The region in which the private variable is recognized is called its scope. Variables declared with my are thus called lexically scoped variables.
A private variable will be recognized until the end of the innermost enclosing block, function or file. It will also be recognized in blocks contained within this region. However, a private variable of a function will not be recognized in another function called from that function (if you wish that it will, declare the variable with "local").
Lexical (private) variables will not exist and will not be recognized outside their scope.
By explicitly declaring the scope of each of your variables with my, you decrease the chance that variables from different parts of your program will accidentally have the same name and thus "step on each other". The usage of my is also important in cases that your code will be used as a modular part in other programs, whose variable names are unknown to you.
my $a; my ($a, $b, $c); #the parentheses are obligatory my @months; my %students; #a hash variable, about which we will learn later my (@months, %students);In these examples, the variables declared with my were initialized with the undef value.
You may initialize your lexical variables with other values, as in the following examples:
my $y = 2000; my @months = ("Jan", "Feb", "Apr"); my ($a, $b, $c) = @months; #the parentheses are obligatory my $text = $a . " " . $y; #some operationNote: If a list of variables is declared with my, the list must be enclosed in parentheses. If only one variable is declared with my, do not use parentheses (this might cause problems in statements like my ($line) = <FILEHANDLE>;, which we will learn later).