source: binary-improvements/7dtd-server-fixes/src/TelnetCommands/SayToPlayer.cs@ 93

using System;
using System.Collections.Generic;

public class SayToPlayer : ConsoleCommand
{
        private GameManager manager;

        public SayToPlayer (ConsoleSdtd cons) : base(cons)
        {
                manager = m_Console.gameManager;
        }

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

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

        public override void Run (string[] _params)
        {
                if (_params.Length < 2) {
                        m_Console.md000a ("Usage: sayplayer <playername|entityid> <message>");
                        return;
                }

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

                int entityId = -1;
                if (int.TryParse (_params [0], out entityId)) {
                        foreach (KeyValuePair<int, int> kvp in manager.connectionManager.mapClientToEntity) {
                                if (kvp.Value == entityId) {
                                        int clientid = kvp.Key;
                                        ClientInfo ci = manager.connectionManager.connectedClients[clientid];
                                        if (ci != null) {
                                                manager.connectionManager.networkView.RPC ("RPC_ChatMessage", ci.networkPlayer, new object[] {
                                                        message,
                                                        -1,
                                                        "Server (private)",
                                                        true
                                                        }
                                                );
                                                m_Console.md000a ("Message sent");
                                                return;
                                        }
                                }
                        }
                        m_Console.md000a ("Entity ID not found.");
                } else {
                        string destPlayerName = _params [0].ToLower ();
                        foreach (ClientInfo ci in manager.connectionManager.connectedClients.Values) {
                                Dictionary<int,int> d = manager.connectionManager.mapClientToEntity;
                                if (d.ContainsKey (ci.clientId)) {
                                        entityId = d [ci.clientId];
                                        string curName = manager.World.playerEntities.dict [entityId].EntityName;
                                        if (curName.ToLower ().Equals (destPlayerName)) {
                                                manager.connectionManager.networkView.RPC ("RPC_ChatMessage", ci.networkPlayer, new object[] {
                                                        message,
                                                        -1,
                                                        "Server (private)",
                                                        true
                                                        }
                                                );
                                                m_Console.md000a ("Message sent");
                                                return;
                                        }
                                }
                        }
                        m_Console.md000a ("Playername not found.");
                }
        }
}