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. |
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