OptionParser

This module contains functions to parse command line options.

Summary

Types

argv()

errors()

options()

parsed()

Functions

next(argv, opts \\ [])

Low-level function that parses one option

parse(argv, opts \\ [])

Parses argv into a keyword list

parse!(argv, opts \\ [])

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

parse_head(argv, opts \\ [])

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

parse_head!(argv, opts \\ [])

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

split(string)

Splits a string into argv/0 chunks

to_argv(enum, opts \\ [])

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

Types

argv()

argv() :: [String.t()]

errors()

errors() :: [{String.t(), String.t() | nil}]

options()

options() :: [switches: keyword(), strict: keyword(), aliases: keyword()]

parsed()

parsed() :: keyword()

Functions

next(argv, opts \\ [])

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)

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

parse(argv, opts \\ [])

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"], switches: [debug: :boolean])
{[debug: true], [], []}

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

iex> OptionParser.parse(["--source-path", "lib", "test/enum_test.exs", "--verbose"],
...>                    switches: [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 dynamic switches” section below
• :aliases - see the “Aliases” section below

Switch definitions

Switches can be specified via one of two options:

• :switches - defines some switches and their types. This function still attempts to parse switches that are not in this list.
• :strict - defines strict switches. Any switch in argv that is not specified in the list is returned in the invalid options list.

Both these options accept a keyword list of {name, type} tuples where name is an atom defining the name of the switch and type is an atom that specifies the type for the value of this switch (see the “Types” section below for the possible types and more information about type casting).

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 duplicated items 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 dynamic switches

OptionParser also includes a dynamic mode where it will attempt to parse switches dynamically. Such can be done by not specifying the :switches or :strict option.

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

Switches followed by a value will be assigned the value, as a string. Switches without an argument, like --debug in the examples above, will automatically be set to true.

Since Elixir converts switches to atoms, the dynamic mode will only parse switches that translate to atoms used by the runtime. Therefore, the code below likely won’t parse the given option since the :option_parser_example atom is never used anywhere:

OptionParser.parse(["--option-parser-example"])
# The :option_parser_example atom is not used anywhere below

However, the code below does since the :option_parser_example atom is used at some point later (or earlier) on:

{opts, _, _} = OptionParser.parse(["--option-parser-example"])
opts[:option_parser_example]

In other words, when using dynamic mode, Elixir will do the correct thing and only parse options that are used by the runtime, ignoring all others. 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. Such option is useful when you are building command-line applications that receive dynamically-named arguments but must be used with care on long-running systems.

Switches followed by a value will be assigned the value, as a string. Switches without an argument, like --debug in the examples above, will automatically be set to true.

Aliases

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

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

parse!(argv, opts \\ [])

parse!(argv(), options()) :: {parsed(), argv()} | no_return()

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"

parse_head(argv, opts \\ [])

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"], []}

parse_head!(argv, opts \\ [])

parse_head!(argv(), options()) :: {parsed(), argv()} | no_return()

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"

split(string)

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"]

to_argv(enum, opts \\ [])

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 Kernel.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 flag:

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