set year = 2015 
set month = 2 
set start = $zdateh(year_"-"_month_"-1",3) 
set end = $zdateh((year+$select(month=12:1,1:0))_"-"_(month+$select(month=12:-11,1:1))_"-1",3)-1 
write $zdate(start,3)_" / "_ $zdate(end,3)

// 2015-02-01 / 2015-02-28