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.