Hello Monks,

I know this title sounds like a very common issue, but I came here to seek your wisdom on my observation. I have a script that processes some values and then stores them into an array.

While I was trying to observe if the array contains element(s) I found several tutorials and documentation online that should work, such as exists, defined, How do I test if an array is empty or not? etc.

I created a small demonstration script to replicate my curiosity question.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @a = ();
my @b = ( undef );

print "\@a is not Empty\n" if (@a);
print "\@b is not Empty\n" if (@b);
print "\@a is not Empty grep\n" if grep { defined($_) } @a;
print "\@b is not Empty grep\n" if grep { defined($_) } @b;

print Dumper \@a;
print Dumper \@b;
[download]

Sample of output:

@b is not Empty
$VAR1 = [];
$VAR1 = [
          undef
        ];
[download]

Now that I am thinking about it more, still undef it occupies a position on the array. Possibly this is the reason that if (@b) still prints the text.

From my point of view in cases that a script can contain undef values someone should use the if grep { defined($_) } @b functionality to determine if the array is empty, alternatively a simple if condition should do the work.

Can someone provide a bit of more information regarding undef. Thank you in advance for your time and effort.