use DateTime;
use DateTime::Format::Strptime;

# string - input from user or something else
my $time = '2009-11-30';

# Create a parser that can read YYYY-MM-DD Format
my $parser = DateTime::Format::Strptime->new(
    pattern   => '%Y-%m-%d',
    time_zone => 'Europe/Berlin',
);

# Parse the String
my $dt = $parser->parse_datetime($time);

# Subtract one Day
$dt->subtract( days => 1 );
print $dt, "\n";