Actually, you cannot depend on anything in the environment, especially not the path. (Well, you can, until you start running financial applications over the web. Then, you can't.) All of that is considered tainted by -T.
We are the carpenters and bricklayers of the Information Age.
Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.
Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.