Pre-defined global variables

$!

The Exception object set by Kernel#raise.

$@

The same as $!.backtrace.

$~

The information about the last match in the current scope (thread-local and frame-local).

$&

The string matched by the last successful match.

$`

The string to the left of the last successful match.

$'

The string to the right of the last successful match.

$+

The highest group matched by the last successful match.

$1

The Nth group of the last successful match. May be > 1.

$=

This variable is no longer effective. Deprecated.

$/

The input record separator, newline by default. Aliased to $-0.

$\

The output record separator for Kernel#print and IO#write. Default is nil.

$,

The output field separator for Kernel#print and Array#join. Non-nil $, will be deprecated.

$;

The default separator for String#split. Non-nil $; will be deprecated. Aliased to $-F.

$.

The current input line number of the last file that was read.

$<

The same as ARGF.

$>

The default output stream for Kernel#print and Kernel#printf. $stdout by default.

$_

The last input line of string by gets or readline.

$0

Contains the name of the script being executed. May be assignable.

$*

The same as ARGV.

$$

The process number of the Ruby running this script. Same as Process.pid.

$?

The status of the last executed child process (thread-local).

$LOAD_PATH

Load path for searching Ruby scripts and extension libraries used by Kernel#load and Kernel#require. Aliased to $: and $-I. Has a singleton method $LOAD_PATH.resolve_feature_path(feature) that returns [:rb or :so, path], which resolves the feature to the path the original Kernel#require method would load.

$LOADED_FEATURES

The array contains the module names loaded by require. Aliased to $“.

$DEBUG

The debug flag, which is set by the -d switch. Enabling debug output prints each exception raised to $stderr (but not its backtrace). Setting this to a true value enables debug output as if -d were given on the command line. Setting this to a false value disables debug output. Aliased to $-d.

$FILENAME

Current input filename from ARGF. Same as ARGF.filename.

$stderr

The current standard error output.

$stdin

The current standard input.

$stdout

The current standard output.

$VERBOSE

The verbose flag, which is set by the -w or -v switch. Setting this to a true value enables warnings as if -w or -v were given on the command line. Setting this to nil disables warnings, including from Kernel#warn. Aliased to $-v and $-w.

$-a

True if option -a is set. Read-only variable.

$-i

In in-place-edit mode, this variable holds the extension, otherwise nil.

$-l

True if option -l is set. Read-only variable.

$-p

True if option -p is set. Read-only variable.

Pre-defined global constants

TRUE

The typical true value. Deprecated.

FALSE

The false itself. Deprecated.

NIL

The nil itself. Deprecated.

STDIN

The standard input. The default value for $stdin.

STDOUT

The standard output. The default value for $stdout.

STDERR

The standard error output. The default value for $stderr.

ENV

The hash contains current environment variables.

ARGF

The virtual concatenation of the files given on command line (or from $stdin if no files were given).

ARGV

An Array of command line arguments given for the script.

DATA

The file object of the script, pointing just after __END__.

TOPLEVEL_BINDING

The Binding of the top level scope.

RUBY_VERSION

The Ruby language version.

RUBY_RELEASE_DATE

The release date string.

RUBY_PLATFORM

The platform identifier.

RUBY_PATCHLEVEL

The patchlevel for this ruby. If this is a development build of ruby the patchlevel will be -1.

RUBY_REVISION

The GIT commit hash for this ruby.

RUBY_COPYRIGHT

The copyright string for ruby.

RUBY_ENGINE

The name of the Ruby implementation.

RUBY_ENGINE_VERSION

The version of the Ruby implementation.

RUBY_DESCRIPTION

The same as ruby --version, a String describing various aspects of the Ruby implementation.