Using the GRT: 

print for @a;;
xxxxxx.2013-2.yyyyy
xxxxxx.2013-11.yyyyy
xxxxxx.2013-10.yyyyy
xxxxxx.2012-52.yyyyy
xxxxxx.2013-3.yyyyy
xxxxxx.2012-51.yyyyy
xxxxxx.2012-50.yyyyy
xxxxxx.2013-1.yyyyy
xxxxxx.2013-4.yyyyy

@b = map{ 
    unpack 'x[NN]a*', $_ 
} sort map{ 
    m[(\d{4})-(\d+)]; 
    pack 'NNa*', $1, $2, $_ 
} @a;;

print for @b;;
xxxxxx.2012-50.yyyyy
xxxxxx.2012-51.yyyyy
xxxxxx.2012-52.yyyyy
xxxxxx.2013-1.yyyyy
xxxxxx.2013-2.yyyyy
xxxxxx.2013-3.yyyyy
xxxxxx.2013-4.yyyyy
xxxxxx.2013-10.yyyyy
xxxxxx.2013-11.yyyyy

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

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