my $foo ||= 1; # $foo is set to '1' if it was previously a false value

my $bar //= 1; # $bar is set to '1' only if it was undefined (0 and empty string don't count).

##</code><code>##

sub routine {
     my $input_ref = {@_};
     my $var1      = defined $input_ref->{var1} ? $input_ref->{var1} : 1;
}