Ruby预定义全局变量
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.
$0The 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.
$DEBUGTrue if the -d or --debug command-line option is specified.
$defoutThe destination output for print and printf ($stdout by default).
$FThe 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.
$FILENAMEThe name of the file currently being read from ARGF. Equivalent to ARGF.filename.
$LOAD_PATHAn array holding the directories to be searched when loading files with the load and require methods.
$SAFEThe security level. See?
