headers already sent

[smallcompany]

For years, I've been using PHP to email 404 errors. Since recently, on one of the sites, this message started being logged every time 404 was triggered:

[18-Mar-2015 12:08:04 America/New_York] PHP Warning: Cannot modify header information - headers already sent by (output started at /path/error-404.php:1) in /path/error-404.php on line 2

PHP code is at the very top of 404 custom file, above the HTML code:

<?php 
header('Status: 404 Not Found', null, 404);
$from_header = "From: [e-mail]\r\n";
$to = "[e-mail]";
$subject = "404 Error";
$today = date("D M j Y g:i:s a T");
$ip = getenv ("REMOTE_ADDR");
$requri = getenv ("REQUEST_URI");
$servname = getenv ("SERVER_NAME");
$pageload = $ip . " tried to load http://" . $servname . $requri ;
$httpagent = getenv ("HTTP_USER_AGENT");
$httpref = getenv ("HTTP_REFERER");
$message = "$today \n\n$pageload \n\nUser Agent = $httpagent \n\n$httpref ";
mail($to, $subject, $message, $from_header);
?>

I have another website with the same hosting company, same package, different server. No such errors are being produced, nor I get them on other sites hosted with other companies.

I wonder about how to troubleshoot this.

Thanks

[smallcompany]

I wonder about how to troubleshoot this.

Continue searching the web.

It was about how the file was saved, that is, encoded.

When I compared the two files in Notepad++, the "good" one was set as "Encode in UTF-8 without BOM" while the "offender" was just "Encode in UTF-8"

I found a hint here: [php.net...] (where else about PHP, eh?)

Anyway, yet another case of rush to a forum. Still, without rushing, there would be no this post which I hope may help some in the future.

Cheers!

[lucy24]

The underlying lesson is: Instruct all your text editors not to use a BOM ever, because there's honestly no need for it and it can do more harm than good :)