PHP Simplest way to log actions

debug.logger.php

<?php
//just TEXT log any action, and info about it, like a purchase, use for backup/internal storage
//I use this for all types of requests, when dealing with online payments

/* LOG */
file_put_contents('logs/'.date('Y.m').'.pay.log','['.$_SERVER['REMOTE_ADDR'].'] '.date('Y.m.d-H:i:s').': Order ID : '.$order_id.', Error : '.$error.', Sum'.$payed_sum.', Transaction : '.$transaction_id.PHP_EOL,FILE_APPEND);

//I recommend to keep the comma, for eventual csv reading
//automatically creates a single file per month, keeping the logs small
//keeps the IP and time stamp in a nice juman form