push @foo, [ split /:/ ] while <>;
print map { "$_->[0]\n" } sort { $a->[2] <=> $b->[2] } @foo;
# Two lines, for clarity.
# Of course I could have used another map.

##</code><code>##

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$