Encyclopedia of Computer Science and Technology

428 shellPC-Write as a full-featured alternative to expensive commercialword processing program. Because Fluegelman hadtrademarked the term freeware, these other authors beganto call their offerings shareware.Today freeware means software that can be downloadedat no cost and for which there is no charge for continueduse. The program may be redistributed by users as long asthey don’t charge for it.Shareware, on the other hand, follows Fluegelman’soriginal concept. The software can be downloaded for free.The user is allowed to try the program for a limited period(either a length of time such as 30 days, or a maximumnumber of times that the program can be run). After thetrial period, the user is expected to pay the author thespecified fee of continued use. (Today this is usually donethrough the author’s Web site or a service that can acceptsecure credit card payments online.) Once the user pays,he or she receives either an unrestricted version of the softwareor frequently, an alphanumeric key that can be typedinto the program to remove all restrictions. At this pointthe program is said to be “registered.”Users can be encouraged (or forced) to pay in variousways. Some programs keep working after the trial period,but display continual “nag” messages or remove some functionality,such as the ability to print or save one’s work.(“Demos” of commercial games or other programs also havelimited functionality, but cannot be registered or upgraded.They are there simply to entice consumers to buy the commercialproduct.)Alternatively, some shareware authors prefer to enticetheir users to register by offering bonuses, such as additionalfeatures, free upgrades, or additional technical support.Sometimes (as with the RealPlayer streaming soundand video player and the Eudora e-mail program) a usefulbut limited “lite” version is offered as freeware, but usersare encouraged to upgrade to a more full-featured “professional”version.Shareware has been a moderately successful businessfor a number of program authors. For example, Phil Katz’sPKZip file compression and packaging program is so usefulthat it has found its way onto millions of PCs, and enoughusers paid for the program to keep Katz in business. (PKZipand its cousin WinZip are examples of shareware programsthat became so popular that they spawned commerciallypackaged versions.)Shareware and freeware should be distinguished frompublic domain and open source software (see open-sourcemovement). Public domain software is not only free (aswith freeware), but the author has given up all rights includingcopyright, and users are free to alter the program’s codeor to use it as part of a new program. Open-source software,on the other hand, allows users free access to the softwareand its source code, but with certain restrictions—notably,that it not be used in some other product for which accesswill be restricted.Today tens of thousands of shareware and freeware programsare available on the Internet via ftp archives, author’sWeb sites, and giant online libraries maintained by zdnet.com, cnet.com, tucows.com, and others.Further ReadingAssociation of Shareware Professionals. Available online. URL:http://www.asp-shareware.org. Accessed August 21, 2007.Ellis, Robert. Handpicked Software for Mac OS X: The Best NewFreeware, Shareware, and Commercial Software for Mac OS X.Petaluma, Calif.: Futurosity, 2002.Hasted, Edward. Software That Sells: A Practical Guide to Developingand Marketing Your Software Project. Indianapolis: Wiley, 2005.Lehnert, Wendy G. The Web Wizard’s Guide to Freeware and Shareware.Boston: Addison-Wesley, 2002.Shareware.com. Available online. URL: http://www.shareware.com. Accessed August 21, 2007.Tucows.com. Available online. URL: http://www.tucows.com.Accessed August 21, 2007.shellDuring the 1950s, using a computer generally meant thatoperators submitted batch-processing command cards (seejob control language) that controlled how each programwould use the computer’s resources. One programran at a time, and interaction with the user was minimal.However, when time-sharing computers began to appearin the 1960s, users gained the ability to control the computerinteractively from terminals. The operating systemtherefore needed to have a facility that would interpret andexecute the commands being typed in by the users, such asa request to list the files in a directory or to send a file to theprinter. This command interpreter is called a shell.To see a simple shell in action, a Windows user needonly bring up a command prompt, type the word dir, andpress Enter. A shell called command.com provides the userinterface for users of IBM PC-compatible systems runningMS-DOS. The command processor displays a prompt onthe screen. It then interprets (see parsing) the user’s commands.If the command involves one of the shell’s internaloperations (such as “dir” to list a file directory), it simplyexecutes that routine. For example the command:dir temp /pwould be interpreted as a call to execute the dir function,passing it the name “temp” (a directory) and the /p, which dirinterprets as a “switch” or instruction telling it to pause thedirectory listing after each screenful of text. If the commandis an external MS-DOS utility such as “xcopy” (a file copyingprogram), the shell runs that program, passing it the information(mainly file names) from the command line. Finally,the shell can run any other executable program on the system.It is then that program’s responsibility to interpret andact upon any additional information that was provided.MS-DOS also has the ability for the command.com shell toread a series of commands stored in a text file called a batchfile, and having the *.bat (batch) extension. This allowed forrudimentary scripting of system housekeeping operations orother routine tasks (see scripting languages).UNIX ShellsMS-DOS largely faded away in the 1990s as more usersswitched to Microsoft Windows and begun to use a graphicaluser interface to control their machines. However, shells