This is a sample Telegram bot written in PHP.

sample-telegram-bot.php

<?php

/*
* Sample Telegram Bot Source Code
*
* @author  Tadeh Alexani
* @version 1.00, 2017-09-06
* PHP
*/

/*
* Follow these steps to set-up your bot:
*
* 1- Setup your bot with @BotFather (You can follow the link below) :
* http://telegra.ph/Set-up-your-bot-with-BotFather-09-06
*
* 2- After you received your bot authorization token JUST SAVE IT SOMEWHERE!! :D
*
* 3- Prepare a SSL server for your .PHP file (It should be like https://example.com
*
* 4- Set Webhook for your bot by following this link:
* https://api.telegram.org/bot<token>/setWebhook?url=https://mywebsite.com/path/to/giveawaysbot.php
*
* 5- Happy Coding! You can easilly test this file on your own server :)
* Let me know if you have any question! @tadeh & hi@TadehAlexani.com
*
*/

$apiLink = "https://api.telegram.org/bot[YOUR_API_KEY]/";
$update = file_get_contents("php://input");
$updateArray = json_decode($update, TRUE);
$username = $updateArray["message"]["chat"]["username"];
$userID = $updateArray["message"]["chat"]["id"];
$chatID = $updateArray["message"]["chat"]["id"];
$messageText = $updateArray["message"]["text"];

$keyboard = array(
    ["ONE"], ["TWO"], ["THREE"]
);
$resp = array("keyboard" => $keyboard, "resize_keyboard" => true, "one_time_keyboard" => true);
$reply = json_encode($resp);

if ($messageText == "/start") {
    $welcomeText = "This is a Simple Bot!";
    file_get_contents($apiLink . "sendmessage?chat_id=$chatID&text=" . $welcomeText . "&reply_markup=" . $reply);
	
} else if ($messageText == "ONE") {
    $output = "ONE";
    file_get_contents($apiLink . "sendmessage?chat_id=$chatID&text=" . $output . "&disable_web_page_preview=true&parse_mode=HTML&reply_markup=" . $reply);
	
} else if ($messageText == "TWO") {
    $output = "TWO";
    file_get_contents($apiLink . "sendmessage?chat_id=$chatID&text=" . $output . "&disable_web_page_preview=true&parse_mode=HTML&reply_markup=" . $reply);

} else if ($messageText == "THREE") {
    $output = "THREE";
    file_get_contents($apiLink . "sendmessage?chat_id=$chatID&text=" . $output . "&reply_markup=" . $reply);
	
} else {
    $errorMsg = "You entered a wrong command!"
    file_get_contents($apiLink . "sendmessage?chat_id=$chatID&text=" . $errorMsg);
}
?>