You can just eval the bit where you want to get the variable's value:

foreach my $f (@fields) {
    my $val = eval qq{ \$fromQuery::$f };
    next unless $val;

    push(\@where,        $val);
    push(\@searchString, $val);
}
[download]

But I am sure that dragonchild's solution is faster. The only gotcha is that it won't run under strict but no strict 'refs'; in the correct scope will turn off that check:

foreach my $f (@fields) {
    no strict 'refs';  # This will only last in this scope

    my $val = ${ "fromQuery::$f" };
    next unless $val;

    push(\@where,        $val);
    push(\@searchString, $val);
}
[download]

-ben