use Time::Local;

use constant ONE_DAY => 24 * 60 * 60;

my ($sec,$min,$hour,$mday,$mon,$year) = gmtime();
$mday = 1;

my $time = timegm($sec,$min,$hour,$mday,$mon,$year) - ONE_DAY;

print "Date: " . localtime($time) . "\n";

$mday = (localtime($time))[3];

print "Day of month: $mday\n";