A common synonym for a Unix shell, or for the interface any computer program presents, is an environment. An environment is typically a collection of concepts that expresses the things a computer does in terms designed to be understandable and coherent, and a look and feel that is comfortable.
For example, your desk at work is an environment. Concepts involved in desk work usually include memos, phone calls, letters, forms, etc. The tools on or in your desk that you use to deal with these things include paper, staples, envelopes, pens, a telephone, a calculator, etc. Every one of these has a set of characteristics that express how you use it; such characteristics range from location on your desk or in a drawer (for simple tools) to more sophisticated things like which numbers the memory buttons on your phone are set to. Taken together, these characteristics make up your desk’s look and feel.
You customize the look and feel of your desk environment by putting pens where you can most easily reach them, programming your phone buttons, etc. In general, the more customization you have done, the more tailored to your personal needs — and therefore the more productive — your environment is.
Similarly, Unix shells present you with such concepts as files, directories, and standard input and output, while Unix itself gives you tools to work with these, such as file manipulation commands, text editors, and print queues. Your Unix environment’s ...