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
TRUESynonym for true.
FALSESynonym for false.
NILSynonym for nil.
ARGFAn 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 $<.
ARGVAn array containing the command-line arguments passed to the program. A synonym for $*.
DATAAn input stream for reading the lines of code following the __END__ directive. Not defined if __END__ isn't present in code.
ENVA hash-like object containing the program's environment variables. ENV can be handled as a hash.
RUBY_PLATFORMA string indicating the platform of the Ruby interpreter.
RUBY_RELEASE_DATEA string indicating the release date of the Ruby interpreter
RUBY_VERSIONA string indicating the version of the Ruby interpreter.
STDERRStandard error output stream. Default value of $stderr.
STDINStandard input stream. Default value of $stdin.
STDOUTStandard output stream. Default value of $stdout.
TOPLEVEL_BINDINGA Binding object at Ruby's top level.