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use strict;
use warnings;
...
    }
    return @content;
}

__CONTENT FILE 1__
2010-02-12_aaa,654
...
2010-02-14_bbb,754
2010-02-14_aaa,169
2010-02-14_ccc,965

__CONTENT FILE 2__
2010-02-12_aaa,654
...
2010-02-14_bbb,754
2010-02-14_aaa,169
2010-02-14_ccc,965

__OUTPUT__
2010-02-12_aaa,654
...
2010-02-14_bbb,1508
2010-02-14_ccc,965
2010-02-14_ccc,1930

__EXPECTED OUTPUT__
2010-02-12_aaa,1308
...
2010-02-14_aaa,338
2010-02-14_bbb,1508
2010-02-14_ccc,1930