path: root/doc/option_params/option_params.rdoc

== Parameters for New Options

Option-creating methods in \OptionParser
accept arguments that determine the behavior of a new option:

- OptionParser#on
- OptionParser#on_head
- OptionParser#on_tail
- OptionParser#define
- OptionParser#define_head
- OptionParser#define_tail
- OptionParser#make_switch

The code examples on this page use:

- OptionParser#on, to define options.
- OptionParser#parse!, to parse the command line.
- Built-in option <tt>--help</tt>, to display defined options.

Contents:

- {Option Names}[#label-Option+Names]
  - {Short Names}[#label-Short+Names]
    - {Simple Short Names}[#label-Simple+Short+Names]
    - {Short Names with Required Arguments}[#label-Short+Names+with+Required+Arguments]
    - {Short Names with Optional Arguments}[#label-Short+Names+with+Optional+Arguments]
    - {Short Names from Range}[#label-Short+Names+from+Range]
  - {Long Names}[#label-Long+Names]
    - {Simple Long Names}[#label-Simple+Long+Names]
    - {Long Names with Required Arguments}[#label-Long+Names+with+Required+Arguments]
    - {Long Names with Optional Arguments}[#label-Long+Names+with+Optional+Arguments]
  - {Mixed Names}[#label-Mixed+Names]
- {Argument Styles}[#label-Argument+Styles]
- {Argument Values}[#label-Argument+Values]
  - {Explicit Argument Values}[#label-Explicit+Argument+Values]
    - {Explicit Values in Array}[#label-Explicit+Values+in+Array]
    - {Explicit Values in Hash}[#label-Explicit+Values+in+Hash]
  - {Argument Value Patterns}[#label-Argument+Value+Patterns]
- {Argument Converters}[#label-Argument+Converters]
  - {Date}[#label-Date]
  - {DateTime}[#label-DateTime]
  - {Time}[#label-Time]
  - {URI}[#label-URI]
  - {Shellwords}[#label-Shellwords]
  - {Integer}[#label-Integer]
  - {Float}[#label-Float]
  - {Numeric}[#label-Numeric]
  - {DecimalInteger}[#label-DecimalInteger]
  - {OctalInteger}[#label-OctalInteger]
  - {DecimalNumeric}[#label-DecimalNumeric]
  - {TrueClass}[#label-TrueClass]
  - {FalseClass}[#label-FalseClass]
  - {Object}[#label-Object]
  - {String}[#label-String]
  - {Array}[#label-Array]
  - {Regexp}[#label-Regexp]
- {Descriptions}[#label-Descriptions]
- {Handlers}[#label-Handlers]
  - {Handler Blocks}[#label-Handler+Blocks]
  - {Handler Procs}[#label-Handler+Procs]
  - {Handler Methods}[#label-Handler+Methods]
- {Terminators}[#label-Terminators]

=== Option Names

There are two kinds of option names:

- Short option name, consisting of a single hyphen and a single character.
- Long option name, consisting of two hyphens and one or more characters.

==== Short Names

===== Simple Short Names

File +short_simple.rb+ defines two options:

- One with short name <tt>-x</tt>.
- The other with two short names, in effect, aliases, <tt>-1</tt> and <tt>-%</tt>.

 :include: short_simple.rb

Executions:

  $ ruby short_simple.rb --help
  Usage: short_simple [options]
      -x                               One short name
      -1, -%                           Two short names (aliases)
  $ ruby short_simple.rb -x
  ["-x", true]
  $ ruby short_simple.rb -1 -x -%
  ["-1 or -%", true]
  ["-x", true]
  ["-1 or -%", true]

===== Short Names with Required Arguments

A short name followed (no whitespace) by a dummy word
defines an option that requires an argument.

File +short_required.rb+ defines an option <tt>-x</tt>
that requires an argument.

  :include: short_required.rb

Executions:

  $ ruby short_required.rb --help
  Usage: short_required [options]
      -xXXX                            Short name with required argument
  $ ruby short_required.rb -x
  short_required.rb:6:in `<main>': missing argument: -x (OptionParser::MissingArgument)
  $ ruby short_required.rb -x FOO
  ["-x", "FOO"]

===== Short Names with Optional Arguments

A short name followed (with whitespace) by a dummy word in square brackets
defines an option that allows an optional argument.

File +short_optional.rb+ defines an option <tt>-x</tt>
that allows an optional argument.

  :include: short_optional.rb

Executions:

  $ ruby short_optional.rb --help
  Usage: short_optional [options]
      -x [XXX]                         Short name with optional argument
  $ ruby short_optional.rb -x
  ["-x", nil]
  $ ruby short_optional.rb -x FOO
  ["-x", "FOO"]

===== Short Names from Range

You can define an option with multiple short names
taken from a range of characters.
The parser yields both the actual character cited and the value.

File +short_range.rb+ defines an option with short names
for all printable characters from <tt>!</tt> to <tt>~</tt>:

  :include: short_range.rb

Executions:

  $ ruby short_range.rb --help
  Usage: short_range [options]
      -[!-~]                           Short names in (very large) range
  $ ruby short_range.rb -!
  ["!-~", "!", nil]
  $ ruby short_range.rb -!
  ["!-~", "!", nil]
  $ ruby short_range.rb -A
  ["!-~", "A", nil]
  $ ruby short_range.rb -z
  ["!-~", "z", nil]

==== Long Names

===== Simple Long Names

File +long_simple.rb+ defines two options:

- One with long name <tt>-xxx</tt>.
- The other with two long names, in effect, aliases,
  <tt>--y1%</tt> and <tt>--z2#</tt>.

  :include: long_simple.rb

Executions:

  $ ruby long_simple.rb --help
  Usage: long_simple [options]
          --xxx                        One long name
          --y1%, --z2#                 Two long names (aliases)
  $ ruby long_simple.rb --xxx
  ["--xxx", true]
  $ ruby long_simple.rb --y1% --xxx --z2#
  ["--y1% or --z2#", true]
  ["--xxx", true]
  ["--y1% or --z2#", true]

===== Long Names with Required Arguments

A long name followed (with whitespace) by a dummy word
defines an option that requires an argument.

File +long_required.rb+ defines an option <tt>--xxx</tt>
that requires an argument.

  :include: long_required.rb

Executions:

  $ ruby long_required.rb --help
  Usage: long_required [options]
          --xxx XXX                    Long name with required argument
  $ ruby long_required.rb --xxx
  long_required.rb:6:in `<main>': missing argument: --xxx (OptionParser::MissingArgument)
  $ ruby long_required.rb --xxx FOO
  ["--xxx", "FOO"]

===== Long Names with Optional Arguments

A long name followed (with whitespace) by a dummy word in square brackets
defines an option that allows an optional argument.

File +long_optional.rb+ defines an option <tt>--xxx</tt>
that allows an optional argument.

  :include: long_optional.rb

Executions:

  $ ruby long_optional.rb --help
  Usage: long_optional [options]
          --xxx [XXX]                  Long name with optional argument
  $ ruby long_optional.rb --xxx
  ["--xxx", nil]
  $ ruby long_optional.rb --xxx FOO
  ["--xxx", "FOO"]

==== Mixed Names

An option may have both short and long names.

File +mixed_names.rb+ defines a mixture of short and long names.

  :include: mixed_names.rb

Executions:

  $ ruby mixed_names.rb --help
  Usage: mixed_names [options]
      -x, --xxx                        Short and long, simple
          --yyy                        yYYY
                                       Short and long, required argument
          --zzz                        zZZZ
                                       Short and long, optional argument
  $ ruby mixed_names.rb -x
  ["--xxx", true]
  $ ruby mixed_names.rb --xxx
  ["--xxx", true]
  $ ruby mixed_names.rb -y
  mixed_names.rb:12:in `<main>': missing argument: -y (OptionParser::MissingArgument)
  $ ruby mixed_names.rb -y FOO
  ["--yyy", "FOO"]
  $ ruby mixed_names.rb --yyy
  mixed_names.rb:12:in `<main>': missing argument: --yyy (OptionParser::MissingArgument)
  $ ruby mixed_names.rb --yyy BAR
  ["--yyy", "BAR"]
  $ ruby mixed_names.rb -z
  ["--zzz", nil]
  $ ruby mixed_names.rb -z BAZ
  ["--zzz", "BAZ"]
  $ ruby mixed_names.rb --zzz
  ["--zzz", nil]
  $ ruby mixed_names.rb --zzz BAT
  ["--zzz", "BAT"]

=== Argument Keywords

As seen above, a given option name string may itself
indicate whether the option has no argument, a required argument,
or an optional argument.

An alternative is to use a separate symbol keyword,
which is one of <tt>:NONE</tt> (the default),
<tt>:REQUIRED</tt>, <tt>:OPTIONAL</tt>.

File +argument_keywords.rb+ defines an option with a required argument.

  :include: argument_keywords.rb

Executions:

  $ ruby argument_keywords.rb --help
  Usage: argument_keywords [options]
      -x, --xxx                        Required argument
  $ ruby argument_styles.rb --xxx
  argument_styles.rb:6:in `<main>': missing argument: --xxx (OptionParser::MissingArgument)
  $ ruby argument_styles.rb --xxx FOO
  ["--xxx", "FOO"]

=== Argument Strings

Still another way to specify a required argument
is to define it in a string separate from the name string.

File +argument_strings.rb+ defines an option with a required argument.

  :include: argument_strings.rb

Executions:

  $ ruby argument_strings.rb --help
  Usage: argument_strings [options]
      -x, --xxx=XXX                    Required argument
  $ ruby argument_strings.rb --xxx
  argument_strings.rb:9:in `<main>': missing argument: --xxx (OptionParser::MissingArgument)
  $ ruby argument_strings.rb --xxx FOO
  ["--xxx", "FOO"]

=== Argument Values

Permissible argument values may be restricted
either by specifying explicit values
or by providing a pattern that the given value must match.

==== Explicit Argument Values

You can specify argument values in either of two ways:

- Specify values an array of strings.
- Specify values a hash.

===== Explicit Values in Array

You can specify explicit argument values in an array of strings.
The argument value must be one of those strings.

File +explicit_array_values.rb+ defines options with explicit argument values.

  :include: explicit_array_values.rb

Executions:

  $ ruby explicit_array_values.rb --help
  Usage: explicit_array_values [options]
      -xXXX                            Values for required argument
      -y [YYY]                         Values for optional argument
  $ ruby explicit_array_values.rb -x
  explicit_array_values.rb:9:in `<main>': missing argument: -x (OptionParser::MissingArgument)
  $ ruby explicit_array_values.rb -x foo
  ["-x", "foo"]
  $ ruby explicit_array_values.rb -x bar
  ["-x", "bar"]
  $ ruby explicit_array_values.rb -x baz
  explicit_array_values.rb:9:in `<main>': invalid argument: -x baz (OptionParser::InvalidArgument)


===== Explicit Values in Hash

You can specify explicit argument values in a hash with string keys.
The value passed must be one of those keys,
and the value yielded will be the value for that key.

File +explicit_hash_values.rb+ defines options with explicit argument values.

  :include: explicit_hash_values.rb

Executions:

  $ ruby explicit_hash_values.rb --help
  Usage: explicit_hash_values [options]
      -xXXX                            Values for required argument
      -y [YYY]                         Values for optional argument
  $ ruby explicit_hash_values.rb -x
  explicit_hash_values.rb:9:in `<main>': missing argument: -x (OptionParser::MissingArgument)
  $ ruby explicit_hash_values.rb -x foo
  ["-x", 0]
  $ ruby explicit_hash_values.rb -x bar
  ["-x", 1]
  $ ruby explicit_hash_values.rb -x baz
  explicit_hash_values.rb:9:in `<main>': invalid argument: -x baz (OptionParser::InvalidArgument)
  $ ruby explicit_hash_values.rb -y
  ["-y", nil]
  $ ruby explicit_hash_values.rb -y baz
  ["-y", 2]
  $ ruby explicit_hash_values.rb -y bat
  ["-y", 3]
  $ ruby explicit_hash_values.rb -y bam
  ["-y", nil]

==== Argument Value Patterns

You can restrict permissible argument values
by specifying a Regexp that the given argument must match.

File +matched_values.rb+ defines options with matched argument values.

  :include: matched_values.rb

Executions:

  $ ruby matched_values.rb --help
  Usage: matched_values [options]
          --xxx XXX                    Matched values
  $ ruby matched_values.rb --xxx foo
  ["--xxx", "foo"]
  $ ruby matched_values.rb --xxx FOO
  ["--xxx", "FOO"]
  $ ruby matched_values.rb --xxx bar
  matched_values.rb:6:in `<main>': invalid argument: --xxx bar (OptionParser::InvalidArgument)

=== Argument Converters

An option can specify that its argument is to be converted
from the default \String to an instance of another class.

\OptionParser has a number of built-in converters,
which are demonstrated below.

==== \Date

File +date.rb+
defines an option whose argument is to be converted to a \Date object.
The argument is converted by method
{Date.parse}[https://ruby-doc.org/stdlib/libdoc/date/rdoc/Date.html#method-c-parse].

  :include: date.rb

Executions:

  $ ruby date.rb --date 2001-02-03
  [#<Date: 2001-02-03 ((2451944j,0s,0n),+0s,2299161j)>, Date]
  $ ruby date.rb --date 20010203
  [#<Date: 2001-02-03 ((2451944j,0s,0n),+0s,2299161j)>, Date]
  $ ruby date.rb --date "3rd Feb 2001"
  [#<Date: 2001-02-03 ((2451944j,0s,0n),+0s,2299161j)>, Date]

==== \DateTime

File +datetime.rb+
defines an option whose argument is to be converted to a \DateTime object.
The argument is converted by method
{DateTime.parse}[https://ruby-doc.org/stdlib-2.6.1/libdoc/date/rdoc/DateTime.html#method-c-parse].

  :include: datetime.rb

Executions:

  $ ruby datetime.rb --datetime 2001-02-03T04:05:06+07:00
  [#<DateTime: 2001-02-03T04:05:06+07:00 ((2451943j,75906s,0n),+25200s,2299161j)>, DateTime]
  $ ruby datetime.rb --datetime 20010203T040506+0700
  [#<DateTime: 2001-02-03T04:05:06+07:00 ((2451943j,75906s,0n),+25200s,2299161j)>, DateTime]
  $ ruby datetime.rb --datetime "3rd Feb 2001 04:05:06 PM"
  [#<DateTime: 2001-02-03T16:05:06+00:00 ((2451944j,57906s,0n),+0s,2299161j)>, DateTime]

==== \Time

File +time.rb+
defines an option whose argument is to be converted to a \Time object.
The argument is converted by method
{Time.httpdate}[https://ruby-doc.org/stdlib-2.7.0/libdoc/time/rdoc/Time.html#method-c-httpdate] or
{Time.parse}[https://ruby-doc.org/stdlib-2.7.0/libdoc/time/rdoc/Time.html#method-c-parse].

  :include: time.rb

Executions:

  $ ruby time.rb --time "Thu, 06 Oct 2011 02:26:12 GMT"
  [2011-10-06 02:26:12 UTC, Time]
  $ ruby time.rb --time 2010-10-31
  [2010-10-31 00:00:00 -0500, Time]

==== \URI

File +uri.rb+
defines an option whose argument is to be converted to a \URI object.
The argument is converted by method
{URI.parse}[https://ruby-doc.org/stdlib-2.7.2/libdoc/uri/rdoc/URI.html#method-c-parse].

  :include: uri.rb

Executions:

  $ ruby uri.rb --uri https://github.com
  [#<URI::HTTPS https://github.com>, URI::HTTPS]
  $ ruby uri.rb --uri http://github.com
  [#<URI::HTTP http://github.com>, URI::HTTP]
  $ ruby uri.rb --uri file://~/var
  [#<URI::File file://~/var>, URI::File]

==== \Shellwords

File +shellwords.rb+
defines an option whose argument is to be converted to an \Array object by method
{Shellwords.shellwords}[https://ruby-doc.org/stdlib-2.7.0/libdoc/shellwords/rdoc/Shellwords.html#method-c-shellwords].

  :include: shellwords.rb

Executions:

  $ ruby shellwords.rb --shellwords "ruby my_prog.rb | less"
  [["ruby", "my_prog.rb", "|", "less"], Array]
  $ ruby shellwords.rb --shellwords "here are 'two words'"
  [["here", "are", "two words"], Array]

==== \Integer

File +integer.rb+
defines an option whose argument is to be converted to an \Integer object.
The argument is converted by method
{Kernel.Integer}[https://ruby-doc.org/core/Kernel.html#method-i-Integer].

  :include: integer.rb

Executions:

  $ ruby integer.rb --integer 100
  [100, Integer]
  $ ruby integer.rb --integer -100
  [-100, Integer]
  $ ruby integer.rb --integer 0100
  [64, Integer]
  $ ruby integer.rb --integer 0x100
  [256, Integer]
  $ ruby integer.rb --integer 0b100
  [4, Integer]

==== \Float

File +float.rb+
defines an option whose argument is to be converted to a \Float object.
The argument is converted by method
{Kernel.Float}[https://ruby-doc.org/core/Kernel.html#method-i-Float].

  :include: float.rb

Executions:

  $ ruby float.rb --float 1
  [1.0, Float]
  $ ruby float.rb --float 3.14159
  [3.14159, Float]
  $ ruby float.rb --float 1.234E2
  [123.4, Float]
  $ ruby float.rb --float 1.234E-2
  [0.01234, Float]

==== \Numeric

File +numeric.rb+
defines an option whose argument is to be converted to an instance
of \Rational, \Float, or \Integer.
The argument is converted by method
{Kernel.Rational}[https://ruby-doc.org/core/Kernel.html#method-i-Rational],
{Kernel.Float}[https://ruby-doc.org/core/Kernel.html#method-i-Float], or
{Kernel.Integer}[https://ruby-doc.org/core/Kernel.html#method-i-Integer].

  :include: numeric.rb

Executions:

  $ ruby numeric.rb --numeric 1/3
  [(1/3), Rational]
  $ ruby numeric.rb --numeric 3.333E-1
  [0.3333, Float]
  $ ruby numeric.rb --numeric 3
  [3, Integer]

==== \DecimalInteger

File +decimal_integer.rb+
defines an option whose argument is to be converted to an \Integer object.
The argument is converted by method
{Kernel.Integer}[https://ruby-doc.org/core/Kernel.html#method-i-Integer].

  :include: decimal_integer.rb

The argument may not be in a binary or hexadecimal format;
a leading zero is ignored (not parsed as octal).

Executions:

  $ ruby decimal_integer.rb --decimal_integer 100
  [100, Integer]
  $ ruby decimal_integer.rb --decimal_integer -100
  [-100, Integer]
  $ ruby decimal_integer.rb --decimal_integer 0100
  [100, Integer]
  $ ruby decimal_integer.rb --decimal_integer -0100
  [-100, Integer]

==== \OctalInteger

File +octal_integer.rb+
defines an option whose argument is to be converted to an \Integer object.
The argument is converted by method
{Kernel.Integer}[https://ruby-doc.org/core/Kernel.html#method-i-Integer].

  :include: octal_integer.rb

The argument may not be in a binary or hexadecimal format;
it is parsed as octal, regardless of whether it has a leading zero.

Executions:

  $ ruby octal_integer.rb --octal_integer 100
  [64, Integer]
  $ ruby octal_integer.rb --octal_integer -100
  [-64, Integer]
  $ ruby octal_integer.rb --octal_integer 0100
  [64, Integer]

==== \DecimalNumeric

File +decimal_numeric.rb+
defines an option whose argument is to be converted to an \Integer object.
The argument is converted by method
{Kernel.Integer}[https://ruby-doc.org/core/Kernel.html#method-i-Integer].

  :include: decimal_numeric.rb

The argument may not be in a binary or hexadecimal format;
a leading zero causes the argument to be parsed as octal.

Executions:

  $ ruby decimal_numeric.rb --decimal_numeric 100
  [100, Integer]
  $ ruby decimal_numeric.rb --decimal_numeric -100
  [-100, Integer]
  $ ruby decimal_numeric.rb --decimal_numeric 0100
  [64, Integer]

==== \TrueClass

File +true_class.rb+
defines an option whose argument is to be converted to +true+ or +false+.
The argument is evaluated by method
{Object#nil?}[https://ruby-doc.org/core-3.0.0/Object.html#method-i-nil-3F].

  :include: true_class.rb

The argument may be any of those shown in the examples below.

Executions:

  $ ruby true_class.rb --true_class true
  [true, TrueClass]
  $ ruby true_class.rb --true_class yes
  [true, TrueClass]
  $ ruby true_class.rb --true_class +
  [true, TrueClass]
  $ ruby true_class.rb --true_class false
  [false, FalseClass]
  $ ruby true_class.rb --true_class no
  [false, FalseClass]
  $ ruby true_class.rb --true_class -
  [false, FalseClass]
  $ ruby true_class.rb --true_class nil
  [false, FalseClass]

==== \FalseClass

File +false_class.rb+
defines an option whose argument is to be converted to +true+ or +false+.
The argument is evaluated by method
{Object#nil?}[https://ruby-doc.org/core-3.0.0/Object.html#method-i-nil-3F].

  :include: false_class.rb

The argument may be any of those shown in the examples below.

Executions:

  $ ruby false_class.rb --false_class false
  [false, FalseClass]
  $ ruby false_class.rb --false_class no
  [false, FalseClass]
  $ ruby false_class.rb --false_class -
  [false, FalseClass]
  $ ruby false_class.rb --false_class nil
  [false, FalseClass]
  $ ruby false_class.rb --false_class true
  [true, TrueClass]
  $ ruby false_class.rb --false_class yes
  [true, TrueClass]
  $ ruby false_class.rb --false_class +
  [true, TrueClass]

==== \Object

File +object.rb+
defines an option whose argument is not to be converted from \String.

  :include: object.rb

Executions:

  $ ruby object.rb --object foo
  ["foo", String]
  $ ruby object.rb --object nil
  ["nil", String]

==== \String

File +string.rb+
defines an option whose argument is not to be converted from \String.

  :include: string.rb

Executions:

  $ ruby string.rb --string foo
  ["foo", String]
  $ ruby string.rb --string nil
  ["nil", String]

==== \Array

File +array.rb+
defines an option whose argument is to be converted from \String
to an array of strings, based on comma-separated substrings.

  :include: array.rb

Executions:

  $ ruby array.rb --array ""
  [[], Array]
  $ ruby array.rb --array foo,bar,baz
  [["foo", "bar", "baz"], Array]
  $ ruby array.rb --array "foo, bar, baz"
  [["foo", " bar", " baz"], Array]

==== \Regexp

File +regexp.rb+
defines an option whose argument is to be converted to a \Regexp object.

  :include: regexp.rb

Executions:

  $ ruby regexp.rb --regexp foo

=== Descriptions

A description parameter is any string parameter
that is not recognized as an
{option name}[#label-Option+Names] or a
{terminator}[#label-Terminators];
in other words, it does not begin with a hypnen.

You may give any number of description parameters;
each becomes a line in the text generated by option <tt>--help</tt>.

File +descriptions.rb+ has six strings in its array +descriptions+.
These are all passed as parameters to OptionParser#on, so that they
all, line for line, become the option's description.

  :include: descriptions.rb

Executions:

  $ ruby descriptions.rb --help
  Usage: descriptions [options]
          --xxx                        Lorem ipsum dolor sit amet, consectetuer
                                       adipiscing elit. Aenean commodo ligula eget.
                                       Aenean massa. Cum sociis natoque penatibus
                                       et magnis dis parturient montes, nascetur
                                       ridiculus mus. Donec quam felis, ultricies
                                       nec, pellentesque eu, pretium quis, sem.
  $ ruby descriptions.rb --xxx
  ["--xxx", true]

=== Handlers

The handler for an option is an executable that will be called
when the option is encountered.  The handler may be:

- A block (this is most often seen).
- A proc.
- A method.

==== Handler Blocks

An option hadler may be a block.

File +block.rb+ defines an option that has a handler block.

  :include: block.rb

Executions:

  $ ruby block.rb --help
  Usage: block [options]
          --xxx                        Option with no argument
          --yyy YYY                    Option with required argument
  $ ruby block.rb --xxx
  ["Handler block for -xxx called with value:", true]
  $ ruby block.rb --yyy FOO
  ["Handler block for -yyy called with value:", "FOO"]

==== Handler Procs

An option handler may be a Proc.

File +proc.rb+ defines an option that has a handler proc.

  :include: proc.rb

Executions:

  $ ruby proc.rb --help
  Usage: proc [options]
          --xxx                        Option with no argument
          --yyy YYY                    Option with required argument
  $ ruby proc.rb --xxx
  ["Handler proc for -xxx called with value:", true]
  $ ruby proc.rb --yyy FOO
  ["Handler proc for -yyy called with value:", "FOO"]

==== Handler Methods

An option handler may be a Method.

File +proc.rb+ defines an option that has a handler method.

  :include: method.rb

Executions:

  $ ruby method.rb --help
  Usage: method [options]
          --xxx                        Option with no argument
          --yyy YYY                    Option with required argument
  $ ruby method.rb --xxx
  ["Handler method for -xxx called with value:", true]
  $ ruby method.rb --yyy FOO
  ["Handler method for -yyy called with value:", "FOO"]

=== Terminators

And finally, the terminator parameter <tt>--</tt> tells the options parser
to ignore any options farther to the right.
This can be useful if there are options not meant for the current program.

File +terminator.rb+ defines one option <tt>--my_option</tt>.

  :include: terminator.rb

The first execution fails because <tt>--nosuch</tt> is not a defined option;
the second succeeds because <tt>--</tt> causes that option to be ignored:

  $ ruby terminator.rb --my_option FOO --other_option BAR
  ["FOO", String]
  terminator.rb:6:in `<main>': invalid option: --other_option (OptionParser::InvalidOption)
  $ ruby terminator.rb --my_option FOO -- --other_option BAR
  ["FOO", String]