source: binary-improvements/7dtd-server-fixes/src/TelnetCommands/SayToPlayer.cs@ 114

using System;
using System.Collections.Generic;

public class SayToPlayer : ConsoleCommand
{
        public SayToPlayer (ConsoleSdtd cons) : base(cons)
        {
        }

        public override string Description ()
        {
                return "send a message to a single player";
        }

        public override string[] Names ()
        {
                return new string[] { "sayplayer", "pm" };
        }

        private void SendMessage (ClientInfo _receiver, ClientInfo _sender, string _message)
        {
                string senderName;
                if (_sender != null) {
                        PrivateMassageConnections.SetLastPMSender(_sender, _receiver);
                        senderName = CommonMappingFunctions.GetPlayerName (_sender);
                } else {
                        senderName = "Server";
                }
                CommonMappingFunctions.GetConnectionManager ().networkView.RPC ("RPC_ChatMessage", _receiver.networkPlayer,
                                new object[] {
                        _message,
                        -1,
                        senderName + " (PM)",
                        true
                }
                );
                string receiverName = CommonMappingFunctions.GetPlayerName (_receiver);
                m_Console.SendResult ("Message to player " + (receiverName != null ? "\"" + receiverName + "\"" : "unknownName") + " sent with sender \"" + senderName + "\"");
        }

        private void RunInternal (ClientInfo _sender, string[] _params)
        {
                if (_params.Length < 2) {
                        m_Console.SendResult ("Usage: sayplayer <playername|entityid> <message>");
                        return;
                }

                string message = _params [1];
                for (int i = 2; i < _params.Length; i++) {
                        message += " " + _params [i];
                }

                ClientInfo receiver = CommonMappingFunctions.GetClientInfoFromNameOrID (_params [0], true);
                if (receiver != null) {
                        SendMessage (receiver, _sender, message);
                } else {
                        m_Console.SendResult ("Playername or entity ID not found.");
                }
        }

        public override void ExecuteRemote (string _sender, string[] _params)
        {
                try {
                        this.m_Console.SendResult (string.Format ("{0} executing remote command '{1}' {2}", _sender, this.Names () [0], string.Join (" ", _params)));
                        ClientInfo ci = CommonMappingFunctions.GetClientInfoFromSteamID (_sender);
                        RunInternal (ci, _params);
                } catch (Exception e) {
                        Log.Out ("Error in SayToPlayer.ExecuteRemote: " + e);
                }
        }

        public override void Run (string[] _params)
        {
                try {
                        RunInternal (null, _params);
                } catch (Exception e) {
                        Log.Out ("Error in SayToPlayer.Run: " + e);
                }
        }
}