A simple static class for dumping information to a log file of your choosing. For more info, see https://philkurth.com.au/tips/a-php-class-for-dumping-data-to-a-separate-log-file/

Dump.php

<?php

/**
 * Class Dump
 * A simple static class for dumping data to a separate log file to aid debugging and development.
 *
 * @author Phil Kurth <phil@philkurth.com.au>
 */
class Dump {


	public static $logfile;


	/**
	 * Logs data to log file
	 *
	 * @param mixed $data
	 * @param string $mode Specifies write mode ('a' for append || 'w' for write)
	 * @param boolean $pretty If true, var_export is used
	 * @param boolean $informative If true, informative header is printed
	 *
	 * @throws \Exception
	 */
	static function log( $data, $informative = false, $mode = 'a', $pretty = true ) {

		if ( ! self::$logfile ) {
			throw new \Exception( 'Debug::$logfile is not set' );
		}

		$file_location = self::$logfile;

		$datetime = new DateTime; // current time = server time
		$otherTZ = new DateTimeZone( 'Australia/Melbourne' );
		$datetime->setTimezone( $otherTZ ); // calculates with new TZ now

		$bt = debug_backtrace();
		$file = "Calling file: " . basename( $bt[0]['file'] );
		$line = "Line: " . $bt[0]['line'];

		$info = '';

		if ( $informative ) {
			$info = ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n";
			$info .= $datetime->format( 'm/d/Y h:i:s a' ) . "\n";
			$info .= $file . "\n";
			$info .= $line . "\n";
			$info .= ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n";
		}

		// Better boolean logging
		if ( $data === false ) {
			$data = '(bool)FALSE';
		} elseif ( $data === true ) {
			$data = '(bool)TRUE';
		}

		if ( $pretty ) {
			$info .= print_r( $data, true );
		} else {
			$info .= var_export( $data, true );
		}

		$info .= $informative ? "\n\n" : "\n";

		$file = fopen( $file_location,
			$mode ) or print( '<div style="background-color:#db514d;color:white;text-align:center;padding:10px;">Cannot open log file for logging</div>' );
		fwrite( $file, $info );
		fclose( $file );
	}

}

usage-example.php

<?php

// Include and configure the class. I usually do this in my wp-config.php
// file but you could do this in a theme or a plugin instead. 
require 'class-dump.php';
Dump::$logfile = __DIR__ . '/dev.log';

// Need to dump something to the log while you are working? Easy!
Dump::log('some data');