Pre-Defined Global Variables

Some of the pre-defined global variables have synonyms that are available via module English. For each of those, the English synonym is given.

To use the module:

require 'English'

In Brief

Exceptions

Variable	English	Contains	Initially	Read-Only	Reset By
`$!`	`$ERROR_INFO`	Exception object or `nil`	`nil`	Yes	Kernel.raise
`$@`	`$ERROR_POSITION`	Array of backtrace positions or `nil`	`nil`	Yes	Kernel.raise

Matched Data

Variable	English	Contains	Initially	Read-Only	Reset By
`$~`	`$LAST_MATCH_INFO`	MatchData object or `nil`	`nil`	No	Matcher methods
`$&`	`$MATCH`	Matched substring or `nil`	`nil`	No	Matcher methods
$`	`$PRE_MATCH`	Substring left of match or `nil`	`nil`	No	Matcher methods
`$'`	`$POST_MATCH`	Substring right of match or `nil`	`nil`	No	Matcher methods
`$+`	`$LAST_PAREN_MATCH`	Last group matched or `nil`	`nil`	No	Matcher methods
`$1`		First group matched or `nil`	`nil`	Yes	Matcher methods
`$2`		Second group matched or `nil`	`nil`	Yes	Matcher methods
`$n`		nth group matched or `nil`	`nil`	Yes	Matcher methods

Separators

Variable	English	Contains	Initially	Read-Only	Reset By
`$/`, `$-0`	`$INPUT_RECORD_SEPARATOR`	Input record separator	Newline	No
`$</code>`	`$OUTPUT_RECORD_SEPARATOR`	Output record separator	{nil}	No

Streams

Variable	English	Contains	Initially	Read-Only	Reset By
`$stdin`		Standard input stream	{STDIN}	No
`$stdout`		Standard output stream	{STDOUT}	No
`$stderr`		Standard error stream	{STDERR}	No
`$<`	`$DEFAULT_INPUT`	Default standard input	{ARGF}	Yes
`$>`	`$DEFAULT_OUTPUT`	Default standard output	{STDOUT}	No
`$.`	`$INPUT_LINE_NUMBER`, `$NR`	Input position of most recently read stream	0	No	Certain read methods
`$_`	`$LAST_READ_LINE`	String from most recently read stream	{nil}	No	Certain read methods

Processes

Variable	English	Contains	Initially	Read-Only
`$0`, `$PROGRAM_NAME`		Program name	Program name	No
`$*`	`$ARGV`	ARGV array	{ARGV}	Yes
`$$`	`$PROCESS_ID`, `$PID`	Process id	Process PID	Yes
`$?`	`$CHILD_STATUS`	Status of recently exited child	{nil}	Yes
`$LOAD_PATH`, `$:`, `$-I`		Array of search paths	Ruby defaults	Yes
`$LOADED_FEATURES`, `$"`		Array of load paths	Ruby defaults	Yes

Debugging

Variable	Contains	Initially	Read-Only
`$FILENAME`	Value returned by method {ARGF.filename}	Command-line argument or '-'	Yes
`$DEBUG`	Whether option `-d` or `--debug` was given	Command-line option	No
`$VERBOSE`	Whether option `-V` or `-W` was given	Command-line option	No

Other Variables

Variable	Contains	Read-Only
`$-F`, `$;`	Separator given with command-line option `-F`
`$-a`	Whether option `-a` was given	Yes
`$-i`	Extension given with command-line option `-i`	No
`$-l`	Whether option `-l` was given	Yes
`$-p`	Whether option `-p` was given	Yes
`$F`	Array of `$_` split by `$-F`

Exceptions

`$!` (Exception)

Contains the Exception object set by {Kernel.raise}:

begin
  raise RuntimeError.new('Boo!')
rescue RuntimeError
  p $!
end

Output:

{#<}RuntimeError: Boo!>

English - $ERROR_INFO

`$@` (Backtrace)

Same as $!.backtrace; returns an array of backtrace positions:

begin
  raise RuntimeError.new('Boo!')
rescue RuntimeError
  pp $@.take(4)
end

Output:

["(irb):338:in `<top (required)>'",
 "/snap/ruby/317/lib/ruby/3.2.0/irb/workspace.rb:119:in `eval'",
 "/snap/ruby/317/lib/ruby/3.2.0/irb/workspace.rb:119:in `evaluate'",
 "/snap/ruby/317/lib/ruby/3.2.0/irb/context.rb:502:in `evaluate'"]

English - $ERROR_POSITION.

Matched Data

These global variables store information about the most recent successful match in the current scope.

For details and examples, see Regexp Global Variables.

`$~` (MatchData)

MatchData object created from the match; thread-local and frame-local.

English - $LAST_MATCH_INFO.

`$&` (Matched Substring)

The matched string.

English - $MATCH.

$` (Pre-Match Substring)

The string to the left of the match.

English - $PREMATCH.

`$'` (Post-Match Substring)

The string to the right of the match.

English - $POSTMATCH.

`$+` (Last Matched Group)

The last group matched.

English - $LAST_PAREN_MATCH.

`$1`, `$2`, Etc. (Matched Group)

For $n the nth group of the match.

No English.

Separators

`$/` (Input Record Separator)

An input record separator, initially newline. Set by the [command-line option -0].

Setting to non-nil value by other than the command-line option is deprecated.

English - $INPUT_RECORD_SEPARATOR, $RS.

Aliased as $-0.

`$</code> (Output Record Separator)`


An output record separator, initially {nil}.
Copied from $/ when the [command-line option -l] is
given.
Setting to non-nil value by other than the command-line option is
deprecated.
English - $OUTPUT_RECORD_SEPARATOR, $ORS.
Streams
$stdin (Standard Input)
The current standard input stream; initially:
$stdin # => #<IO:<STDIN>>
$stdout (Standard Output)
The current standard output stream; initially:
$stdout # => #<IO:<STDOUT>>
$stderr (Standard Error)
The current standard error stream; initially:
$stderr # => #<IO:<STDERR>>
$< (ARGF or $stdin)
Points to stream ARGF if not empty, else to stream $stdin; read-only.
English - $DEFAULT_INPUT.
$> (Default Standard Output)
An output stream, initially $stdout.
English - $DEFAULT_OUTPUT
$. (Input Position)
The input position (line number) in the most recently read stream.
English - $INPUT_LINE_NUMBER, $NR
$_ (Last Read Line)
The line (string) from the most recently read stream.
English - $LAST_READ_LINE.
Processes
$0
Initially, contains the name of the script being executed;
may be reassigned.
$* (ARGV)
Points to ARGV.
English - $ARGV.
$$ (Process ID)
The process ID of the current process. Same as {Process.pid}.
English - $PROCESS_ID, $PID.
$? (Child Status)
Initially {nil}, otherwise the {Process::Status} object
created for the most-recently exited child process;
thread-local.
English - $CHILD_STATUS.
$LOAD_PATH (Load Path)
Contains the array of paths to be searched
by {Kernel.load} and {Kernel.require}.
Singleton method $LOAD_PATH.resolve_feature_path(feature)
returns:

[:rb, path], where {path} is the path to the Ruby file to be
loaded for the given feature.
[:so, path], where {path} is the path to the shared object file
to be loaded for the given feature.
{nil} if there is no such {feature} and {path}.

Examples:
$LOAD_PATH.resolve_feature_path('timeout')
# => [:rb, "/snap/ruby/317/lib/ruby/3.2.0/timeout.rb"]
$LOAD_PATH.resolve_feature_path('date_core')
# => [:so, "/snap/ruby/317/lib/ruby/3.2.0/x86_64-linux/date_core.so"]
$LOAD_PATH.resolve_feature_path('foo')
# => nil
Aliased as $: and $-I.
$LOADED_FEATURES
Contains an array of the paths to the loaded files:
$LOADED_FEATURES.take(10)
# =>
["enumerator.so",
 "thread.rb",
 "fiber.so",
 "rational.so",
 "complex.so",
 "ruby2_keywords.rb",
 "/snap/ruby/317/lib/ruby/3.2.0/x86_64-linux/enc/encdb.so",
 "/snap/ruby/317/lib/ruby/3.2.0/x86_64-linux/enc/trans/transdb.so",
 "/snap/ruby/317/lib/ruby/3.2.0/x86_64-linux/rbconfig.rb",
 "/snap/ruby/317/lib/ruby/3.2.0/rubygems/compatibility.rb"]
Aliased as $".
Debugging
$FILENAME
The value returned by method {ARGF.filename}.
$DEBUG
Initially {true} if [command-line option -d] or
[--debug][command-line option -d] is given, otherwise initially {false};
may be set to either value in the running program.
When {true}, prints each raised exception to $stderr.
Aliased as $-d.
$VERBOSE
Initially {true} if [command-line option -v] or
[command-line option -w] is given, otherwise initially {false};
may be set to either value, or to {nil}, in the running program.
When {true}, enables Ruby warnings.
When {nil}, disables warnings, including those from {Kernel.warn}.
Aliased as $-v and $-w.
Other Variables
$-F
The default field separator in {String#split;} must be a String or a
Regexp, and can be set with [command-line option -F].
Setting to non-nil value by other than the command-line option is
deprecated.
Aliased as $;.
$-a
Whether [command-line option -a] was given; read-only.
$-i
Contains the extension given with [command-line option -i],
or {nil} if none.
An alias of {ARGF.inplace_mode}.
$-l
Whether [command-line option -l] was set; read-only.
$-p
Whether [command-line option -p] was given; read-only.
$F
If the [command-line option -a] is given, the array
obtained by splitting $_ by $-F is assigned at the start of each
-l/-p loop.
Deprecated
$=
$,
Pre-Defined Global Constants
Summary
Streams



Constant
Contains




{STDIN}
Standard input stream.


{STDOUT}
Standard output stream.


{STDERR}
Standard error stream.



Environment



Constant
Contains




{ENV}
Hash of current environment variable names and values.


{ARGF}
String concatenation of files given on the command line, or $stdin if none.


{ARGV}
Array of the given command-line arguments.


{TOPLEVEL_BINDING}
Binding of the top level scope.


{RUBY_VERSION}
String Ruby version.


{RUBY_RELEASE_DATE}
String Ruby release date.


{RUBY_PLATFORM}
String Ruby platform.


{RUBY_PATCH_LEVEL}
String Ruby patch level.


{RUBY_REVISION}
String Ruby revision.


{RUBY_COPYRIGHT}
String Ruby copyright.


{RUBY_ENGINE}
String Ruby engine.


{RUBY_ENGINE_VERSION}
String Ruby engine version.


{RUBY_DESCRIPTION}
String Ruby description.



Embedded Data



Constant
Contains




{DATA}
File containing embedded data (lines following {__END__}, if any).



Streams
{STDIN}
The standard input stream (the default value for $stdin):
STDIN # => #<IO:<STDIN>>
{STDOUT}
The standard output stream (the default value for $stdout):
STDOUT # => #<IO:<STDOUT>>
{STDERR}
The standard error stream (the default value for $stderr):
STDERR # => #<IO:<STDERR>>
Environment
{ENV}
A hash of the contains current environment variables names and values:
ENV.take(5)
# =>
[["COLORTERM", "truecolor"],
 ["DBUS_SESSION_BUS_ADDRESS", "unix:path=/run/user/1000/bus"],
 ["DESKTOP_SESSION", "ubuntu"],
 ["DISPLAY", ":0"],
 ["GDMSESSION", "ubuntu"]]
{ARGF}
The virtual concatenation of the files given on the command line, or from
$stdin if no files were given, "-" is given, or after
all files have been read.
{ARGV}
An array of the given command-line arguments.
{TOPLEVEL_BINDING}
The Binding of the top level scope:
TOPLEVEL_BINDING # => #<Binding:0x00007f58da0da7c0>
{RUBY_VERSION}
The Ruby version:
RUBY_VERSION # => "3.2.2"
{RUBY_RELEASE_DATE}
The release date string:
RUBY_RELEASE_DATE # => "2023-03-30"
{RUBY_PLATFORM}
The platform identifier:
RUBY_PLATFORM # => "x86_64-linux"
{RUBY_PATCHLEVEL}
The integer patch level for this Ruby:
RUBY_PATCHLEVEL # => 53
For a development build the patch level will be -1.
{RUBY_REVISION}
The git commit hash for this Ruby:
RUBY_REVISION # => "e51014f9c05aa65cbf203442d37fef7c12390015"
{RUBY_COPYRIGHT}
The copyright string:
RUBY_COPYRIGHT
# => "ruby - Copyright (C) 1993-2023 Yukihiro Matsumoto"
{RUBY_ENGINE}
The name of the Ruby implementation:
RUBY_ENGINE # => "ruby"
{RUBY_ENGINE_VERSION}
The version of the Ruby implementation:
RUBY_ENGINE_VERSION # => "3.2.2"
{RUBY_DESCRIPTION}
The description of the Ruby implementation:
RUBY_DESCRIPTION
# => "ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]"
Embedded Data
{DATA}
Defined if and only if the program has this line:
__END__
When defined, {DATA} is a File object
containing the lines following the {__END__},
positioned at the first of those lines:
p DATA
DATA.each_line { |line| p line }
__END__

Output:
{#<}File:t.rb>
"Foo\n"
"Bar\n"
"Baz\n"

Constant	Contains
{STDIN}	Standard input stream.
{STDOUT}	Standard output stream.
{STDERR}	Standard error stream.

Constant	Contains
{ENV}	Hash of current environment variable names and values.
{ARGF}	String concatenation of files given on the command line, or `$stdin` if none.
{ARGV}	Array of the given command-line arguments.
{TOPLEVEL_BINDING}	Binding of the top level scope.
{RUBY_VERSION}	String Ruby version.
{RUBY_RELEASE_DATE}	String Ruby release date.
{RUBY_PLATFORM}	String Ruby platform.
{RUBY_PATCH_LEVEL}	String Ruby patch level.
{RUBY_REVISION}	String Ruby revision.
{RUBY_COPYRIGHT}	String Ruby copyright.
{RUBY_ENGINE}	String Ruby engine.
{RUBY_ENGINE_VERSION}	String Ruby engine version.
{RUBY_DESCRIPTION}	String Ruby description.

Pre-Defined Global Variables

In Brief

Exceptions

Matched Data

Separators

Streams

Processes

Debugging

Other Variables

Exceptions

$! (Exception)

$@ (Backtrace)

Matched Data

$~ (MatchData)

$& (Matched Substring)

$` (Pre-Match Substring)

$' (Post-Match Substring)

$+ (Last Matched Group)

$1, $2, Etc. (Matched Group)

Separators

$/ (Input Record Separator)

$</code> (Output Record Separator)

Streams

$stdin (Standard Input)

$stdout (Standard Output)

$stderr (Standard Error)

$< (ARGF or $stdin)

$> (Default Standard Output)

$. (Input Position)

$_ (Last Read Line)

Processes

$0

$* (ARGV)

$$ (Process ID)

$? (Child Status)

$LOAD_PATH (Load Path)

$LOADED_FEATURES

Debugging

$FILENAME

$DEBUG

$VERBOSE

Other Variables

$-F

$-a

$-i

$-l

$-p

$F

Deprecated

$=

$,

Pre-Defined Global Constants

Summary

Streams

Environment

Embedded Data

Streams

{STDIN}

{STDOUT}

{STDERR}

Environment

{ENV}

{ARGF}

{ARGV}

{TOPLEVEL_BINDING}

{RUBY_VERSION}

{RUBY_RELEASE_DATE}

{RUBY_PLATFORM}

{RUBY_PATCHLEVEL}

{RUBY_REVISION}

{RUBY_COPYRIGHT}

{RUBY_ENGINE}

{RUBY_ENGINE_VERSION}

{RUBY_DESCRIPTION}

Embedded Data

{DATA}

`$!` (Exception)

`$@` (Backtrace)

`$~` (MatchData)

`$&` (Matched Substring)

`$'` (Post-Match Substring)

`$+` (Last Matched Group)

`$1`, `$2`, Etc. (Matched Group)

`$/` (Input Record Separator)

`$</code> (Output Record Separator)`

`$stdin` (Standard Input)

`$stdout` (Standard Output)

`$stderr` (Standard Error)

`$<` (ARGF or $stdin)

`$>` (Default Standard Output)

`$.` (Input Position)

`$_` (Last Read Line)

`$0`

`$*` (ARGV)

`$$` (Process ID)

`$?` (Child Status)

`$LOAD_PATH` (Load Path)

`$LOADED_FEATURES`

`$FILENAME`

`$DEBUG`

`$VERBOSE`

`$-F`

`$-a`

`$-i`

`$-l`

`$-p`

`$F`

`$=`

`$,`