It might have gone by you - JavaFan's question was more rhetorical, as the differences in output of the following code show you:

use strict;

my $rowRef = {
    foo => 'foo value',
    bar => 'bar value',
};

my $rowName = 'bar';
for my $rn ($rowName, '$rowName') {
    my $rowValue;
    if (exists $rowRef->{$rn}) {
        $rowValue = $rowRef->{$rn}
    } else {
        $rowValue = '<does not exist>';
    };
    print "rowRef for '$rn' is '$rowValue'\n";
};
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