In Perl, you can use the logical OR operator (||) to assign a value to a variable if that variable doesn't already have a value. This is called the "define or" operator. Here's an example:
my $name;
$name ||= "John Smith";
In this example, $name is initially undefined. The ||= operator checks if $name is defined or not. Since it's not defined, $name is assigned the value "John Smith".
Here's another example:
my $age = 28;
$age ||= 30;
In this example, $age is already defined with the value 28. The ||= operator checks if $age is defined or not. Since it's already defined, $age is not assigned the value 30.
Note that the ||= operator assigns the new value only if the variable is undefined. If the variable has a false value (such as 0 or the empty string), it will still be assigned a new value using ||=. If you want to check for definedness and truthfulness, you can use the //= operator instead.