View Source OptionParser (Elixir v1.12.2)
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.
Link to this section Summary
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
Link to this section Functions
@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 optionkey
withvalue
was successfully parsed{:invalid, key, value, rest}
- the optionkey
is invalid withvalue
(returned when the value cannot be parsed according to the switch type){:undefined, key, value, rest}
- the optionkey
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 givenargv
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 whilevalue
is the value for that switch parsed according toopts
(see the "Examples" section for more information)args
is a list of the remaining arguments inargv
as stringsinvalid
is a list of invalid options as{option_name, value}
whereoption_name
is the raw option andvalue
isnil
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 inargv
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 totrue
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
. Specifyingswitch_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"], [], []}
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 inparse/2
)rest
is the list of arguments (same as inparse/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"
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"], []}
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 inparse_head/2
)rest
is the list of arguments (same as inparse_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"]
@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 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"]