[Ruby] Ruby Variable Scope

Scope defines where in a program a variable is accessible. Ruby has four types of variable scope, local,global, instance and class. In addition, Ruby has one constant type. Each variable type is declared by using a special
character at the start of the variable name as outlined in the following table.

Name Begins With	Variable Scope
$	A global variable
@	An instance variable
[a-z] or _	A local variable
[A-Z]	A constant
@@	A class variable

It is useful to know, however, that a number of pre-defined global variables are available to you as a Ruby developer to obtain information about the Ruby environment. A brief summary of each of these variables is contained in the following table.

Variable Name	Variable Value
$@	The location of latest error
$_	The string last read by gets
$.	The line number last read by interpreter
$&	The string last matched by regexp
$~	The last regexp match, as an array of subexpressions
$n	The nth subexpression in the last match (same as $~[n])
$=	The case-insensitivity flag
$/	The input record separator
$\	The output record separator
$0	The name of the ruby script file currently executing
$*	The command line arguments used to invoke the script
$$	The Ruby interpreter's process ID
$?	The exit status of last executed child process