Elixir v1.9.1 OptionParser View Source

Functions for parsing command line arguments.

When calling a command, it's possible to pass command line options to modify what the command does. In this documentation, those are called "switches", in other situations they may be called "flags" or simply "options". A switch can be given a value, also called an "argument".

The main function in this module is parse/2, which parses a list of command line options and arguments into a keyword list:

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

OptionParser provides some conveniences out of the box, such as aliases and automatic handling of negation switches.

The parse_head/2 function is an alternative to parse/2 which stops parsing as soon as it finds a value that is not a switch nor a value for a previous switch.

This module also provides low-level functions, such as next/2, for parsing switches manually, as well as split/1 and to_argv/1 for parsing from and converting switches to strings.

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Functions

Low-level function that parses one option.

Parses argv into a keyword list.

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

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

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

Splits a string into argv/0 chunks.

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

Link to this section Types

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errors()

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

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

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next(argv, opts \\ [])

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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

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parse(argv, opts \\ [])

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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

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 duplicated 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:

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. This would also work:

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

Switches followed by a value will be assigned the value, as a string. Switches without an argument will be set automatically to true. 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, OptionParser will only parse switches that translate to atoms used by the runtime to avoid leaking atoms. For instance, the code below will discard the --option-parser-example switch because the :option_parser_example atom is never used anywhere:

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

However, the code below would work as long as :option_parser_example atom is used at some point later (or earlier) in the same module. For example:

{opts, _, _} = OptionParser.parse(["--option-parser-example"], switches: [debug: :boolean])
# ... then somewhere in the same module you access it ...
opts[:option_parser_example]

In other words, Elixir will 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. 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"], [], []}
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parse!(argv, opts \\ [])

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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"
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parse_head(argv, opts \\ [])

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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"], []}
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parse_head!(argv, opts \\ [])

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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"

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"]
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to_argv(enum, options \\ [])

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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 types:

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