In a post to his site Leonid Mamchenkov shares an interesting output bug he came across in his work developing cron jobs and how they handled his errors.

We came across this PHP bug at work today. But before you go and read it, let me show you a use case. See, if you can spot the problem. We had a cron job script which [ran a PHP script and echoed a string when complete].

[...] We use similar code snippets all over the place, and they work fine. This particular one was a new addition. So the cron job ran and “Updating products failed” part happened. Weird. The PHP script in question has plenty of logging in it, but nothing was logged.

After adding more and more logging to the process and PHP script, nothing obvious was standing out. Finally, they noticed that the filename was incorrect but normally that would cause an error in the PHP command line execution. The tricky part here was in how PHP handled its errors. Their error_log and display_errors settings were such that the PHP "missing file" error was being swallowed up and not displayed.