print OUTPUT "$_,$output{$_}\n" for sort keys %output;

##</code><code>##

2010-02-12_aaa,1308
2010-02-12_bbb,748
2010-02-12_ccc,316
2010-02-13_aaa,1490
2010-02-13_bbb,1572
2010-02-13_ddd,1704
2010-02-14_aaa,338
2010-02-14_bbb,1508
2010-02-14_ccc,1930