File: Tutorial — optparse Ruby-3.3.6 p108

Tutorial

Why `OptionParser`?

When a Ruby program executes, it captures its command-line arguments and options into variable ARGV. This simple program just prints its ARGV:

:include: ruby/argv.rb

Execution, with arguments and options:

$ ruby argv.rb foo --bar --baz bat bam
["foo", "--bar", "--baz", "bat", "bam"]

The executing program is responsible for parsing and handling the command-line options.

OptionParser offers methods for parsing and handling those options.

With OptionParser, you can define options so that for each option:

The code that defines the option and code that handles that option are in the same place.
The option may take no argument, a required argument, or an optional argument.
The argument may be automatically converted to a specified class.
The argument may be restricted to specified forms.
The argument may be restricted to specified values.

The class also has method #help, which displays automatically-generated help text.

To Begin With
Defining Options
Option Names
Option Arguments
Argument Values
- Explicit Argument Values
  - Explicit Values in Array
  - Explicit Values in Hash
- Argument Value Patterns
Keyword Argument into
Argument Converters
Help
Top List and Base List
Methods for Defining Options
Parsing

To Begin With

To use OptionParser:

Require the OptionParser code.
Create an OptionParser object.
Define one or more options.
Parse the command line.

File basic.rb defines three options, -x, -y, and -z, each with a descriptive string, and each with a block.

:include: ruby/basic.rb

From these defined options, the parser automatically builds help text:

$ ruby basic.rb --help
Usage: basic [options]
    -x                               Whether to X
    -y                               Whether to Y
    -z                               Whether to Z

When an option is found during parsing, the block defined for the option is called with the argument value. An invalid option raises an exception.

Method #parse!, which is used most often in this tutorial, removes from ARGV the options and arguments it finds, leaving other non-option arguments for the program to handle on its own. The method returns the possibly-reduced ARGV array.

Executions:

$ ruby basic.rb -x -z
["x", true]
["z", true]
[]
$ ruby basic.rb -z -y -x
["z", true]
["y", true]
["x", true]
[]
$ ruby basic.rb -x input_file.txt output_file.txt
["x", true]
["input_file.txt", "output_file.txt"]
$ ruby basic.rb -a
basic.rb:16:in `<main>': invalid option: -a (OptionParser::InvalidOption)

Defining Options

A common way to define an option in OptionParser is with instance method OptionParser#on.

The method may be called with any number of arguments (whose order does not matter), and may also have a trailing optional keyword argument into.

The given arguments determine the characteristics of the new option. These may include:

One or more short option names.
One or more long option names.
Whether the option takes no argument, an optional argument, or a required argument.
Acceptable forms for the argument.
Acceptable values for the argument.
A proc or method to be called when the parser encounters the option.
String descriptions for the option.

Option Names

You can give an option one or more names of two types:

Short (1-character) name, beginning with one hyphen (-).
Long (multi-character) name, beginning with two hyphens (--).

Short Option Names

A short option name consists of a hyphen and a single character.

File short_names.rb defines an option with a short name, -x, and an option with two short names (aliases, in effect) -y and -z.

:include: ruby/short_names.rb

Executions:

$ ruby short_names.rb --help
Usage: short_names [options]
    -x                               Short name
    -1, -%                           Two short names
$ ruby short_names.rb -x
["x", true]
$ ruby short_names.rb -1
["-1 or -%", true]
$ ruby short_names.rb -%
["-1 or -%", true]

Multiple short names can “share” a hyphen:

$ ruby short_names.rb -x1%
["x", true]
["-1 or -%", true]
["-1 or -%", true]

Long Option Names

A long option name consists of two hyphens and a one or more characters (usually two or more characters).

File long_names.rb defines an option with a long name, --xxx, and an option with two long names (aliases, in effect) --y1% and --z2#.

:include: ruby/long_names.rb

Executions:

$ ruby long_names.rb --help
Usage: long_names [options]
        --xxx                        Long name
        --y1%, --z2#                 Two long names
$ ruby long_names.rb --xxx
["-xxx", true]
$ ruby long_names.rb --y1%
["--y1% or --z2#", true]
$ ruby long_names.rb --z2#
["--y1% or --z2#", true]

A long name may be defined with both positive and negative senses.

File long_with_negation.rb defines an option that has both senses.

:include: ruby/long_with_negation.rb

Executions:

$ ruby long_with_negation.rb --help
Usage: long_with_negation [options]
        --[no-]binary                Long name with negation
$ ruby long_with_negation.rb --binary
[true, TrueClass]
$ ruby long_with_negation.rb --no-binary
[false, FalseClass]

Mixing Option Names

Many developers like to mix short and long option names, so that a short name is in effect an abbreviation of a long name.

File mixed_names.rb defines options that each have both a short and a long name.

:include: ruby/mixed_names.rb

Executions:

$ ruby mixed_names.rb --help
Usage: mixed_names [options]
    -x, --xxx                        Short and long, no argument
    -y, --yyyYYY                     Short and long, required argument
    -z, --zzz [ZZZ]                  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"]

Option Name Abbreviations

By default, abbreviated option names on the command-line are allowed. An abbreviated name is valid if it is unique among abbreviated option names.

:include: ruby/name_abbrev.rb

Executions:

$ ruby name_abbrev.rb --help
Usage: name_abbrev [options]
    -n, --dry-run
    -d, --draft
$ ruby name_abbrev.rb -n
["--dry-run", true]
$ ruby name_abbrev.rb --dry-run
["--dry-run", true]
$ ruby name_abbrev.rb -d
["--draft", true]
$ ruby name_abbrev.rb --draft
["--draft", true]
$ ruby name_abbrev.rb --d
name_abbrev.rb:9:in `<main>': ambiguous option: --d (OptionParser::AmbiguousOption)
$ ruby name_abbrev.rb --dr
name_abbrev.rb:9:in `<main>': ambiguous option: --dr (OptionParser::AmbiguousOption)
$ ruby name_abbrev.rb --dry
["--dry-run", true]
$ ruby name_abbrev.rb --dra
["--draft", true]

You can disable abbreviation using method require_exact.

:include: ruby/no_abbreviation.rb

Executions:

$ ruby no_abbreviation.rb --dry-ru
no_abbreviation.rb:10:in `<main>': invalid option: --dry-ru (OptionParser::InvalidOption)
$ ruby no_abbreviation.rb --dry-run
["--dry-run", true]

Option Arguments

An option may take no argument, a required argument, or an optional argument.

Option with No Argument

All the examples above define options with no argument.

Option with Required Argument

Specify a required argument for an option by adding a dummy word to its name definition.

File required_argument.rb defines two options; each has a required argument because the name definition has a following dummy word.

:include: ruby/required_argument.rb

When an option is found, the given argument is yielded.

Executions:

$ ruby required_argument.rb --help
Usage: required_argument [options]
    -x, --xxx XXX                    Required argument via short name
    -y, --y YYY                      Required argument via long name
$ ruby required_argument.rb -x AAA
["--xxx", "AAA"]
$ ruby required_argument.rb -y BBB
["--yyy", "BBB"]

Omitting a required argument raises an error:

$ ruby required_argument.rb -x
required_argument.rb:9:in `<main>': missing argument: -x (OptionParser::MissingArgument)

Option with Optional Argument

Specify an optional argument for an option by adding a dummy word enclosed in square brackets to its name definition.

File optional_argument.rb defines two options; each has an optional argument because the name definition has a following dummy word in square brackets.

:include: ruby/optional_argument.rb

When an option with an argument is found, the given argument yielded.

Executions:

$ ruby optional_argument.rb --help
Usage: optional_argument [options]
    -x, --xxx [XXX]                  Optional argument via short  name
    -y, --yyy [YYY]                  Optional argument via long name
$ ruby optional_argument.rb -x AAA
["--xxx", "AAA"]
$ ruby optional_argument.rb -y BBB
["--yyy", "BBB"]

Omitting an optional argument does not raise an error.

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, or an unambiguous abbreviation.

File explicit_array_values.rb defines options with explicit argument values.

:include: ruby/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 f
["-x", "foo"]
$ ruby explicit_array_values.rb -x bar
["-x", "bar"]
$ ruby explicit_array_values.rb -y ba
explicit_array_values.rb:9:in `<main>': ambiguous argument: -y ba (OptionParser::AmbiguousArgument)
$ 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, or an unambiguous abbreviation; the value yielded will be the value for that key.

File explicit_hash_values.rb defines options with explicit argument values.

:include: ruby/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 f
["-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 ba
explicit_hash_values.rb:9:in `<main>': ambiguous argument: -y ba (OptionParser::AmbiguousArgument)
$ 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: ruby/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)

Keyword Argument `into`

In parsing options, you can add keyword option into with a hash-like argument; each parsed option will be added as a name/value pair.

This is useful for:

Collecting options.
Checking for missing options.
Providing default values for options.

Collecting Options

Use keyword argument into to collect options.

:include: ruby/collected_options.rb

Executions:

$ ruby collected_options.rb --help
Usage: into [options]
    -x, --xxx                        Short and long, no argument
    -y, --yyyYYY                     Short and long, required argument
    -z, --zzz [ZZZ]                  Short and long, optional argument
$ ruby collected_options.rb --xxx
{:xxx=>true}
$ ruby collected_options.rb --xxx --yyy FOO
{:xxx=>true, :yyy=>"FOO"}
$ ruby collected_options.rb --xxx --yyy FOO --zzz Bar
{:xxx=>true, :yyy=>"FOO", :zzz=>"Bar"}
$ ruby collected_options.rb --xxx --yyy FOO --yyy BAR
{:xxx=>true, :yyy=>"BAR"}

Note in the last execution that the argument value for option --yyy was overwritten.

Checking for Missing Options

Use the collected options to check for missing options.

:include: ruby/missing_options.rb

Executions:

$ ruby missing_options.rb --help
Usage: missing_options [options]
    -x, --xxx                        Short and long, no argument
    -y, --yyyYYY                     Short and long, required argument
    -z, --zzz [ZZZ]                  Short and long, optional argument
$ ruby missing_options.rb --yyy FOO
missing_options.rb:11:in `<main>': Missing required options: [:xxx, :zzz] (RuntimeError)

Default Values for Options

Initialize the into argument to define default values for options.

:include: ruby/default_values.rb

Executions:

$ ruby default_values.rb --help
Usage: default_values [options]
    -x, --xxx                        Short and long, no argument
    -y, --yyyYYY                     Short and long, required argument
    -z, --zzz [ZZZ]                  Short and long, optional argument
$ ruby default_values.rb --yyy FOO
{:yyy=>"FOO", :zzz=>"BBB"}

Argument Converters

An option can specify that its argument is to be converted from the default String to an instance of another class. There are a number of built-in converters.

Example: File date.rb defines an option whose argument is to be converted to a Date object. The argument is converted by method Date#parse.

:include: ruby/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]

You can also define custom converters. See Argument Converters for both built-in and custom converters.

Help

OptionParser makes automatically generated help text available.

The help text consists of:

A banner, showing the usage.
Option short and long names.
Option dummy argument names.
Option descriptions.

Example code:

:include: ruby/help.rb

The option names and dummy argument names are defined as described above.

The option description consists of the strings that are not themselves option names; An option can have more than one description string. Execution:

Usage: help [options]
    -x, --xxx                        Adipiscing elit. Aenean commodo ligula eget.
                                     Aenean massa. Cum sociis natoque penatibus
    -y, --yyy YYY                    Lorem ipsum dolor sit amet, consectetuer.
    -z, --zzz [ZZZ]                  Et magnis dis parturient montes, nascetur
                                     ridiculus mus. Donec quam felis, ultricies
                                     nec, pellentesque eu, pretium quis, sem.

The program name is included in the default banner: Usage: #{program_name} [options]; you can change the program name.

:include: ruby/help_program_name.rb

Execution:

$ ruby help_program_name.rb --help
Usage: help_program_name.rb [options]

You can also change the entire banner.

:include: ruby/help_banner.rb

Execution:

$ ruby help_banner.rb --help
Usage: ruby help_banner.rb

By default, the option names are indented 4 spaces and the width of the option-names field is 32 spaces.

You can change these values, along with the banner, by passing parameters to OptionParser.new.

:include: ruby/help_format.rb

Execution:

$ ruby help_format.rb --help
ruby help_format.rb [options]
  -x, --xxx            Adipiscing elit. Aenean commodo ligula eget.
                       Aenean massa. Cum sociis natoque penatibus
  -y, --yyy YYY        Lorem ipsum dolor sit amet, consectetuer.
  -z, --zzz [ZZZ]      Et magnis dis parturient montes, nascetur
                       ridiculus mus. Donec quam felis, ultricies
                       nec, pellentesque eu, pretium quis, sem.

Top List and Base List

An OptionParser object maintains a stack of ::OptionParser::List objects, each of which has a collection of zero or more options. It is unlikely that you’ll need to add or take away from that stack.

The stack includes:

The top list, given by OptionParser#top.
The base list, given by OptionParser#base.

When OptionParser builds its help text, the options in the top list precede those in the base list.

Methods for Defining Options

Option-defining methods allow you to create an option, and also append/prepend it to the top list or append it to the base list.

Each of these next three methods accepts a sequence of parameter arguments and a block, creates an option object using method OptionParser#make_switch (see below), and returns the created option:

Method OptionParser#define appends the created option to the top list.
Method OptionParser#define_head prepends the created option to the top list.
Method OptionParser#define_tail appends the created option to the base list.

These next three methods are identical to the three above, except for their return values:

Method OptionParser#on is identical to method OptionParser#define, except that it returns the parser object self.
Method OptionParser#on_head is identical to method OptionParser#define_head, except that it returns the parser object self.
Method OptionParser#on_tail is identical to method OptionParser#define_tail, except that it returns the parser object self.

Though you may never need to call it directly, here’s the core method for defining an option:

Method OptionParser#make_switch accepts an array of parameters and a block. See Parameters for New Options. This method is unlike others here in that it:
- Accepts an array of parameters; others accept a sequence of parameter arguments.
- Returns an array containing the created option object, option names, and other values; others return either the created option object or the parser object self.

Parsing

OptionParser has six instance methods for parsing.

Three have names ending with a “bang” (!):

parse!
order!
permute!

Each of these methods:

Accepts an optional array of string arguments argv; if not given, argv defaults to the value of OptionParser#default_argv, whose initial value is ARGV.
Accepts an optional keyword argument into (see Keyword Argument into).
Returns argv, possibly with some elements removed.

The three other methods have names not ending with a “bang”:

parse
order
permute

Each of these methods:

Accepts an array of string arguments or zero or more string arguments.
Accepts an optional keyword argument into and its value into. (see Keyword Argument into).
Returns argv, possibly with some elements removed.

Method `parse!`

Method parse!:

Accepts an optional array of string arguments argv; if not given, argv defaults to the value of OptionParser#default_argv, whose initial value is ARGV.
Accepts an optional keyword argument into (see Keyword Argument into).
Returns argv, possibly with some elements removed.

The method processes the elements in argv beginning at argv[0], and ending, by default, at the end.

Otherwise processing ends and the method returns when:

The terminator argument -- is found; the terminator argument is removed before the return.
Environment variable POSIXLY_CORRECT is defined and a non-option argument is found; the non-option argument is not removed. Note that the value of that variable does not matter, as only its existence is checked.

File parse_bang.rb:

:include: ruby/parse_bang.rb

Help:

$ ruby parse_bang.rb --help
Usage: parse_bang [options]
        --xxx
        --yyy YYY
        --zzz [ZZZ]

Default behavior:

$ ruby parse_bang.rb input_file.txt output_file.txt --xxx --yyy FOO --zzz BAR
["--xxx", true]
["--yyy", "FOO"]
["--zzz", "BAR"]
Returned: ["input_file.txt", "output_file.txt"] (Array)

Processing ended by terminator argument:

$ ruby parse_bang.rb input_file.txt output_file.txt --xxx --yyy FOO -- --zzz BAR
["--xxx", true]
["--yyy", "FOO"]
Returned: ["input_file.txt", "output_file.txt", "--zzz", "BAR"] (Array)

Processing ended by non-option found when POSIXLY_CORRECT is defined:

$ POSIXLY_CORRECT=true ruby parse_bang.rb --xxx input_file.txt output_file.txt -yyy FOO
["--xxx", true]
Returned: ["input_file.txt", "output_file.txt", "-yyy", "FOO"] (Array)

Method `parse`

Method parse:

Accepts an array of string arguments or zero or more string arguments.
Accepts an optional keyword argument into and its value into. (see Keyword Argument into).
Returns argv, possibly with some elements removed.

If given an array ary, the method forms array argv as ary.dup. If given zero or more string arguments, those arguments are formed into array argv.

The method calls

parse!(argv, into: into)

Note that environment variable POSIXLY_CORRECT and the terminator argument -- are honored.

File parse.rb:

:include: ruby/parse.rb

Help:

$ ruby parse.rb --help
Usage: parse [options]
        --xxx
        --yyy YYY
        --zzz [ZZZ]

Default behavior:

$ ruby parse.rb input_file.txt output_file.txt --xxx --yyy FOO --zzz BAR
["--xxx", true]
["--yyy", "FOO"]
["--zzz", "BAR"]
Returned: ["input_file.txt", "output_file.txt"] (Array)

Processing ended by terminator argument:

$ ruby parse.rb input_file.txt output_file.txt --xxx --yyy FOO -- --zzz BAR
["--xxx", true]
["--yyy", "FOO"]
Returned: ["input_file.txt", "output_file.txt", "--zzz", "BAR"] (Array)

Processing ended by non-option found when POSIXLY_CORRECT is defined:

$ POSIXLY_CORRECT=true ruby parse.rb --xxx input_file.txt output_file.txt -yyy FOO
["--xxx", true]
Returned: ["input_file.txt", "output_file.txt", "-yyy", "FOO"] (Array)

Method `order!`

Calling method OptionParser#order! gives exactly the same result as calling method OptionParser#parse! with environment variable POSIXLY_CORRECT defined.

Method `order`

Calling method OptionParser#order gives exactly the same result as calling method OptionParser#parse with environment variable POSIXLY_CORRECT defined.

Method `permute!`

Calling method OptionParser#permute! gives exactly the same result as calling method OptionParser#parse! with environment variable POSIXLY_CORRECT not defined.

Method `permute`

Calling method OptionParser#permute gives exactly the same result as calling method OptionParser#parse with environment variable POSIXLY_CORRECT not defined.

Tutorial

Why OptionParser?

Contents

To Begin With

Defining Options

Option Names

Short Option Names

Long Option Names

Mixing Option Names

Option Name Abbreviations

Option Arguments

Option with No Argument

Option with Required Argument

Option with Optional Argument

Argument Values

Explicit Argument Values

Explicit Values in Array

Explicit Values in Hash

Argument Value Patterns

Keyword Argument into

Collecting Options

Checking for Missing Options

Default Values for Options

Argument Converters

Help

Top List and Base List

Methods for Defining Options

Parsing

Method parse!

Method parse

Method order!

Method order

Method permute!

Method permute

Why `OptionParser`?

Keyword Argument `into`

Method `parse!`

Method `parse`

Method `order!`

Method `order`

Method `permute!`

Method `permute`