of parsing and result or error message.

An error can raised manually using :error() method.

parser:error("manual argument validation failed")

Usage: script.lua [-h]

Error: manual argument validation failed

Help option

As the automatically generated usage message states, there is a help option -h added to any parser by default.

When a help option is used, parser will print a help message and call os.exit(0).

$ lua script.lua -h

Usage: script.lua [-h]

Options: 
   -h, --help            Show this help message and exit.

Typo autocorrection

When an option is not recognized by the parser, but there is an option with a similar name, a suggestion is automatically added to the error message.

$ lua script.lua --hepl

Usage: script.lua [-h]

Error: unknown option '--hepl'
Did you mean '--help'?

Configuring parser

Parsers have several fields affecting their behavior. For example, description field sets the text to be displayed in the help message between the usage message and the listings of options and arguments. Another is name, which overwrites the name of the program which is used in the usage message(default value is inferred from command line arguments).

There are several ways to set fields. The first is to call a parser with a table containing some fields.

local parser = argparse() {
   name = "script",
   description = "A testing script. "
}

The second is to chain setter methods of Parser object.

local parser = argparse()
   :name "script"
   :description "A testing script. "

As a special case, name field can be set by calling a parser with a string.

local parser = argparse "script"
   :description "A testing script. "

Adding arguments

Positional arguments can be added using :argument() method. It returns an Argument instance, which can be configured in the same way as Parsers. The name field is required.

parser:argument "input" -- sugar for :argument():name "input"

$ lua script.lua foo

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 field.

Setting number of arguments

args field 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 passed, a table is used to store the data.

parser:argument "pair"
   :args(2)
   :description "A pair of arguments. "
parser:argument "optional"
   :args "?"
   :description "An optional argument. "

$ lua script.lua foo bar

pair	{foo, bar}

$ lua script2.lua foo bar baz

pair	{foo, bar}
optional	baz

Adding options

Options can be added using :option() method. It returns an Option instance, which can be configured in the same way as Parsers. The name field is required. An option can have several aliases, which can be set using aliases field or by continuously calling the Option instance.

parser:option "-f" "--from"

$ lua script.lua --from there
$ lua script.lua --from=there
$ lua script.lua -f there
$ lua script.lua -fthere

from	there

For an option, default index used to store data is the first 'long' alias (an alias starting with two control characters) or just the first alias, without control characters.

Sometimes it is useful to explicitly set the index using target field to improve readability of help messages.

parser:option "-f" "--from"
   :target "server"

$ lua script.lua --help

Usage: script.lua [-f <server>] [-h]

Options: 
   -f <server>, --from <server>
   -h, --help            Show this help message and exit.

$ lua script.lua --from there

server	there

Flags

Flags are almost identical to options, except that they don't take an argument by default.

parser:flag "-q" "--quiet"

$ lua script.lua -q

quiet	true

Control characters

The first characters of all aliases of all options of a parser form the set of control characters, used to distinguish options from arguments. Typically the set only consists of a hyphen.

Setting number of arguments

Just as arguments, options can be configured to take several command line arguments.

parser:option "--pair"
   :args(2)
parser:option "--optional"
   :args "?"

$ lua script3.lua --pair foo bar

pair	{foo, bar}

$ lua script3.lua --pair foo bar --optional

pair	{foo, bar}
optional	{}

$ lua script3.lua --optional=baz

optional	{baz}

Note that the data passed to optional option is stored in an array. That is necessary to distinguish whether the option was invoked without an argument or it was not invoked at all.

Setting number of invocations

For options, it is possible to control how many times they can be used. argparse uses count field to set how many times an option can be invoked. The value of the field is interpreted in the same way args is.

parser:option "-e" "--exclude"
   :count "*"

$ lua script.lua -eFOO -eBAR

exclude	{FOO, BAR}

If an option can be used more than once and it can consume more than one argument, the data is stored as an array of invocations, each being an array of arguments.

As a special case, if an option can be used more than once and it consumes no arguments(e.g. it's a flag), than the number of invocations is stored in associated field of the result table.

parser:flag "-v" "--verbose"
   :count "0-2"
   :target "verbosity"
   :description [[Sets verbosity level. 
-v: Report all warning. 
-vv: Report all debugging information. ]]

$ lua script.lua -vv

verbosity	2

Commands

A command is a subparser invoked when its name is passed as an argument. For example, in luarocks CLI install, make, build, etc. are commands. Each command has its own set of arguments and options.

Commands can be added using :command() method. Just as options, commands can have several aliases.

parser:command "install" "i"

If a command it used, true is stored in the corresponding field of the result table.

$ lua script.lua install

install	true

A typo will result in an appropriate error message:

$ lua script.lua instal

Usage: script.lua [-h] <command> ...

Error: unknown command 'instal'
Did you mean 'install'?

Adding elements to commands

The Command class is a subclass of the Parser class, so all the Parser's methods for adding elements work on commands, too.

local install = parser:command "install"
install:argument "rock"
install:option "-f" "--from"

$ lua script.lua install foo --from=bar

install	true
rock	foo
from	bar

Commands have their own usage and help messages.

$ lua script.lua install

Usage: script.lua install [-f <from>] [-h] <rock>

Error: too few arguments

$ lua script.lua install --help

Usage: script.lua install [-f <from>] [-h] <rock>

Arguments: 
   rock

Options: 
   -f <from>, --from <from>
   -h, --help            Show this help message and exit.

Making a command optional

By default, if a parser has commands, using one of them is obligatory.

local parser = argparse()
parser:command "install"

$ lua script.lua

Usage: script.lua [-h] <command> ...

Error: a command is required

This can be changed using the require_command field.

local parser = argparse()
   :require_command(false)
parser:command "install"

Now not using a command is not an error:

$ lua script.lua

produces nothing.

Default values

For arguments and options, if default field is set, its value is used as default argument.

parser:argument "input"
   :default "input.txt"

$ lua script.lua

input	input.txt

The existence of a default value is reflected in help message.

$ lua script.lua --help

Usage: script.lua [-h] [<input>]

Arguments: 
   input                 default: input.txt

Options: 
   -h, --help            Show this help message and exit.

Default values and options

Note that if an option is not invoked, its default value will not be stored.

parser:option "-o" "--output"
   :default "a.out"

$ lua script.lua -o

output	a.out

But

$ lua script.lua

produces nothing.

That is because by default options can be not used at all. If default value must be used even when the option is not invoked, make the invocation obligatory.

parser:option "-o" "--output"
   :default "a.out"
   :count(1)

$ lua script.lua

output	a.out

Converters

argparse can perform automatic validation and conversion on arguments. If convert field of an element is a function, it will be applied to all the arguments passed to it. The function should return nil and, optionally, an error message if conversion failed. Standard tonumber and io.open functions work exactly like that.

parser:argument "input"
   :convert(io.open)
parser:option "-t" "--times"
   :convert(tonumber)

$ lua script.lua foo.txt -t5

input	file (0xaddress)
times	5 (number)

$ lua script.lua nonexistent.txt

Usage: script.lua [-t <times>] [-h] <input>

Error: nonexistent.txt: No such file or directory

$ lua script.lua foo.txt --times=many

Usage: script.lua [-t <times>] [-h] <input>

Error: malformed argument 'many'

Table converters

If convert field of an element contains a table, arguments passed to it will be used as keys. If a key is missing, an error is raised.

parser:argument "choice"
   :convert {
      foo = "Something foo-related",
      bar = "Something bar-related"
   }

$ lua script.lua bar

choice	Something bar-related

$ lua script.lua baz

Usage: script.lua [-h] <choice>

Error: malformed argument 'baz'

Actions

argparse can trigger a callback when an option, argument or command is processed. The callback can be set using action field.

Action are mostly useful for creating flags triggering immediate reaction regardless of whether the rest of command line arguments are correct.

parser:flag "-v" "--version"
   :description "Show version info and exit. "
   :action(function()
      print("script.lua v1.0.0")
      os.exit(0)
   end)

$ lua script.lua -v

script.lua v1.0.0

This example would work even if the script had mandatory arguments.

Miscellaneous

Overwriting default help option

If the field add_help of a parser is set to false, no help option will be added to it. Otherwise, the value of the field will be used to configure it.

local parser = argparse()
   :add_help {name = "/?"}

$ lua script.lua /?

Usage: script.lua [/?]

Options: 
   /?                    Show this help message and exit.

Configuring usage and help messages

Description and epilog

The value of description field of a parser is placed between the usage message and the argument list in the help message.

The value of epilog field is appended to the help message.

local parser = argparse "script"
   :description "A description. "
   :epilog "An epilog. "

$ lua script.lua --help

Usage: script [-h]

A description. 

Options: 
   -h, --help            Show this help message and exit. 

An epilog.

Argument placeholder

For options and arguments, argname field controls the placeholder for the argument in the usage message.

parser:option "-f" "--from"
   :argname "<server>"

$ lua script.lua --help

Usage: script.lua [-f <server>] [-h]

Options: 
   -f <server>, --from <server>
   -h, --help            Show this help message and exit.

Prohibiting overuse of options

By default, if an option is invoked too many times, latest invocations overwrite the data passed earlier.

parser:option "-o" "--output"

$ lua script.lua -oFOO -oBAR

output   BAR

Set the overwrite field to false to prohibit this behavior.

parser:option "-o" "--output"
   :overwrite(false)

$ lua script.lua -oFOO -oBAR

Usage: script.lua [-o <output>] [-h]

Error: option '-o' must be used at most 1 time

Documentation

Documentation is not available in the doc directory and online. If argparse was installed using luarocks 2.1.2 or later, it can not be viewed using luarocks doc argparse command.

Testing

argparse comes with a testing suite located in spec directory. busted is required for testing, it can be installed using luarocks. Run the tests using busted spec command from the argparse folder.