I'm not sure how far you're going to get ... but I approach things a bit differently. I'm not disagreeing with ikegami at all here, but just your one parameter you're giving to execute. Instead of constructing a string by hardcoding everything you want to put in there, I prefer telling perl how to construct things and then using a list or array.

For example, instead of my $executable = "+$melville +$herman"; (which is the same as what you have - the perl compiler produces the same code either way), I prefer doing the long-winded version such as:

my @searches = get_searches(); # e.g., qw(melville herman)
my $search_param = join ' ', map { "+$_" } @searches;
$ding->execute($search_param) or die DBI->errstr();
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I've only really extended by another line, though if you count opcodes, mine will be much longer. The difference? Ease of change. Adding another keyword is simple - just have get_searches produce a longer list (which could be hardcoded itself, doesn't matter). You want to automatically handle multiple words by quoting them? Also simple: just change the map, e.g., map { /\s/ ? qq[+"$_"] : qq[+$_] }. It's all really straight-forward. But I deal in change more than I deal with original code, so that type of flexibility has always been important to me. Yes, it's less readable. But it's the least unreadable for the flexibility. And, after a bit more experience, it becomes not much less readable than your original version.