Ruby Predefined Constants

The following table lists all the Ruby's Predefined Constants.

NOTE: TRUE, FALSE, and NIL are backward-compatible. It's preferable to use true, false, and nil.

Constant Name	Description
TRUE	Synonym for true.
FALSE	Synonym for false.
NIL	Synonym for nil.
ARGF	An object providing access to virtual concatenation of files passed as command-line arguments or standard input if there are no command-line arguments. A synonym for $<.
ARGV	An array containing the command-line arguments passed to the program. A synonym for $*.
DATA	An input stream for reading the lines of code following the __END__ directive. Not defined if __END__ isn't present in code.
ENV	A hash-like object containing the program's environment variables. ENV can be handled as a hash.
RUBY_PLATFORM	A string indicating the platform of the Ruby interpreter.
RUBY_RELEASE_DATE	A string indicating the release date of the Ruby interpreter
RUBY_VERSION	A string indicating the version of the Ruby interpreter.
STDERR	Standard error output stream. Default value of $stderr.
STDIN	Standard input stream. Default value of $stdin.
STDOUT	Standard output stream. Default value of $stdout.
TOPLEVEL_BINDING	A Binding object at Ruby's top level.