[root@ip:/tmp] ssh root@ip "sudo -u bob date"
root@ip's password: 
sudo: sorry, you must have a tty to run sudo
[root@ip:/tmp]
but ssh -t root@ip "sudo -u bob date" solves the problem 

##</code><code>##

use Carp qw(carp confess croak);
use Net::SSH2;
my $host = "ip";
my $user = "root";
my $pass = "mypassword";

# Connect to host
my $ssh = Net::SSH2->new();
if (! $ssh->connect($host)) {
print "Failed connection to $host\n";
exit(1);
}
if ($pass ne "") {
if (! $ssh->auth_password($user,$pass)) {
print "FAILED SCP password authentication for $username to $host\n";
exit(1);
}
} else {
print "FAILED SCP not the correct credentials provided in config file\n";
exit(1);
}
my $chan = $ssh->channel();
$chan->exec($ARGV[$0]);
$stdout = undef;
$chan->read( $stdout, 10000 );
$chan->close();
print $stdout;
$ssh->disconnect();
exit(0); 

##</code><code>##

perl myssh.pl "sudo -u bob date" won't work
perl myssh.pl "date" works and gives the date command output.