If have tried using:

if (exists $fd{chk1} ) { push @columns }
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The "push" function needs one or more args after the array, which would be the value(s) to be pushed onto the array. Your push statement there (with just the array alone) is not doing anything at all. (Was that a copy/paste error in creating the post, or did you really miss that point in the original code?)

Update: As for your other attampt:

if ($fd{chk1} eq "Listname") {
$columns = $db->quote($fd{$_}) .",";
}
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That doesn't quite make sense either, because the "if" condition is testing  $fd{chk1} but the assignment statement inside the block is referring to  $fd{$_} -- and you haven't shown anything to suggest that $_ would actually equal "chk1" at that point (it probably does not).