PHP script to automatically deploy from github webhooks

gitploy.php

<?php
/**
 *
 * AUTODEPLOY GITHUB REPO ON HOSTING
 * 
 * @author Vincent Lalanne <info@fugu.fr>
 *
 *
 * Step 1: create the SSH key on your hosting 
 * https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys--2
 * 
 * Step 2: add your ssh key on GitHub
 * in your profile > settings > SSH and GPG keys 
 * or in your repo > settings > Deploy keys
 *
 * Step 3: clone your GitHub repo on your hosting and checkout the branch your want autodeploy
 *
 * Step 4: add and commit this script into a directory in your repo
 * (you can use it as a submodule)
 *
 * Step 5: create a webhook on GitHub to call this script
 * https://developer.github.com/webhooks/creating/
 * Set your url to this script, ex. http://mydomain.tld/gitploy/gitploy.php
 * Choose "application/x-www-form-urlencoded" as content-type
 * Choose "Just the push event." as trigger
 *
 *
 * Alternately you can follow the instructions on this page (french): 
 * https://www.alsacreations.com/article/lire/1647-synchroniser-son-serveur-web-avec-github.html
 *
 *
 * Troubleshootings
 *
 * If the script failed, you should edit/create the ~/.ssh/config file on your hosting
 * and add those lines
 *
 * Host github.com
 *    Hostname ssh.github.com
 *    Port 443
 * 
 */

/**
 * Check if the request comes from GitHub Webhook
 * else return 401 unauthorized error
 */
$headers = getallheaders();
$userAgent = $headers['User-Agent'];
$deploy = true;

if ( empty($userAgent) || !preg_match('/^GitHub\-Hookshot\//i', $userAgent)) {
    header('HTTP/1.0 401 Unauthorized');
	exit;
}

function getGitBranch()
{
	// Get the current ref from git HEAD
    $shellOutput = shell_exec("cd ..; cat .git/HEAD");
    // Extract branch name
    $branch = preg_replace('/^ref:\srefs\/heads\/([0-9a-zA-Z_\-]+)$/i', '$1', $shellOutput);
    // Remove line breaks
    $branch = preg_replace( "/\r|\n/", "", $branch );

    return !empty($branch) ? $branch : null;
}

if (!empty($_POST['payload'])) {
	// If payload exists, get the pushed branch 
	// and compare it to the current branch
	$payload = json_decode($_POST['payload']);
	$branch_pushed = preg_replace('/refs\/heads\//i', '', $payload->ref);
	$current_branch = getGitBranch();

	// Allow to deploy or not
	$deploy = $current_branch == $branch_pushed;
}

echo "Need to deploy: " . ($deploy ? "true" : "false") . "\n";

if ($deploy) {

	/**
	 * The ordered command list your want to execute
	 */
	$commands = [
	    'whoami',
	    'cd ../',
	    'pwd',
	    'git checkout -f',
	    'git reset --hard',
	    'git pull',
	    'git status',
	];

	/**
	 * Run all command and echo the result for logs
	 */
	echo shell_exec(implode(' && ', $commands));
}