What database? You could also just write a SQL solution..

As for perl, here's a Date::Calc solution:

use Date::Calc qw(Today Add_Delta_YMD Days_in_Month);
my ($year, $month, undef) = Add_Delta_YMD( Today(), 0, -1, 0 );
printf "start: %04d-%02d-%02d\n", $year, $month, 1;
printf "  end: %04d-%02d-%02d\n", $year, $month, Days_in_Month($year, 
+$month);
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