Perl in a Nutshell, 2nd Edition

Declarations and Scope

In Perl, only subroutines and formats require explicit declaration. Variables (and similar constructs) are automatically created when they are first assigned.

Variable declaration comes into play when you need to limit the scope of a variable’s use. You can do this in two ways:

Dynamic scoping

Creates temporary objects within a scope. Dynamically scoped constructs are visible globally, but take action only within their defined scopes. Dynamic scoping applies to variables declared with local.

Lexical scoping

Creates private constructs that are visible only within their scopes. The most frequently seen form of lexically scoped declaration is the declaration of my variables.

Therefore, we can say that a local variable is dynamically scoped, whereas a my variable is lexically scoped. Dynamically scoped variables are visible to functions called from within the block in which they are declared. Lexically scoped variables, on the other hand, are totally hidden from the outside world, including any called subroutines, unless they are declared within the same scope. See Section 4.7 later in this chapter for further discussion.