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'

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.

Pattern Matching

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.

English - $INPUT_RECORD_SEPARATOR, $RS.

Aliased as $-0.

`$\` (Output Record Separator)

An output record separator, initially nil.

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 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 -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 $-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. Deprecated $= $, $; Pre-Defined Global Constants 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"

Pre-Defined Global Variables

Exceptions

$! (Exception)

$@ (Backtrace)

Pattern Matching

$~ (MatchData)

$& (Matched Substring)

$` (Pre-Match Substring)

$' (Post-Match Substring)

$+ (Last Matched Group)

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

Separators

$/ (Input Record Separator)

$\ (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

$-a

$-i

$-l

$-p

Deprecated

$=

$,

$;

Pre-Defined Global Constants

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)

`$\` (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`

`$-a`

`$-i`

`$-l`

`$-p`

`$=`

`$,`

`$;`