How to use the defined-or operator in Perl

The // operator returns its left operand if it's defined, otherwise returns the right operand. This is different from || which checks for truth:

use v5.10;
use strict;
use warnings;

my $value = 0;
my $undef;

# Using || (checks for truth)
my $result1 = $value || "default";  # Returns "default" (0 is false)

# Using // (checks for definedness)
my $result2 = $value // "default";  # Returns 0 (0 is defined)
my $result3 = $undef // "default";  # Returns "default" (undef not defined)

say "result1: $result1";  # default
say "result2: $result2";  # 0
say "result3: $result3";  # default

Use // when you want to distinguish between false values (0, empty string) and undefined values.