<Appendix D> Just enough UNIX
Since the UNIX operating system may be unfamiliar to many of you, and since many workstations on the net use UNIX, it may help some readers to summarize some of the peculiarities of UNIX. One day you may be logged on to a UNIX machine. Nowadays, like many operating systems, UNIX hides behind a graphical user interface like the X Windows system. Occasionally—and networking is unfortunately one of those occasions— its quirks like file-naming and directory hierarchy peek through.
This Appendix gives you just enough UNIX to avoid some pitfalls and issue commands needed to transfer files. The basic commands you need to know for any system are how to display directories and list the contents of files, how to name files, and how to get help about the system. UNIX commands are just as quirky as MS-DOS, VMS, RSX, VM, or any other operating system that uses a command language. Fortunately, they are no harder.
<Section D.1> Basic Commands for Getting Around
ls : list current directory
ls -l : longer listing, with file length in bytes
cd mydir : move down one level in the hierarchy to directory "mydir"
cd .. : move up one directory in the hierarchy
<Section D.2> Hierarchical File System
Files in UNIX are arranged in a hierarchy or tree structure.