Because DOS has been available for so long and has been used on so many computer systems over the years, several utility programs that run under DOS and can accomplish various useful tasks are available. Many of these utilities are available either free or as shareware programs that you can evaluate free and then pay to license if you decide to keep them.

In this chapter, you learn about several such powerful utility programs for DOS; they can help you accomplish more with a DOS-based computer system or even make better use of the DOS command prompt in Windows and OS/2. The following DOS-based utility programs are covered in this chapter:

Using these programs, you can increase your capability to manage files under DOS; to remain free of computer viruses; to create, manage, and extract compressed file archives; and to make the best use of the DOS command prompt.

Programmers write computer programs for many reasons: for fun, for profit, as demonstrations, as self-educational projects, or to solve some computing problem that they have noticed. However, not every program has the commercial appeal of, say, an Intuit Quicken or a Microsoft Word.

Sometimes programmers choose to make their programs available to others free. When they do so, it is understood that the programs are available on an as is basis with no warranty and no support from the programmers if some kind of problem occurs. If the program does something useful for you, that's great. If it doesn't, at least it didn't cost you anything. Note that programs distributed free—often called freeware—usually still carry restrictions that you cannot modify the program in any way and that the programmer's original copyright must be left intact. You are typically also free to give copies to others, although you need to examine each program's copyright notice for details because they vary from program to program.

Some software programmers often choose to sell their creations using an electronic version of a “word of mouth” sales approach called shareware. In this model, people are free to download and try the software for a limited period of time (usually 30 days or so); and then, if they choose to keep the software, they pay the programmer a reasonable license fee. Users are encouraged to pass along shareware programs they like to other people, who also must pay to license the software if they want to keep it. The basic idea is to make software available for sale with much lower selling and distribution costs than traditional software, with both the programmer and user benefiting from the more efficient transaction: The programmer makes more money on each copy sold, and the user pays much less for useful software. Shareware programs are typically sold with some sort of warranty, with support from the maker, and often with other benefits such as free upgrades to newer versions that become available. Note that all these benefits usually accrue only to buyers of the software, not to those who are simply evaluating the programs.

Another form of program is sometimes called demoware. With demoware, the software has been modified so that certain key functions do not work. For instance, a demonstration of a program that generates reports might print only one page of its reports or might print all pages with a prominent notice that the software is unlicensed. (Sometimes software like this is uncharitably called crippleware because key functions are deliberately crippled.) Usually, after a user has paid for a license, the crippled functions are restored, or a properly functioning version of the program is sent to the buyer.

The third-party utilities described in this chapter are, for the most part, shareware. All their functions work properly, although continued use requires that you pay for a copy of the program. The nice thing is that all these utilities are very powerful and useful, easy to get, and inexpensive to purchase if you want to continue using them.

PKZIP and PKUNZIP are programs that can create and read special archive files. These archive files are called Zip files, and they invariably end with the .ZIP file extension. Zip files are special archive files that contain compressed copies of one or more normal files. Because of the compression that takes place for Zip files, Zip files are usually many times smaller than the original files themselves. The PKZIP program creates Zip files, whereas the PKUNZIP program reads files from within a Zip file and places copies on your disk. Two other programs included as part of the shareware version of PKZIP are described in Table 22.1.

The PKZIP programs are essential for almost any computer user. They enable you to accomplish many important tasks that you cannot otherwise accomplish with DOS alone, such as the following:

McAfee VirusScan is one of the most widely distributed shareware programs in existence. McAfee VirusScan can rapidly scan your computer for viruses, even looking inside documents for macro viruses.

McAfee VirusScan is downloaded as a single Zip file that, when extracted using PKUNZIP, results in a main program file and a number of support files. The main program file is called either SCAN.EXE or SCANPM.EXE, depending on which of two possible DOS versions you are using. In a pure DOS environment, you use SCAN.EXE. SCANPM.EXE, on the other hand, is a DOS version intended for use with protected-mode versions of DOS, such as the DOS built into Windows 98 or OS/2.

To run a simple scan of a disk drive using VirusScan, type the program name (SCAN or SCANPM), followed by the drive letter to be scanned. The scan starts immediately, and any detected viruses are reported to you, along with a prompt asking whether you want to repair or delete the infected file.

Unless you use your computer disconnected from all other computers, using only your own documents and prepackaged software, you need to regularly scan your system for computer viruses. They are unfortunately common these days, and they can sit dormant on your system for years until the right circumstances trigger them. When triggered, they can wreak havoc on your computer's programs and data, and can require professional assistance for removal—in addition to possibly causing loss of data. Aside from regularly scanning your system for viruses with a program such as McAfee VirusScan, you also need to make regular backups of your important data, which can help protect you from data loss, regardless of whether it is caused by a computer virus or something else.

Quite possibly the best utility program for DOS discussed in this chapter is a program called 4DOS, which actually serves to improve upon DOS in virtually every way conceivable. 4DOS is from a company called JP Software, and it replaces DOS's COMMAND.COM with a much more competent version that contains many powerful features not found in MS-DOS or any other DOS. Versions of 4DOS that can run under Windows 9x/ME, Windows NT/2000, and OS/2 also are available.

4DOS doesn't change the behavior of any of the DOS commands you have already learned, but it does add more features to all of them. For instance, the DIR command still works in the same way in 4DOS, but it also accepts a larger number of parameters that enable you to format its output much more flexibly than you can with the DIR command in standard DOS. Furthermore, the TYPE command, which cannot accept wildcards or multiple filenames under DOS, easily does so with 4DOS. Table 22.2 shows the major improvements that 4DOS makes to existing DOS commands.

In addition to extending the functionality of DOS commands, 4DOS adds new commands not available in DOS. For example, you might have been frustrated by the CD command's incapability to change disk drives along with directories. 4DOS contains a command called CDD that enables you to do just that. Or perhaps you have wished for a timed pause for batch files instead of DOS's simple PAUSE command, which waits for a key to be pressed. 4DOS adds a command called DELAY that pauses a batch file for a specified number of seconds. Table 22.3 shows important new commands available in 4DOS that are not generally included with DOS.

Another powerful feature of 4DOS is extended batch file capabilities, including a built-in batch file debugger that enables you to step through batch files and more easily solve problems within them. Add to this the capability to use BTM files that run much more quickly than standard BAT files, along with the powerful batch file commands available in 4DOS, and you can see that you can do much, much more with 4DOS batch files than with DOS batch files.

If you really want to become a DOS wizard, adding 4DOS to your bag of tricks can take you very far, indeed. The nice thing about 4DOS is that you can start using it without knowing much about it because DOS commands still work the same way. As you come across situations in which you wish DOS had some additional feature, you can open the 4DOS help file and see whether it helps you solve a particular problem. Chances are excellent that 4DOS can help you accomplish many tasks you want to perform in DOS.