When you login, that is, log in, the computer starts up a program called a shell just for you and then does housekeeping by placing you into your home directory. Your home directory file system is the top of your workspace, and, if you so desire, you can keep all other users out of it. While you may use this workspace any way you wish, in Workstation Setup and Use, we illustrate the making of subdirectories that keep your work (and play) separate and organized. Just as it is a poor practice to throw all your papers into one pile on your desk, it is also poor practice to do all your work in your home directory.
Like Eliot's cats, your Unix home directory can be called by at least three names. You can call it $HOME, or ~, or explicitly, /u/rubin. You can refer to the home directory of another user, paul, as ~paul. (Note: the ~ forms are actually C and Korn shell variations.)
A user's home directory often contains some files beginning with a ``.'' which help customize Unix programs to just the way the user likes them. (Since files beginning with ``.'' are not normally visible with the list command ls, you must say ls -a to see them.) At some point when you execute certain commands or run certain programs, these programs look for the dot files and then read them to determine your preferences. The dot files' formats and uses are described in the documentation for each program or command, and samples may be found in Workstation Setup and Use, in Looking through X Windows, and in Sample Dot Files. Brief descriptions of some of the more common and useful ones are in Common and Useful Dot Files .