The readline library provides a pure Ruby implementation of the GNU readline C library, as well as the Readline extension that ships as part of the standard library.

require 'readline'

loop do
  line = Readline::readline('> ')
  break if line.nil? || line == 'quit'
  Readline::HISTORY.push(line)
  puts "You typed: #{line}"
end

rb-readline should work on all Unix-like systems and Windows. It is regularly used with MRI 1.8/1.9 and Rubinius. JRuby is not supported and there are no plans to support it in the future - it comes bundled with a Java implementation of Readline.

First, building the GNU readline library on MS Windows with Visual C++ is almost impossible. However, certain libraries depend on readline. By providing a pure Ruby version we eliminate the entire compiler compatibility issue.

Second, even on distributions of Windows built with MinGW (that include the readline library for Windows), the behavior was sometimes erratic and would break.

Third, even on certain Unix distributions the GNU readline library is not guaranteed to be installed. Providing a pure Ruby readline eliminates the need to install a C library first. It’s also one less link in the dependency chain, meaning we don’t need to worry about possible changes in the underlying C library affecting our interface.

Fourth, by making the interface pure Ruby, we increase the likelihood of receiving patches, feature requests, documentation updates, etc from the community at large, since not everyone knows C.

Lastly, the Readline interface that ships as part of the standard library is weak, and only provides a very limited subset of the actual GNU readline library. By providing a pure Ruby implementation we allow 3rd party library authors to write their own interface as they see fit.

For an excellent tutorial on how to use Readline in practice, please see Joseph Pecoraro’s examples at bogojoker.com/readline/.

You can also take a look at Ruby 1.9 stdlib Readline documentation located at rubydoc.info/stdlib/readline/1.9.2/frames

See Rawline for a library that began life in pure Ruby and provides an interface that’s probably more comfortable to Ruby programmer. It has certain features that Readline does not. In addition, it provides a Readline compatibility mode.

• Park Heesob (C translation, code donated as part of bounty)

• Daniel Berger (Documentation and testing)

• Luis Lavena

• Mark Somerville (Maintainer)

• Connor Atherton (Maintainer)