Ruby Programming/Reference/Predefined Variables

Ruby's predefined (built-in) variables affect the behavior of the entire program, so their use in libraries isn't recommended.

The values in most predefined variables can be accessed by alternative means.

$!

• The last exception object raised. The exception object can also be accessed using => in rescue clause.

$@

• The stack backtrace for the last exception raised. The stack backtrace information can retrieved by Exception#backtrace method of the last exception.

$/

• The input record separator (newline by default). gets, readline, etc., take their input record separator as optional argument.

$\

• The output record separator (nil by default).

$,

• The output separator between the arguments to print and Array#join (nil by default). You can specify separator explicitly to Array#join.

$;

• The default separator for split (nil by default). You can specify separator explicitly for String#split.

$.

• The number of the last line read from the current input file. Equivalent to ARGF.lineno.

$<

• Synonym for ARGF.

$>

• Synonym for $defout.

$0

• The name of the current Ruby program being executed.

$$

• The process.pid of the current Ruby program being executed.

$?

• The exit status of the last process terminated.

$:

• Synonym for $LOAD_PATH.

$DEBUG

• True if the -d or --debug command-line option is specified.

$defout

• The destination output for print and printf ($stdout by default).

$F

• The variable that receives the output from split when -a is specified. This variable is set if the -a command-line option is specified along with the -p or -n option.

$FILENAME

• The name of the file currently being read from ARGF. Equivalent to ARGF.filename.

$LOAD_PATH

• An array holding the directories to be searched when loading files with the load and require methods.

$SAFE

• The security level.

    0   No checks are performed on externally supplied (tainted) data. (default)

    1   Potentially dangerous operations using tainted data are forbidden.

    2   Potentially dangerous operations on processes and files are forbidden.

    3   All newly created objects are considered tainted.

    4   Modification of global data is forbidden.

$stdin

• Standard input (STDIN by default).

$stdout

• Standard output (STDOUT by default).

$stderr

• Standard error (STDERR by default).

$VERBOSE

• True if the -v, -w, or --verbose command-line option is specified.

$- x

• The value of interpreter option -x (x=0, a, d, F, i, K, l, p, v).

The following are local variables:

$_

• The last string read by gets or readline in the current scope.

$~

• MatchData relating to the last match. Regex#match method returns the last match information.

The following variables hold values that change in accordance with the current value of $~ and can't receive assignment:

$ n ($1, $2, $3...)

• The string matched in the nth group of the last pattern match. Equivalent to m[n], where m is a MatchData object.

$&

• The string matched in the last pattern match. Equivalent to m[0], where m is a MatchData object.

$`

• The string preceding the match in the last pattern match. Equivalent to m.pre_match, where m is a MatchData object.

$'

• The string following the match in the last pattern match. Equivalent to m.post_match, where m is a MatchData object.

$+

• The string corresponding to the last successfully matched group in the last pattern match.