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. See
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