Steps:

1. Find the epoch at 00.00 hrs for Date 1 of current month, current year.

2. Subtract 1 from that to reach previous day and convert that epoch again into date.

3. Grab the date and/or month value from it.

#!/usr/bin/perl -w
use strict;
use Class::Date;

my $date = new Class::Date [`date +%Y`, `date +%m`, 1, 0, 0, 0];

my $curMonthEpoch = $date->epoch;
my $prevMonthEpoch = $curMonthEpoch - 1;

print "Last Date of Prev Month=".`date --date='\@$prevMonthEpoch' +%d`
+;
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