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# 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` | `$INPUT_RECORD_SEPARATOR` | Input record separator | Newline | No |
`$\` | `$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 | Reset By
--- | --- | --- | --- | --- | ---
`$0`, `$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 | English | Contains | Initially | Read-Only | Reset By
--- | --- | --- | --- | --- | ---
`$FILENAME` |  | Value returned by method `ARGF.filename` | Command-line argument or ‘-’ | Yes |
`$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 | English | Contains | Initially | Read-Only | Reset By
--- | --- | --- | --- | --- | ---
`$-F`, `$;` |  | 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`.

### `$\` (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` 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

### `$-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"