How can I check if a value is undef in Perl?

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.

possible duplicate of [How do I check if a Perl scalar variable has been initialized?](http://stackoverflow.com/questions/3738836/how-do-i-check-if-a-perl-scalar-variable-has-been-initialized) — brian d foy, Sep 22 '10 at 13:47

score 10 · Accepted Answer · answered Sep 22 '10 at 07:44

10

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

one liner

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

answered Sep 22 '10 at 07:44

Bob

`//` is a short-circuit operator, so it would be useful if you had a code path you want to execute conditionally based on the definedness of a single value. I can't think of a use here, but TMTOWTDI. – Bob Sep 22 '10 at 08:02
@David B, `//` is defined-or, so it can only be used to calculate "at least one defined". To get "at least one undef", you'd need a defined-and operator, which doesn't (currently) exist. – cjm Sep 22 '10 at 14:52

score 1 · Answer 2 · answered Sep 22 '10 at 10:12

1

expanding on Bob's answer, in some cases, you might want to grab the actual count

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

answered Sep 22 '10 at 10:12

erickb

2 Answers2