In a new post to his blog Brian Moon describes a need he had for detecting if the client or user calling a PHP script was using an interactive terminal (TTY) or not:

Let's say I am trying to find out why some file import did not happen. Running the job that is supposed to do it may yield an error. Maybe it was a file permission issue or something. There are other people watching the alerts. What they don't know is that I am running the code and looking at these errors in real time.

Since the errors were being sent to the log file, they were lost to the client/user on the other end left staring at their script wondering what went wrong. He ended up with a solution (a pretty simple one too) that uses posix_ttyname and posix_isatty. He includes the little snippet of code he puts in his prepend file that checks for errors then checks for a TTY. If both are there, it turns off logging the errors to the file and sends them direct instead.