Magazine article Online

The Internet Toolkit: File Compression and Archive Utilities

Magazine article Online

The Internet Toolkit: File Compression and Archive Utilities

Article excerpt

For the PC prospector looking for useful files, the Internet can be both an incredible resource and an extremely hostile place. Most computers that act as "anonymous FTP" file servers are running the UNIX operating system, and their directory displays look rather alien to a DOS user. Even after you figure out how to read a UNIX file display, discover that UNIX filenames are case-sensitive, and master commands for navigating the directory tree, you still may not be able to use the treasures that you find. There are lots of resources out there, but they aren't always useful immediately after downloading. Many files downloaded from the Internet require some type of "posttransfer" processing. Fortunately, there are several utility programs available for just that purpose.

FILE COMPRESSION

The speed of Internet connections is many times faster than most dial access connections. At the same time, the size of the typical file on the Internet may be significantly large than those found on dial-up bulletin board systems (BBS). As a result, you will find that many files available on the Internet have been processed with a compression utility, to make them smaller and thus faster to transmit.

You will frequently encounter two compression formats:

* files ending in "ZIP," which have been compressed with Phil Katz' PKZIP program, and,

* files ending in ".z," which have been compressed with a UNIX compression program.

To use these files after you have downloaded them, you must have the corresponding decompression programs.

PKUNZIP

Readers who use dial-up bulletin board systems probably already are familiar with the PKZIP program. Virtually all PC bulletin board systems use this shareware utility to compress files so that they download faster, and to "archive" one or more files together and store them in a single file. In this way, a software program and its documentation file can be combined into one downloadable package. Much of the MS-DOS freeware, shareware, and public domain software that is available on the Internet has been processed with the PKZIP program. Many other files on the Internet can be found in "ZIP" format: electronic documents such as resource guides, back issues of journals, and bibliographies; databases; graphic image files; etc. After such a file is downloaded, it must be "unzipped" with the companion PKUNZIP.EXE program, which decompresses the enclosed files and restores them to usable format.

Both ZIP programs are usually found in an archive file called PKZnnnn.EXE, where nnnn is the version number of the program. At the time of this writing, the current version number is 2.04g, with a filename PKZ204G.EXE. This is a "self-extracting" file--when executed by typing the filename, the program extracts and writes to disk both the PKZIP and PKUNZIP programs, as well as several other files. The original archive file is left intact, so that you can extract the files again later if needed. You can use PKZIP.EXE to create your own archives. Other included programs can repair damaged archive files, and let you create "self-extracting" files as well.

The basic usage of the PKUNZIP program is: pkunzip , as in pkunzip ejournal.zip.

Including the ".ZIP" filename extension in the command is optional. As the program works it will decompress each file in the archive and write it to disk. The original ".ZIP" file is left intact. If you want the extracted files stored in a directory other than the current one, you can specify it on the command line. For example, using pkunzip libguide.zip c:[unkeyable] download [unkeyable] texts, will store extracted files from the file libguide.zip in the given directory.

COMPRESS

On Internet FTP servers, files that have been processed with a UNIX compression utility are even more common that those processed with PKZIP. These files usually have filenames ending in ". …

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