in reply to Help understanding a single line of perl: my $count = $row[0] ? $row[0] : 0;

?: is the conditional operator. See perlop for documentation. In short, 
cond ? then_expr : else_expr

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is similar to 
if (cond) { then_expr } else { else_expr }

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except it can be used inside another expression. It returns the value of then_expr or else_expr as appropriate. That means 

my $count = $row[0] ? $row[0] : 0;

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is short for 
my $count;
if ($row[0]) {
    $count = $row[0];
} else {
    $count = 0;
}

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Update:

It could also have been written as 

my $count = $row[0] || 0;

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It seems to me it's trying to avoid assigning undef to $count, using zero instead when the situation occurs.

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Re^2: Help understanding a single line of perl: my $count = $row[0] ? $row[0] : 0;
by Tanktalus (Canon) on Aug 21, 2009 at 18:50 UTC

    Well, it's probably closer to: 

    my $count = do {
  if ($row[0]) {
    $row[0];
  } else {
    0
  }
};

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    but that's less readable to the uninitiated than what you have. :-P

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[d/l]
      if already returns the right thing. It's simply a parser check that prevents it from being used as an expression. (But I guess you know that.)

      I would have used do if it would have made it equivalent, but since it didn't, it was more readable to explain do rather than using do.

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[d/l]
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Re^2: Help understanding a single line of perl: my $count = $row[0] ? $row[0] : 0;
by kdmurphy001 (Sexton) on Aug 21, 2009 at 18:59 UTC
    Ah, yes that makes sense. I added a CASE statement to the sql statement but I think that was unnecessary. Thank you so much!
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