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* The String that is passed to the Proc depends on the

* Readline.completer_word_break_characters property. The default settings are

* that “the word under the cursor” is passed to the Proc. This is the normal

* behavior you would expect. So if you had input foo bar⇥ then only 'bar' would

* get passed to the completion Proc.

*

* Its common functionality that on a successful completion you may want to

* append a space character so that the user can immediately start working on

* their next argument. Readline has you covered. Just set

* Readline.completion_append_character.

*

* = Examples

*

* == Completion for a Static List

* require 'readline'

*

* LIST = [

* 'search', 'download', 'open',

* 'help', 'history', 'quit',

* 'url', 'next', 'clear',

* 'prev', 'past'

* ].sort

*

* comp = proc { |s| LIST.grep( /^#{Regexp.escape(s)}/ ) }

*

* Readline.completion_append_character = " "

* Readline.completion_proc = comp

*

* while line = Readline.readline('> ', true)

* p line

* end

* == Completion For Directory Contents

* require 'readline'

*

* Readline.completion_append_character = " "

* Readline.completion_proc = Proc.new do |str|

* Dir[str+'*'].grep( /^#{Regexp.escape(str)}/ )

* end

*

* while line = Readline.readline('> ', true)

* p line

* end

* = Autocompelte strategies

*

* When working with auto-complete there are some strategies that work well. To

* get some ideas you can take a look at the

* completion.rb[http://svn.ruby-lang.org/repos/ruby/trunk/lib/irb/completion.rb]

* file for irb. The common strategy is to take a list of possible strings, and

* filter it down to only those strings that start with a given substring. In

* the above examples I used Enumeration.grep and passed in a regular

* expression. Because the input comes from the user its smart to escape the

* special regular expression characters in the input using Regexp.quote or

* Regexp.escape. The source code looks like this:

* # Straightforward

* regex = Regexp.new( '^' + Regexp.escape(str) )

*

* # Shortcut using Interpolation

* regex = /^#{Regexp.escape(str)}/

* It may also be helpful to check out the abbrev library. Their description

* says it "Calculates the set of unique abbreviations for a given set of

* strings." Here is a quick example:

* require 'abbrev'

* %w[one two three].abbrev

*

* # Results in:

* # { "three"=>"three", "two"=>"two", "tw"=>"two",

* # "o"=>"one", "one"=>"one", "thre"=>"three",

* # "thr"=>"three", "th"=>"three", "on"=>"one" }

*