Generally speaking, a network lets two or more computers communicate and work together. Partly because of its open design, UNIX has been one of the operating systems where a lot of networking development is done. Just as there are different versions of UNIX, there are different ways and programs to use networks from UNIX.
We don't cover networking in this book (1.32). This article has a summary of some common UNIX networking and communications utilities.
A worldwide network of computers. Internet users can transfer files, log into other computers, and use a wide range of programs and services.
The World Wide Web is a fast-growing set of information servers on the Internet. The servers are linked into a hypertext web of documents, graphics, sound, and more. Point-and-click browser programs turn that hypertext into an easy-to-use Internet interface. (For many people, the Web is the Internet. But UNIX lets you do much more.)
A UNIX program that's been around for years, long before networking was common, is mail. It sends electronic memos, usually called email messages, between a user and one or more other users. When you send email, your message waits for the other user(s) to start their own mail program. The people who get your message can file it, print it, reply to it, forward it to other people, and much more. System programs can send you mail to tell you about problems or give you information. You can send mail to programs, to ask them for information. Worldwide mailing lists connect users into discussion groups.
There's more, of course. There are zillions of mail programs for UNIX-some standard, some from vendors, and many freely available. The more common email programs include mailx, Pine, mush, elm, and MH (a package made up of many utilties including comp, inc, show, and so on). Find one that's right for you and use it!
The ftp program is one way to transfer files between your computer and another computer with TCP/IP, often over the Internet network. ftp requires a username and password on the remote computer. Anonymous ftp (52.7) uses the ftp program and a special restricted account named anonymous on the remote computer. It's usually used for transferring freely available files and programs from central sites to users at many other computers.
UNIX-to-UNIX Copy is a family of programs (uucp (52.7), uux, uulog, and others) for transferring files and email between computers. UUCP is usually used with modems over telephone lines.
Usenet isn't exactly a network. It's a collection of thousands of computers worldwide that exchange files called news articles. This "net news" system has hundreds of interactive discussion groups, electronic bulletin boards, for discussing everything from technical topics to erotic art.
This utility logs you into a remote computer over a network (such as the Internet) using TCP/IP. You can work on the remote computer as if it were your local computer. The telnet program is available on many operating systems; telnet can log you into other operating systems from your UNIX host and vice versa. A special version of telnet called tn3270 will log into IBM mainframes.
Similar to telnet but mostly used between UNIX systems. Special setups, including a file named .rhosts in your remote home directory, let you log into the remote computer without typing your password.
A "remote cp" program for copying files between computers. It has the same command-line syntax as cp except that hostnames are added to the remote pathnames.
Starts a "remote shell" to run a command on a remote system without needing to log in interactively.
NFS isn't a user utility. The Network FileSystem and related packages like NIS (the Network Information Service) let your system administrator mount remote computers' filesystems onto your local computer. You can use the remote filesystem as easily as if it were on your local computer.
Sends messsages to another user's screen. Two users can have a discussion with write.
A more sophisticated program than write, talk splits the screen into two pieces and lets users type at the same time if they want to. talk can be used over networks, though not all versions of talk can talk to one another.
If you'd like more information, there are quite a few books about networking. Some Nutshell Handbooks on networking and communications include The Whole Internet User's Guide and Catalog - ail, Usenet, ftp, telnet, and more); Using Usenet; !%@:: The Directory of Electronic Mail Addressing & Networks; and many more advanced books for programming and administration.