my $sqlcount = 'SELECT COUNT(*) FROM grp_def WHERE grp_name = ?';

my $sth = $dbh->prepare($sqlcount)
  or die "Cannot prepare: " . $dbh->errstr();
$sth->execute($grp_name)
  or die "Cannot execute: " . $sth->errstr();

my $occurences = $sth->fetchrow_arrayref->[0];

print "result: $occurences\n";