For little problems fix 'em with little solutions. We were in a project where we just had apache and php installed and we needed save emails from a form with ajax.

storingEmailsInFile.php

<?php

function saveEmail($email){
	$file = 'emails.txt';
	return file_put_contents($file, PHP_EOL.$email, FILE_APPEND | LOCK_EX);
}


function validateEmail($email) {
	return filter_var($email, FILTER_VALIDATE_EMAIL);
}

function sendJSONResponse($message, $error){
	$data = array(
		'message' => $message,
		'error' => $error
	);

	header('Content-type: application/json');
	echo json_encode( $data );
}


if ($_SERVER['REQUEST_METHOD'] === 'POST') {
	if(isset($_POST['goodfetch_email'])){
		if(validateEmail($_POST['goodfetch_email'])){
			if (saveEmail($_POST['goodfetch_email'])) {
				sendJSONResponse('Email saved successfully!', false);
			}else{
				sendJSONResponse('One monkey stole our database, but some of our engineers are about to reach it, try later please.! XD', true);
			}
		}else{
			sendJSONResponse('Email validation faild.', true);
		}
	}else{
		sendJSONResponse('You have to send an email.', true);
	}
	
}else{
	header('Location: http://goodfetch.com');
}

?>