Ok, I solved my problem. The problem was I erroneously thought I could get a DBI::errstr based on the $sth prepare statement alone....you need an execute too. doh!! So for the benefit of others looking for an answer, here is my code which works fine:

#####################################################
$entrysql->bind('<Return>',[sub {
                            $sql = $entrysql->get;
eval {
      local $dbh->{AutoCommit} = 0;
      my $sth = $dbh->prepare("select $mainstr from info $sql")
                                     or die DBI::errstr;
      $sth->execute or die DBI::errstr;
     };

if($@){ print chr(07),  $@, "bad sql\n"; return}

print "seems ok\n";

#....continue on and do it for real
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