How do you set a default value of a scalar?

$x = defined $x ? $x : $DEFAULT;

$x ||= $DEFAULT;

$x //= $DEFAULT;
examples/feature/defined_or.pl
#!/usr/bin/perl
use strict;
use warnings;

my $val;
print defined $val ? "defined\n" : "not defined\n";   # not defined

$val //= 42;

print "$val\n";   # 42



$val = 0;

print "$val\n";   # 0

$val //= 42;

print "$val\n";   # 0