@spec next(argv(), options()) ::
  {:ok, key :: atom(), value :: term(), argv()}
  | {:invalid, String.t(), String.t() | nil, argv()}
  | {:undefined, String.t(), String.t() | nil, argv()}
  | {:error, argv()}

Low-level function that parses one option.

It accepts the same options as parse/2 and parse_head/2 as both functions are built on top of this function. This function may return:

• {:ok, key, value, rest} - the option key with value was successfully parsed

• {:invalid, key, value, rest} - the option key is invalid with value (returned when the value cannot be parsed according to the switch type)

• {:undefined, key, value, rest} - the option key is undefined (returned in strict mode when the switch is unknown or on nonexistent atoms)

• {:error, rest} - there are no switches at the head of the given argv

@spec parse(argv(), options()) :: {parsed(), argv(), errors()}

Parses argv into a keyword list.

It returns a three-element tuple with the form {parsed, args, invalid}, where:

• parsed is a keyword list of parsed switches with {switch_name, value} tuples in it; switch_name is the atom representing the switch name while value is the value for that switch parsed according to opts (see the "Examples" section for more information)
• args is a list of the remaining arguments in argv as strings
• invalid is a list of invalid options as {option_name, value} where option_name is the raw option and value is nil if the option wasn't expected or the string value if the value didn't have the expected type for the corresponding option

Elixir converts switches to underscored atoms, so --source-path becomes :source_path. This is done to better suit Elixir conventions. However, this means that switches can't contain underscores and switches that do contain underscores are always returned in the list of invalid switches.

When parsing, it is common to list switches and their expected types:

iex> OptionParser.parse(["--debug"], strict: [debug: :boolean])
{[debug: true], [], []}

iex> OptionParser.parse(["--source", "lib"], strict: [source: :string])
{[source: "lib"], [], []}

iex> OptionParser.parse(
...>   ["--source-path", "lib", "test/enum_test.exs", "--verbose"],
...>   strict: [source_path: :string, verbose: :boolean]
...> )
{[source_path: "lib", verbose: true], ["test/enum_test.exs"], []}

We will explore the valid switches and operation modes of option parser below.

Options

The following options are supported:

• :switches or :strict - see the "Switch definitions" section below
• :allow_nonexistent_atoms - see the "Parsing unknown switches" section below
• :aliases - see the "Aliases" section below
• :return_separator - see the "Return separator" section below

Switch definitions

Switches can be specified via one of two options:

• :strict - defines strict switches and their types. Any switch in argv that is not specified in the list is returned in the invalid options list. This is the preferred way to parse options.

• :switches - defines switches and their types. This function still attempts to parse switches that are not in this list.

Both these options accept a keyword list where the key is an atom defining the name of the switch and value is the type of the switch (see the "Types" section below for more information).

Note that you should only supply the :switches or the :strict option. If you supply both, an ArgumentError exception will be raised.

Types

Switches parsed by OptionParser may take zero or one arguments.

The following switches types take no arguments:

• :boolean - sets the value to true when given (see also the "Negation switches" section below)
• :count - counts the number of times the switch is given

The following switches take one argument:

• :integer - parses the value as an integer
• :float - parses the value as a float
• :string - parses the value as a string

If a switch can't be parsed according to the given type, it is returned in the invalid options list.

Modifiers

Switches can be specified with modifiers, which change how they behave. The following modifiers are supported:

• :keep - keeps duplicate elements instead of overriding them; works with all types except :count. Specifying switch_name: :keep assumes the type of :switch_name will be :string.

To use :keep with a type other than :string, use a list as the type for the switch. For example: [foo: [:integer, :keep]].

Negation switches

In case a switch SWITCH is specified to have type :boolean, it may be passed as --no-SWITCH as well which will set the option to false:

iex> OptionParser.parse(["--no-op", "path/to/file"], switches: [op: :boolean])
{[op: false], ["path/to/file"], []}

Parsing unknown switches

When the :switches option is given, OptionParser will attempt to parse unknown switches.

Switches without an argument will be set to true:

iex> OptionParser.parse(["--debug"], switches: [key: :string])
{[debug: true], [], []}

Even though we haven't specified --debug in the list of switches, it is part of the returned options. The same happens for switches followed by another switch:

iex> OptionParser.parse(["--debug", "--ok"], switches: [])
{[debug: true, ok: true], [], []}

Switches followed by a value will be assigned the value, as a string:

iex> OptionParser.parse(["--debug", "value"], switches: [key: :string])
{[debug: "value"], [], []}

Since we cannot assert the type of the switch value, it is preferred to use the :strict option that accepts only known switches and always verify their types.

If you do want to parse unknown switches, remember that Elixir converts switches to atoms. Since atoms are not garbage-collected, to avoid creating new ones, OptionParser by default only parses switches that translate to existing atoms. The code below discards the --option-parser-example switch because the :option_parser_example atom is never used anywhere:

iex> OptionParser.parse(["--option-parser-example"], switches: [])
{[], [], []}

If a switch corresponds to an existing Elixir atom, whether from your code, a dependency or from Elixir itself, it will be accepted. However, it is best to not rely on external code, and always define the atoms you want to parse in the same module that calls OptionParser itself, as direct arguments to the :switches or :strict options.

If you would like to parse all switches, regardless if they exist or not, you can force creation of atoms by passing allow_nonexistent_atoms: true as option. Use this option with care. It is only useful when you are building command-line applications that receive dynamically-named arguments and must be avoided in long-running systems.

Aliases

A set of aliases can be specified in the :aliases option:

iex> OptionParser.parse(["-d"], aliases: [d: :debug], strict: [debug: :boolean])
{[debug: true], [], []}

Examples

Here are some examples of working with different types and modifiers:

iex> OptionParser.parse(["--unlock", "path/to/file"], strict: [unlock: :boolean])
{[unlock: true], ["path/to/file"], []}

iex> OptionParser.parse(
...>   ["--unlock", "--limit", "0", "path/to/file"],
...>   strict: [unlock: :boolean, limit: :integer]
...> )
{[unlock: true, limit: 0], ["path/to/file"], []}

iex> OptionParser.parse(["--limit", "3"], strict: [limit: :integer])
{[limit: 3], [], []}

iex> OptionParser.parse(["--limit", "xyz"], strict: [limit: :integer])
{[], [], [{"--limit", "xyz"}]}

iex> OptionParser.parse(["--verbose"], switches: [verbose: :count])
{[verbose: 1], [], []}

iex> OptionParser.parse(["-v", "-v"], aliases: [v: :verbose], strict: [verbose: :count])
{[verbose: 2], [], []}

iex> OptionParser.parse(["--unknown", "xyz"], strict: [])
{[], ["xyz"], [{"--unknown", nil}]}

iex> OptionParser.parse(
...>   ["--limit", "3", "--unknown", "xyz"],
...>   switches: [limit: :integer]
...> )
{[limit: 3, unknown: "xyz"], [], []}

iex> OptionParser.parse(
...>   ["--unlock", "path/to/file", "--unlock", "path/to/another/file"],
...>   strict: [unlock: :keep]
...> )
{[unlock: "path/to/file", unlock: "path/to/another/file"], [], []}

Return separator

The separator -- implies options should no longer be processed. By default, the separator is not returned as parts of the arguments, but that can be changed via the :return_separator option:

iex> OptionParser.parse(["--", "lib"], return_separator: true, strict: [])
{[], ["--", "lib"], []}

iex> OptionParser.parse(["--no-halt", "--", "lib"], return_separator: true, switches: [halt: :boolean])
{[halt: false], ["--", "lib"], []}

iex> OptionParser.parse(["script.exs", "--no-halt", "--", "foo"], return_separator: true, switches: [halt: :boolean])
{[{:halt, false}], ["script.exs", "--", "foo"], []}

@spec parse!(argv(), options()) :: {parsed(), argv()}

The same as parse/2 but raises an OptionParser.ParseError exception if any invalid options are given.

If there are no errors, returns a {parsed, rest} tuple where:

• parsed is the list of parsed switches (same as in parse/2)
• rest is the list of arguments (same as in parse/2)

Examples

iex> OptionParser.parse!(["--debug", "path/to/file"], strict: [debug: :boolean])
{[debug: true], ["path/to/file"]}

iex> OptionParser.parse!(["--limit", "xyz"], strict: [limit: :integer])
** (OptionParser.ParseError) 1 error found!
--limit : Expected type integer, got "xyz"

iex> OptionParser.parse!(["--unknown", "xyz"], strict: [])
** (OptionParser.ParseError) 1 error found!
--unknown : Unknown option

iex> OptionParser.parse!(
...>   ["-l", "xyz", "-f", "bar"],
...>   switches: [limit: :integer, foo: :integer],
...>   aliases: [l: :limit, f: :foo]
...> )
** (OptionParser.ParseError) 2 errors found!
-l : Expected type integer, got "xyz"
-f : Expected type integer, got "bar"

@spec parse_head(argv(), options()) :: {parsed(), argv(), errors()}

Similar to parse/2 but only parses the head of argv; as soon as it finds a non-switch, it stops parsing.

See parse/2 for more information.

Example

iex> OptionParser.parse_head(
...>   ["--source", "lib", "test/enum_test.exs", "--verbose"],
...>   switches: [source: :string, verbose: :boolean]
...> )
{[source: "lib"], ["test/enum_test.exs", "--verbose"], []}

iex> OptionParser.parse_head(
...>   ["--verbose", "--source", "lib", "test/enum_test.exs", "--unlock"],
...>   switches: [source: :string, verbose: :boolean, unlock: :boolean]
...> )
{[verbose: true, source: "lib"], ["test/enum_test.exs", "--unlock"], []}

@spec parse_head!(argv(), options()) :: {parsed(), argv()}

The same as parse_head/2 but raises an OptionParser.ParseError exception if any invalid options are given.

If there are no errors, returns a {parsed, rest} tuple where:

• parsed is the list of parsed switches (same as in parse_head/2)
• rest is the list of arguments (same as in parse_head/2)

Examples

iex> OptionParser.parse_head!(
...>   ["--source", "lib", "path/to/file", "--verbose"],
...>   switches: [source: :string, verbose: :boolean]
...> )
{[source: "lib"], ["path/to/file", "--verbose"]}

iex> OptionParser.parse_head!(
...>   ["--number", "lib", "test/enum_test.exs", "--verbose"],
...>   strict: [number: :integer]
...> )
** (OptionParser.ParseError) 1 error found!
--number : Expected type integer, got "lib"

iex> OptionParser.parse_head!(
...>   ["--verbose", "--source", "lib", "test/enum_test.exs", "--unlock"],
...>   strict: [verbose: :integer, source: :integer]
...> )
** (OptionParser.ParseError) 2 errors found!
--verbose : Missing argument of type integer
--source : Expected type integer, got "lib"

@spec split(String.t()) :: argv()

Splits a string into argv/0 chunks.

This function splits the given string into a list of strings in a similar way to many shells.

Examples

iex> OptionParser.split("foo bar")
["foo", "bar"]

iex> OptionParser.split("foo \"bar baz\"")
["foo", "bar baz"]

@spec to_argv(Enumerable.t(), options()) :: argv()

Receives a key-value enumerable and converts it to argv/0.

Keys must be atoms. Keys with nil value are discarded, boolean values are converted to --key or --no-key (if the value is true or false, respectively), and all other values are converted using to_string/1.

It is advised to pass to to_argv/2 the same set of options given to parse/2. Some switches can only be reconstructed correctly with the :switches information in hand.

Examples

iex> OptionParser.to_argv(foo_bar: "baz")
["--foo-bar", "baz"]
iex> OptionParser.to_argv(bool: true, bool: false, discarded: nil)
["--bool", "--no-bool"]

Some switches will output different values based on the switches types:

iex> OptionParser.to_argv([number: 2], switches: [])
["--number", "2"]
iex> OptionParser.to_argv([number: 2], switches: [number: :count])
["--number", "--number"]