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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 |
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