Pre-defined variables

$!

The exception information message set by 'raise'.

$@

Array of backtrace of the last exception thrown.

$&

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.

$~

The information about the last match in the current scope.

$=

The flag for case insensitive, nil by default.

$/

The input record separator, newline by default.

$\

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

$,

The output field separator for the print and Array#join.

$;

The default separator for String#split.

$.

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

$<

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

$>

The default output for print, 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.

$*

Command line arguments given for the script sans args.

$$

The process number of the Ruby running this script.

$?

The status of the last executed child process. This value is thread-local.

$:

Load path for scripts and binary modules by load or require.

$“

The array contains the module names loaded by require.

$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.

$LOADED_FEATURES

The alias to the $“.

$FILENAME

Current input file from $<. Same as $<.filename.

$LOAD_PATH

The alias to the $:.

$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.

$-0

The alias to $/.

$-a

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

$-d

The alias of $DEBUG. See $DEBUG above for further discussion.

$-F

The alias to $;.

$-i

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

$-I

The alias to $:.

$-l

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

$-p

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

$-v

An alias of $VERBOSE. See $VERBOSE above for further discussion.

$-w

An alias of $VERBOSE. See $VERBOSE above for further discussion.

Pre-defined global constants

TRUE

The typical true value.

FALSE

The false itself.

NIL

The nil itself.

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 alias to the $<.

ARGV

The alias to the $*.

DATA

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

RUBY_VERSION

The ruby version string (VERSION was deprecated).

RUBY_RELEASE_DATE

The release date string.

RUBY_PLATFORM

The platform identifier.