Programming Perl, 4th Edition

my

my TYPE EXPR : ATTRIBUTES
my EXPR : ATTRIBUTES
my TYPE EXPR
my EXPR

This operator declares one or more private variables to exist only within the innermost enclosing block, subroutine, eval, or file. If more than one variable is listed, the list must be placed in parentheses because the operator binds more tightly than commas. Only simple scalars or complete arrays and hashes may be declared this way.

The variable name cannot be package qualified, because package variables are all globally accessible through their corresponding symbol table, and lexical variables are unrelated to any symbol table. Unlike local, then, this operator has nothing to do with global variables, other than hiding any other variable of the same name from view within its scope (that is, where the private variable exists). A global variable can always be accessed through its package-qualified form, however, or through a symbolic reference.

A private variable’s scope does not start until the statement after its declaration. The variable’s scope extends into any enclosed blocks thereafter, up to the end of the scope of the variable itself.

However, this means that any subroutines you call from within the scope of a private variable cannot see the private variable unless the block that defines the subroutine itself is also textually enclosed within the scope of that variable. That sounds complicated, but it’s not once you get the hang of it. The technical term for this is lexical scoping, so we often call these ...