Why is this only returning x.z in $first and nothing in $second?

Because split consumes what you are splitting on, and you are splitting on .y in your test case. However,

If the PATTERN contains capturing groups, then for each separator, an additional field is produced for each substring captured by a group (in the order in which the groups are specified

so you could do <contrived>

my $str = "x.z.y";
my ($first,$second) = split(/\.([^.]*)$/,$str);
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</contrived> Other alternatives include split, pop and join; toolic's regex (what I'd actually do); or even reverse, index and substr. Good times.