#!/usr/local/bin/perl -wl
use Time::Local;
use POSIX 'strftime';

sub get_yesterday {
   my $date = shift;
   my ($year, $month, $day) = split/-/,$date;
   my $time = timegm(0, 0, 12, $day, $month-1, $year);
   return strftime "%y-%m-%d", gmtime($time - 24*60*60);
}

print get_yesterday("2005-04-01");