As a small variant, you can calculate a key by 100*year+month, assuming that month will always be two digit at most... 
my @sorted = sort {
    ($a =~ /\.([0-9]+)-([0-9]+)\./, 100*$1+$2) 
<=> ($b =~ /\.([0-9]+)-([0-9]+)\./, 100*$1+$2)
} @strings;

[download]
or would it be ok to insert the missing zero? 
map { s/-(\d)\./-0\1./ } @strings;
my @sorted = sort @strings;

[download]
(Make sure the regexp does not match elsewhere in your strings.)

In reply to Re^2: Sort an array of strings based on two fields by hdb
in thread Sort an array of strings based on two fields by luca76

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