Predefined Variables

Predefined variable	Description
`$!`	The exception information message containing the last exception raised. `raise` sets this variable. Access with `=>` in a `rescue` clause.
`$@`	The stack backtrace of the last exception, retrievable via `Exception#backtrace`.
`$&`	The string matched by the last successful pattern match in this scope, or `nil` if the last pattern match failed. Same as `m[0]` where `m` is a `MatchData` object. Read only. Local.
`$'`	String preceding whatever was matched by the last successful pattern match in the current scope, or `nil` if the last pattern match failed. Same as `m.pre_match` where `m` is a `MatchData` object. Read only. Local.
`$'`	String following whatever was matched by the last successful pattern match in the current scope, or `nil` if the last pattern match failed. Same as `m.post_match` where `m` is a `MatchData` object. Read only. Local.
`$+`	Last bracket matched by the last successful search pattern, or `nil` if the last pattern match failed. Useful if you don't know which of a set of alternative patterns matched. Read only. Local.
`$1, $2 . . .`	Subpattern from the corresponding set of parentheses in the last successful pattern matched, not counting patterns matched in nested blocks that have been exited already, or `nil` if the last pattern match failed. Same as `m[n]` where `m` is a `MatchData` object. Read only. Local.
`$˜`	Information about the last match in the current scope. `Regex#match` returns the last match information. Setting this variable affects match variables like `$&`, `$+`, `$1`, `$2`, etc. The nth subexpression can be retrieved by `$˜[nth]`. Local.
`$=`	Case-insensitive flag; `nil` by default.
`$/`	Input record separator, newline by default. Works like awk's RS variable. If it is set to `nil`, a whole file will be read at once. `gets`, `readline`, etc. take the input record separator as an optional argument.
`$\`	Output record separator for print and `IO#write`; `nil` by default.
`$,`	Output field separator between arguments; also the default separator for `Array#join`, which allows you to indicate a separator explicitly.
`$;`	The default separator for `String#split`; `nil` by default.
`$.`	The current input line number of the last file that was read. Same as `ARGF.lineno`.
`$<`	The virtual concatenation file of the files given by command-line arguments, or standard input (in case no argument file is supplied). $<.`filename` returns the current filename. Synonym for `ARGF`.
`$>`	Default output for print, `printf`, `$stdout` by default. Synonym for `$defout`.
`$_`	Last input line of string by `gets` or `readline` in the current scope; set to `nil` if `gets` or `readline` meets EOF. Local.
`$0`	Name of the current Ruby program being executed.
`$*`	Command-line arguments given for the script. The options for the Ruby interpreter are already removed.
`$$`	Process number (`process.pid`) of the Ruby program being executed.
`$?`	Exit status of the last executed process.
`$:`	Synonym for `$LOAD_PATH`.
`$"`	Array containing the module names loaded by `require`. Used for prevent `require` from loading modules twice.
`$DEBUG`	True if `-d` or `--debug` switch is set.
`$defout`	Default output for `print`, `printf`; `$stdout` by default. Synonym for `$>`.
`$F`	Receives output from `split` when `-a` specified. Set if `-a` is set along with `-p` and `-n`.
`$FILENAME`	Name of the file currently being read from `ARGF`. Same as `ARGF.``filename` or `$<.``filename`.
`$LOAD_PATH`	Synonym for `$:`.
`$SAFE`	Security level: 0 No checks on externally supplied (tainted) date. Default. 1 Potentially dangerous operations using tainted data are forbidden. 2 Potentially dangerous operations performed on processes and files are forbidden. 3 All newly created objects are considered tainted. 4 Modification of global data is forbidden.
`$stdin`	The current standard input; `STDIN` by default.
`$stdout`	The current standard output; `STDOUT` by default.
`$stderr`	The current standard error output; `STDERR` by default.
`$VERBOSE`	True if `verbose` flag is set by the `-v`, `-w`, or `--verbose` switch of the Ruby interpreter.
`$-0`	Alias of `$/`.
`$-a`	True if option `-a` is set. Read-only.
`$-d`	Alias of `$DEBUG`.
`$-F`	Alias of `$;`.
`$-i`	In in-place-edit mode, holds the extension, otherwise `nil`. Can enable or disable in-place-edit mode.
`$-I`	Alias of `$:`.
`$-l`	True if option `-lis` set. Read-only.
`$-p`	True if option `-pis` set. Read-only.