You can also use Time::Local, as shown below. It's not the friendliest module, but it comes with perl.

use Time::Local qw( timegm_nocheck );

my ($y, $m, $d) = (localtime)[5,4,3];
$y += 1900;
$m += 1;

my $ds = 1;
my $de = (gmtime(timegm_nocheck(0,0,0, (1-1), ($m+1)-1, $y)))[3];

printf "start: %04d-%02d-%02d\n", $y, $m, $ds;
printf "  end: %04d-%02d-%02d\n", $y, $m, $de;
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Keep in mind the last day of the month is the day before first day of the next month.