Programming Perl, 4th Edition

local

local EXPR

This operator does not create a local variable; use my for that. Instead, it localizes existing variables; that is, it causes one or more global variables to have locally scoped values within the innermost enclosing block, 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. All listed variables must be legal lvalues—that is, something you could assign to; this can include individual elements of arrays or hashes.

This operator works by saving the current values of the specified variables on a hidden stack and restoring them on exiting the block, subroutine, eval, or file. After the local is executed, but before the scope is exited, any subroutines and executed formats will see the local, inner value, instead of the previous, outer value, because the variable is still a global variable, despite having a localized value. The technical term for this is dynamic scoping. See the section Scoped Declarations in Chapter 4.

The EXPR may be assigned to if desired, which lets you initialize your variables as you localize them. If no initializer is given, all scalars are initialized to undef, and all arrays and hashes to (). As with ordinary assignment, if you use parentheses around the variables on the left (or if the variable is an array or hash), the expression on the right is evaluated in list context. Otherwise, the expression on the right is evaluated in scalar context.

In any event, ...