I am trying to understand two snippets of code, that have different behaviors that I do not immediately grasp. Consider:

use strict;
use Data::Dumper;

my @res = grep $_ split(",", "a,b,c,d,,f,,h");
print Dumper(\@res);

my @res2 = grep { $_ } split(",", "a,b,c,d,,f,,h");
print Dumper(\@res2);
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When ran, it returns

$VAR1 = [
          'a',
          'c'
        ];
$VAR1 = [
          'a',
          'b',
          'c',
          'd',
          'f',
          'h'
        ];
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I understand the second example, as I am evaluating the "truth" of the elements I am iterating over. I do not understand the output of the first dump, when given just "$_". I did look at grep's perldoc, hoping for an ounce of clairvoyance, but to no avail.