Introduction to PHP

Spot on, Nathan. The difference between single and double quotes is that in single quotes, the PHP parser doesn't interpret any of the contents and just presents them literally. This includes not translating variables into their values, and it also means that escaped characters (like \t for tag, \n for line-feed) are not translated either. Single-quotes are good when you want the string to be totally literally with no substitution.

Sorry that printf() was baffling. I was just sharing a completely different way -- "for fun", as I wrote -- but since I brought it up, yes, you're basically right. printf() uses substitution placeholders in its format string. %s means to render a variable as a string (as opposed to as an integer, float, or some other type of value). It maps the placeholders in order to the variable arguments. In this case, then, the first %s is replaced by $chunk1 formatted as a string, and the second %s is replaced by $chunk2. You can actually get quite fancy with the placeholders, that was a very basic example. I just threw it in for fun, but great job tackling it and you intuited well.

As for using Linux almost exclusively, keep in mind that if you contribute or share your code, it may find its way onto a Windows computer. I recommend using PHP_EOL simply because it's a good habit to get into. It'll never be wrong, and it can be very helpful in cases where you might not have expected the code could eventually end up on Windows and does. Or vice versa for the Windows crowd who don't expect to run their code on Linux, a Unix (which includes Mac OS X).