ruby--ruby/ext/readline

The Readline module provides interface for GNU Readline.
This module defines a number of methods to facilitate completion
and accesses input history from the Ruby interpreter.
This module supported Edit Line(libedit) too.
libedit is compatible with GNU Readline.

GNU Readline:: http://www.gnu.org/directory/readline.html
libedit::      http://www.thrysoee.dk/editline/

See RDoc for Readline module.