Ruby Programming/Reference/Predefined Variables

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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.