如何在Perl中检查值是否为undef？

Question

Best asked by an example:

my $var1=1;
my $var2;
my $var3=3;

# say "at least one undef" if at least one of $var1, $var2, $var3 is undef

Obviously I can explicitly loop and do that, but I always like to find one liners that achieve the same result.

Answer 1

if (grep { !defined } $var1, $var2, $var3) {
  say 'at least one undef'
}

one liner

say 'at least one undef' if grep { !defined } $var1, $var2, $var3;

Answer 2

扩展鲍勃的答案，在某些情况下，你可能想要抓住实际的数量

say 'has ', scalar ( grep { not defined } $var1,$var2,$var3 ),' undef';