Why are PHP errors printed twice?

Question

Summary

Amazingly I could find nothing about this on Google or SO. When I throw an exception in PHP it appears in my console twice, complete with error message and stack trace. The first time it's printed it says "PHP Fatal error: ..." and the second time it just says "Fatal error: ...". I haven't tested this is the Apache plugin version.

Example

With some namespaces and paths shortened with '...' for safety:

$ php code/com/.../tabular_data.php
PHP Fatal error:  Uncaught exception 'Exception' with message 'File type not supported' in /home/codemonkey/.../tabular_data.php:56
Stack trace:
#0 /home/codemonkey/.../tabular_data.php(88): com\...\Tabular_Data->loadFromFile('/home/codemonke...', false)
#1 /home/codemonkey/.../tabular_data.php(95): com\...\Tabular_Data::fromFile('/home/codemonke...')
#2 {main}
  thrown in /home/codemonkey/.../tabular_data.php on line 56

Fatal error: Uncaught exception 'Exception' with message 'File type not supported' in /home/codemonkey/.../tabular_data.php:56
Stack trace:
#0 /home/codemonkey/.../tabular_data.php(88): com\...\Tabular_Data->loadFromFile('/home/codemonke...', false)
#1 /home/codemonkey/.../tabular_data.php(95): com\...\Tabular_Data::fromFile('/home/codemonke...')
#2 {main}
  thrown in /home/codemonkey/.../tabular_data.php on line 56

Question

I assume it has something to do with stderr and stdout both printing the error. In any case how do I ask PHP nicely to only print it once, preferably to stderr?

---

Version output

PHP 5.3.9 (cli) (built: Jan 11 2012 17:09:48)
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2012 Zend Technologies

The code

http://pastebin.com/iBUGJ2eY
This is the exact code that displays double exceptions for me, with namespaces and paths edited to foos. Note that I always get double exceptions in the command line on this installation. I'm all but certain that the issue lies in the PHP configuration.

Answer 1

Got it reproduced. The first error message is a result of the log_errors setting and goes to STDERR.

The second is a result of display_errors and goes to STDOUT.

Both settings can be altered during runtime. So in order to "ask PHP nicely", this suffices:

ini_set('log_errors', 1);
ini_set('display_errors', 0);

Answer 2

Like written in the answer of Linus Kleen the reason for the double messages is that the display_errors go to stdout. I found out that since php 5.2.4 this even happens when display_errors is set to 1 or "on".

To restore the normal behavoir it is the best way to define file where logged errors should be stored e.g. add this:

error_log = 'd:/logs/php_error.log'

to your php.ini. When the file for error_log is defined, you get only one message to stdout what you would need for testing. And for production state you can set display_errors to 0.