use DateTime;

my $dt = DateTime->new(year=>2017,month=>3,day=>1);
print $dt->ymd, "\n";

print "-30 days: ",
	$dt->clone->subtract(days=>30)->ymd, " ";
system('date','+%Y-%m-%d','-d 2017-03-01 -30 days')==0 or die $?;

print "-1 month: ",
	$dt->clone->subtract(months=>1)->ymd, " ";
system('date','+%Y-%m-%d','-d 2017-03-01 -1 month')==0 or die $?;

__END__

2017-03-01
-30 days: 2017-01-30 2017-01-30
-1 month: 2017-02-01 2017-02-01