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https://github.com/mdub/clamp

a Ruby command-line application framework
https://github.com/mdub/clamp

command-line command-line-parser ruby

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a Ruby command-line application framework

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# Clamp



[![Gem Version](https://badge.fury.io/rb/clamp.png)](http://badge.fury.io/rb/clamp)

[![Build Status](https://secure.travis-ci.org/mdub/clamp.png?branch=master)](http://travis-ci.org/mdub/clamp)



"Clamp" is a minimal framework for command-line utilities.



It handles boring stuff like parsing the command-line, and generating help, so you can get on with making your command actually do stuff.



## Not another one!



Yeah, sorry.  There are a bunch of existing command-line parsing libraries out there, and Clamp draws inspiration from a variety of sources, including [Thor], [optparse], and [Clip].  In the end, though, I wanted a slightly rounder wheel.  (Although, Clamp has a _lot_ in common with Ara T. Howard's [main.rb]. Had I been aware of that project at the time, I might not have written Clamp.)



[optparse]: http://ruby-doc.org/stdlib/libdoc/optparse/rdoc/index.html

[Thor]: http://github.com/wycats/thor

[Clip]: http://clip.rubyforge.org/

[main.rb]: https://github.com/ahoward/main



## Quick Start



A typical Clamp script looks like this:



```ruby

require 'clamp'



Clamp do



  option "--loud", :flag, "say it loud"

  option ["-n", "--iterations"], "N", "say it N times", default: 1 do |s|

    Integer(s)

  end



  parameter "WORDS ...", "the thing to say", attribute_name: :words



  def execute

    the_truth = words.join(" ")

    the_truth.upcase! if loud?

    iterations.times do

      puts the_truth

    end

  end



end

```



Internally, Clamp models a command as a Ruby class (a subclass of `Clamp::Command`), and a command execution as an instance of that class.  The example above is really just syntax-sugar for:



```ruby

require 'clamp'



class SpeakCommand < Clamp::Command



  option "--loud", :flag, "say it loud"

  option ["-n", "--iterations"], "N", "say it N times", default: 1 do |s|

    Integer(s)

  end



  parameter "WORDS ...", "the thing to say", attribute_name: :words



  def execute

    the_truth = words.join(" ")

    the_truth.upcase! if loud?

    iterations.times do

      puts the_truth

    end

  end



end



SpeakCommand.run

```



Class-level methods like `option` and `parameter` declare attributes, in a similar way to `attr_accessor`, and arrange for them to be populated automatically based on command-line arguments.  They are also used to generate `help` documentation.



There are more examples demonstrating various features of Clamp [on Github][examples].



[examples]: https://github.com/mdub/clamp/tree/master/examples



## Declaring options



Options are declared using the `option` method.  The three required arguments are:



  1. the option switch (or switches),

  2. an option argument name

  3. a short description



For example:



```ruby

option "--flavour", "FLAVOUR", "ice-cream flavour"

```



It works a little like `attr_accessor`, defining reader and writer methods on the command class.  The attribute name is inferred from the switch (in this case, "`flavour`").  When you pass options to your command, Clamp will populate the attributes, which are then available for use in your `#execute` method.



```ruby

def execute

  puts "You chose #{flavour}.  Excellent choice!"

end

```



If you don't like the inferred attribute name, you can override it:



```ruby

option "--type", "TYPE", "type of widget", attribute_name: :widget_type

                                           # to avoid clobbering Object#type

```



### Short/long option switches



The first argument to `option` can be an array, rather than a single string, in which case all the switches are treated as aliases:



```ruby

option ["-s", "--subject"], "SUBJECT", "email subject line"

```



### Flag options



Some options are just boolean flags.  Pass "`:flag`" as the second parameter to tell Clamp not to expect an option argument:



```ruby

option "--verbose", :flag, "be chatty"

```



For flag options, Clamp appends "`?`" to the generated reader method; ie. you get a method called "`#verbose?`", rather than just "`#verbose`".



Negatable flags are easy to generate, too:



```ruby

option "--[no-]force", :flag, "be forceful (or not)"

```



Clamp will handle both "`--force`" and "`--no-force`" options, setting the value of "`#force?`" appropriately.



### Required options



Although "required option" is an oxymoron, Clamp lets you mark an option as required, and will verify that a value is provided:



```ruby

option "--password", "PASSWORD", "the secret password", required: true

```



Note that it makes no sense to mark a `:flag` option, or one with a `:default`, as `:required`.



### Multivalued options



Declaring an option "`:multivalued`" allows it to be specified multiple times on the command line.



```ruby

option "--format", "FORMAT", "output format", multivalued: true

```



The underlying attribute becomes an Array, and the suffix "`_list`" is appended to the default attribute name.  In this case, an attribute called "`format_list`" would be generated (unless you override the default by specifying an `:attribute_name`).



### Hidden options



Declaring an option "`:hidden`" will cause it to be hidden from `--help` output.



```ruby

option "--some-option", "VALUE", "Just a little option", hidden: true

```



### Version option



A common idiom is to have an option `--version` that outputs the command version and doesn't run any subcommands.  This can be achieved by:



```ruby

option "--version", :flag, "Show version" do

  puts MyGem::VERSION

  exit(0)

end

```



## Declaring parameters



Positional parameters can be declared using `parameter`, specifying



  1. the parameter name, and

  2. a short description



For example:



```ruby

parameter "SRC", "source file"

```



Like options, parameters are implemented as attributes of the command, with the default attribute name derived from the parameter name (in this case, "`src`"). By convention, parameter names are specified in uppercase, to make them obvious in usage help.



### Optional parameters



Wrapping a parameter name in square brackets indicates that it's optional, e.g.



```ruby

parameter "[TARGET_DIR]", "target directory"

```



### Multivalued (aka "greedy") parameters



Three dots at the end of a parameter name makes it "greedy" - it will consume all remaining command-line arguments.  For example:



```ruby

parameter "FILE ...", "input files", attribute_name: :files

```



Like multivalued options, greedy parameters are backed by an Array attribute (named with a "`_list`" suffix, by default).



## Parsing and validation of options and parameters



When you `#run` a command, it will first attempt to `#parse` command-line arguments, and map them onto the declared options and parameters, before invoking your `#execute` method.



Clamp will verify that all required (ie. non-optional) parameters are present, and signal a error if they aren't.



### Validation



Both `option` and `parameter` accept an optional block.  If present, the block will be

called with the raw string argument, and is expected to validate it.  The value returned by the block will be assigned to the underlying attribute, so it's also a good place to coerce the String to a different type, if appropriate.



For example:



```ruby

option "--port", "PORT", "port to listen on" do |s|

  Integer(s)

end

```



If the block raises an ArgumentError, Clamp will catch it, and report that the value was bad:



```ruby

!!!plain

ERROR: option '--port': invalid value for Integer: "blah"

```



For multivalued options and parameters, the validation block will be called for each value specified.



More complex validation, e.g. those involving multiple options/parameters, should be performed within the `#execute` method.  Use `#signal_usage_error` to tell the user what they did wrong, e.g.



```ruby

def execute

  if port < 1024 && user != 'root'

    signal_usage_error "port restricted for non-root users"

  end

  # ... carry on ...

end

```



### Advanced option/parameter handling



While Clamp provides an attribute-writer method for each declared option or parameter, you always have the option of overriding it to provide custom argument-handling logic, e.g.



```ruby

parameter "SERVER", "location of server"



def server=(server)

  @server_address, @server_port = server.split(":")

end

```



### Default values



Default values can be specified for options, and optional parameters:



```ruby

option "--flavour", "FLAVOUR", "ice-cream flavour", default: "chocolate"



parameter "[HOST]", "server host", default: "localhost"

```



For more advanced cases, you can also specify default values by defining a method called "`default_#{attribute_name}`":



```ruby

option "--http-port", "PORT", "web-server port", default:  9000



option "--admin-port", "PORT", "admin port"



def default_admin_port

   http_port + 1

end

```



### Environment variable support



Options (and optional parameters) can also be associated with environment variables:



```ruby

option "--port", "PORT", "the port to listen on", environment_variable: "MYAPP_PORT" do |val|

  val.to_i

end



parameter "[HOST]", "server address", environment_variable: "MYAPP_HOST"

```



Clamp will check the specified envariables in the absence of values supplied on the command line, before looking for a default value.



### Allowing options after parameters



By default, Clamp only recognises options _before_ positional parameters.



Some other option-parsing libraries - notably [GNU `getopt(3)`](https://www.gnu.org/software/libc/manual/html_node/Using-Getopt.html) - allow option and parameter arguments to appear in any order on the command-line, e.g.



    foobar --foo=bar something --fnord=snuffle another-thing



If you want Clamp to allow options and parameters to be "interspersed" in this way, set:



```ruby

Clamp.allow_options_after_parameters = true

```



## Declaring Subcommands



Subcommand support helps you wrap a number of related commands into a single script (ala tools like "`git`").  Clamp will inspect the first command-line argument (after options are parsed), and delegate to the named subcommand.



Unsuprisingly, subcommands are declared using the `subcommand` method. e.g.



```ruby

Clamp do



  subcommand "init", "Initialize the repository" do



    def execute

      # ...

    end



  end



end

```



Clamp generates an anonymous subclass of the current class, to represent the subcommand.  Alternatively, you can provide an explicit subcommand class:



```ruby

class MainCommand < Clamp::Command



  subcommand "init", "Initialize the repository", InitCommand



end



class InitCommand < Clamp::Command



  def execute

    # ...

  end



end

```



Like options, subcommands may have aliases:



```ruby

Clamp do



  subcommand ["initialize", "init"], "Initialize the repository" do

    # ...

  end



end

```



### Default subcommand



You can set a default subcommand, at the class level, as follows:



```ruby

Clamp do



  self.default_subcommand = "status"



  subcommand "status", "Display current status" do



    def execute

      # ...

    end



  end



end

```



Then, if when no SUBCOMMAND argument is provided, the default will be selected.



### Subcommand options and parameters



Options are inheritable, so any options declared for a command are supported by it's sub-classes (e.g. those created using the block form of `subcommand`).  Parameters, on the other hand, are not inherited - each subcommand must declare it's own parameter list.



Note that, if a subcommand accepts options, they must be specified on the command-line _after_ the subcommand name.



You can define a `subcommand_missing` method that is called when user tries to run an unknown subcommand:



```ruby

Clamp do

  def subcommand_missing(name)

    if name == "foo"

      return Object.const_get(:FooPlugin) if Object.const_defined?(:FooPlugin)

      abort "Subcommand 'foo' requires plugin X"

    end

  end

end

```



## Getting help



All Clamp commands support a "`--help`" option, which outputs brief usage documentation, based on those seemingly useless extra parameters that you had to pass to `option` and `parameter`.



```sh

$ speak --help

Usage:

    speak [OPTIONS] WORDS ...



Arguments:

    WORDS ...                     the thing to say



Options:

    --loud                        say it loud

    -n, --iterations N            say it N times (default: 1)

    -h, --help                    print help

```



## Localization



Clamp comes with support for overriding strings with custom translations. You can use localization library of your choice and override the strings at startup.



Example usage:



```ruby

require 'gettext'



Clamp.messages = {

  too_many_arguments:        _("too many arguments"),

  option_required:           _("option '%s' is required"),

  option_or_env_required:    _("option '%s' (or env %s) is required"),

  option_argument_error:     _("option '%s': %s")

  # ...

}

```



See [messages.rb](https://github.com/mdub/clamp/blob/master/lib/clamp/messages.rb) for full list of available messages.



## License



Copyright (C) 2011 [Mike Williams](mailto:[email protected])



Permission is hereby granted, free of charge, to any person obtaining a copy

of this software and associated documentation files (the "Software"), to

deal in the Software without restriction, including without limitation the

rights to use, copy, modify, merge, publish, distribute, sublicense, and/or

sell copies of the Software, and to permit persons to whom the Software is

furnished to do so, subject to the following conditions:



The above copyright notice and this permission notice shall be included in

all copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER

IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN

CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.



## Contributing to Clamp



Source-code for Clamp is [on Github](https://github.com/mdub/clamp).