TIMTOWTDI. If you want to drop everything after the first ".", you could modify your split a little:

perl -le 'my $string = "foo.bar.aaa"; ($_) = split(/\./,$string,2); print;'

or you could use a rexexp:

perl -le '$_ = "foo.bar.aaa"; s/\..*$//; print;'

or

perl -le '($_) = "foo.bar.aaa"=~ /^(.*?)\./; print;'