opt_parse_builder

A Ruby Gem for processing CLI arguments using optparse. Adds to optparse a compact builder-style DSL, operand (positional argument) parsing, and easy sharing of argument definitions within a suite of commands.

Features:

• A compact, simple builder style DSL

• Composability - Arguments can be defined separately from their use, allowing common arguments to be shared shared within a suite of programs.

• Operand parsing - Adds parsing of operands) (aka positional arguments)

• Builds on solid ground - Uses tried and true OptParse.

• Familiarity - Arguments to OptParse#on are passed through with very little change, so you don't have to learn a new syntax for defining options.

• Not a framework - This library provides only improved argument parsing. There is no base class for your program to inherit from, no module for it to include, and no imposed structure.

• No magic, no surprises - Plain and explicit.

• Cohesion - Everything about an argument is defined in one place. You don't have to define the argument's help text in one place, the default value in another, etc.

• Narrow API - Simple and easy to use.

• Fully documented - Includes full code documentation and examples.

• Stable API - Uses semantic versioning. Promises not to break your program without incrementing the major version number.

• Programmed simply - Easy to understand and modify.

• Fully tested - Extensive unit test suite.

Hello, World

It is valuable to provide a simple example which can be modified and expanded upon:

require "opt_parse_builder"

arg_parser = OptParseBuilder.build_parser do |args|
  args.banner "A simple example"
  args.add do |arg|
    arg.key :path
    arg.required_operand
  end
  args.add do |arg|
    arg.key :verbose
    arg.on "-v", "--verbose", "Be verbose"
  end
  args.separator "Some explanatory text at the bottom"
end

arg_values = arg_parser.parse!
p arg_values.verbose
p arg_values.path

Installation

Add this line to your application's Gemfile:

gem 'opt_parse_builder'

And then execute:

$ bundle

Or install it yourself as:

$ gem install opt_parse_builder

Explanation of some features

Builder style DSL

You build an argument parser using a builder style DSL, like this:

arg_parser = OptParseBuilder.build_parser do |args|
  args.add do |arg|
    arg.key :verbose
    arg.on "-v", "--verbose", "Be verbose"
  end
end

Once built, a parser is normally used like this:

arg_values = arg_parser.parse!

and argument values retrieved using struct or hash notation:

p arg_values.verbose
p arg_values[:verbose]

Composability

An argument definition can be created separately from its use:

VERBOSE = OptParseBuilder.build_argument do |arg|
  arg.key :verbose
  arg.on "-v", "--verbose", "Print extra output"
end

parser = OptParseBuilder.build_parser do |args|
  args.add VERBOSE
end

Use in program suites

This is especially useful where a suite of programs share some arguments in common. Instead of defining common arguments over and over, you can define them once and then reuse them in each program.

Design note This is the reason this library was created. Other solutions I found for sharing common CLI options required the programs to be part of a framework; I wanted something that worked by itself.

# common_arguments.rb

require "opt_parse_builder"

module CommonArguments
  VERBOSE = OptParseBuilder.build_argument do |arg|
    arg.key :verbose
    arg.on "-v", "--verbose", "Print extra output"
  end
end

# read_input.rb

require_relative "common_arguments"

ARG_PARSER = OptParseBuilder.build_parser do |args|
  args.banner "Read and store the input data"
  args.add do |arg|
    arg.key 
    arg.required_operand
  end
  args.add CommonArguments::VERBOSE
end

# write_report.rb

require_relative "common_arguments"

ARG_PARSER = OptParseBuilder.build_parser do |args|
  args.banner "Print a report based on data previously read"
  args.add CommonArguments::VERBOSE
  args.add do |arg|
    arg.key :detail
    arg.on "-d", "--detail", "Add the detail section to the report"
  end
end

Switching between required and optional

When adding a pre-built operand to a parser, you can change change it from required to optional:

PATH = OptParseBuilder.build_argument do |arg|
  arg.key :path
  arg.required_operand
end

ARG_PARSER = OptParser.build_parser do |args|
  args.add PATH.optional
end

or from optional to required:

PATH = OptParseBuilder.build_argument do |arg|
  arg.key :path
  arg.optional_operand
end

ARG_PARSER = OptParser.build_parser do |args|
  args.add PATH.required
end

Argument Building Examples

Most of these examples use a shorthand where the surrounding code is not shown:

arg.key = :foo
arg.on "-f"

With the surrounding code, that would be this:

parser = OptparserBuilder.new do |args|
  args.add do |arg|
    arg.key = :foo
    arg.on = "-f"
  end
end

or this:

arg = OptParseBuilder.build_argument do |arg|
  arg.key = :foo
  arg.on = "-f"
end

Null argument

A null argument, having no value or visible effect:

OptParseBuilder.build_argument do |arg|
end

This has little value to you, but it fell out of the design for free, and it is useful in the implementation.

Banner only

An argument with only banner text (but see OptParseBuilder#banner for the usual way to do this). "Banner" is how OptParse describes text that appears at the top of the --help output.

OptParseBuilder.build_argument do |arg|
  arg.banner "Some banner text"
  arg.banner "A second line of banner text"
  arg.banner <<~BANNER
    A third line
    A fourth line
  BANNER
end

Applicable builder methods:

• banner

Banner text can be added to any argument.

Separator only

An argument with only separator text (but see OptParseBuilder#banner for the usual way to do this). "Separator" is how OptParse describes text that appears at the bottom of the --help output.

OptParseBuilder.build_argument do |arg|
  arg.serparator "Separator text"
  arg.serparator "A second line of separator text"
  arg.serparator <<~SERPARATOR
    A third line
    A fourth line
  SERPARATOR
end

Applicable builder methods:

• separator

Separator text can be added to any argument.

Constant value

An argument with a constant value.

OptParseBuilder.build_argument do |arg|
  arg.key :limit
  arg.default 12345
end

Applicable builder methods:

• key
• default
• banner (optional)
• separator (optional)

This is of limited value, but it fell out of the design for free.

Simple option

A simple option parsed by OptParse:

OptParseBuilder.build_argument do |arg|
  arg.key :quiet
  arg.on "-q", "--quiet", "Suppress normal output"
end

Applicable builder methods:

• key
• on
• default (optional)
• handler (optional)
• banner (optional)
• separator (optional)

Option with value

A value option parsed by OptParse:

OptParseBuilder.build_argument do |arg|
  arg.key :iterations
  arg.default 100
  arg.on "-i", "--iterations=N",
  arg.on "Number of iterations (default _DEFAULT_)"
end

The string "DEFAULT" is replaced with the default value (in this example, "100").

Applicable builder methods:

• key
• on
• default (optional)
• handler (optional)
• banner (optional)
• separator (optional)

Required Operand

A required operand consumes one argument, with an error if there isn't one to consume.

This example overrides the help name, which is used to describe the operand in the --help text. Optional and splat arguments can also have a help name override.

OptParseBuilder.build_argument do |arg|
  arg.key :group
  arg.required_operand help_name: "resource group"
  arg.optional_operand
end

Applicable builder methods:

• key
• required_operand
• default (optional)
• banner (optional)
• separator (optional)

Optional operand

An optional operand consumes one argument. If there isn't an argument to consume, then the value is either nil (if no default was specified), or the specified default value.

OptParseBuilder.build_argument do |arg|
  arg.key :group_name
  arg.default "main"
  arg.optional_operand
end

Applicable builder methods:

• key
• optional_operand
• default (optional)
• banner (optional)
• separator (optional)

Splat Operand

A "splat" operand consumes all remaining arguments. Its value is always an array.

OptParseBuilder.build_argument do |arg|
  arg.key :input_path
  arg.optional_operand
end

Applicable builder methods:

• key
• splat_operand
• default (optional)
• banner (optional)
• separator (optional)

Error handling and abnormal termination

The invokation of help via "-h" or "--help" prints out the program help and ends the program with exitcode 0.

Errors during building result in an uncaught BuildError.

OptParse errors are handled by Kernel#abort, which prints the error to $stderr and ends the program with exit code 1.

Ruby versions supported

• 2.5
• 2.6
• 2.7
• 3.0

Versioning

This library uses semantic versioning. As long as you stick to the public API, upgrades to this library will not break your program without incrementing the major version number.

The public API is that document using RDOC comments. If a class or method is documented with # :nodoc:, then it's not part of the public API.

Development

After checking out the repo, run bundle to install dependencies. Then run rake test to run the tests.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/wconrad/opt_parse_builder.

Terminology

These terms are used in this library's code and documentation:

• Argument - An option or operand; a single element of ARGV

• Option - An argument parsed by optparse, like -v or --size=12

• Switch - An option that is either present or not, like -v

• Value option - An option with a value, like --size=12

• Operand - An argument not parsed by optparse, like /path/to/my/file. Also called a "positional argument."

• Required operand - An operand that must be present or an error results.

• Optional operand - An operand that may be present or not; if not present, it receives either nil or a default that you set.

• Splat operand - An operand that consumes all remaining operands, resulting in an array (possibly empty) of strings.