while (<>) {
    2 == (my($x, $y) = split " ") or die "wrong number of fields";
    ...
}

##</code><code>##

wrong number of fields at -e line 1, <> line 1.

##</code><code>##

$ perl -e 'warn 0+(@x = split " ", "foo bar\n");'
2 at -e line 1.
$ perl -e 'warn 0+(($x, $y) = split " ", "foo bar\n");'
3 at -e line 1.
$