Akash Mehta shares a helpful hint in this new post to the Developer Tutorials Blog today - testing out PHP code via the command line PHP binary.
Thankfully, PHP provides the interactive shell, allowing you to test out PHP interactively with immediate feedback. Here's how to take advantage of this mature feature of PHP.
With the help of the "-a" flag on the command line, the PHP binary will hand you an environment where you can code PHP and instantly see the results. He does mention a few quirks that make it different than working with PHP through a web server, namely moving in and out of code blocks and remembering to finish out with a semi-colon when the line is done.