Variables in Ruby

Variables and other identifiers normally start with an alphabetic letter or a special modifier. The basic rules are as follows:

• Local variables (and pseudovariables such as self and nil) begin with a lowercase letter or an underscore.
• Global variables begin with a $ (dollar sign).
• Instance variables (within an object) begin with an @ (at sign).
• Class variables (within a class) begin with two @ signs.
• Constants begin with capital letters.
• For purposes of forming identifiers, the underscore (_) may be used as a lowercase letter.
• Special variables starting with a dollar sign (such as $1 and $/) are not dealt with here.

Here are some examples of each of these:

• Local variables alpha, _ident, some_var
• Pseudovariables self, nil, __FILE__
• Constants K6chip, Length, LENGTH
• Instance variables @foobar, @thx1138, @NOT_CONST
• Class variable @@phydeaux, @@my_var, @@NOT_CONST
• Global variables $beta, $B12vitamin, $NOT_CONST

There are no declarations of variables in Ruby. It is good practice, however, to assign nil to a variable initially. This certainly does not assign a type to the variable and does not truly initialize it, but it does inform the parser that this is a variable name rather than a method name.