Dealing with compressed/archived files

Some of the information is provided by anonymous ftp servers around the world, and such files are marked with [ftp]. Accessing such files can occasionally cause problems as they are usually compressed and some are archives, so a few terms are explained here. Sources of programs to perform de-compression/de-archiving are also given, but please be aware that these are only an example. The locations of these programs may move over time and of course newer improved versions will appear.

Anonymous ftp is provided by the TCP/IP ftp service where you normally user a userid of anonymous and for a password give your email address. This is done automatically for you when you acces the file via the web page. However if your server does not provide ftp access you may get "permission denied". If you do have problems, it is always worthwhile trying to access the file via ftp rather than www. The URL will give you the name of the machine to contact and the file to access.
Compressed files. The large files provided via anonymous ftp are usually compressed to speed the transfer. These files should always be transferred in binary if using the ftp command. Some www servers cannot handle compressed files, and if so you should try ftp instead. You may also need to uncompress the file after transfer if your server can't handle that particular compression algorithm. The type of compression is usually determined by the suffix on the filename. E.g.

.zip
The DOS pkzip format. The usual DOS utility to uncompress them is pkunzip, and on Unix its usually unzip. Both programs are freely available.
.Z
The Unix compress program created them,. Use uncompress to undo them.
.tar
A Unix tar archive. Use tar xf to extract the files from it.
.tar.Z
A compressed tar file. Uncompress then use tar xf ...
.z or .gz
A gziped file. Use gzip -d to uncompress it.
.tgz
A gziped tar file.

Uncompressing *.Z files in MSDOS

If you are using an MSDOS system you will need comp430d.exe to uncompress the *.Z files. This is a public domain program that can be obtained by anonymous FTP from:

Location: oak.oakland.edu Directory: SimTel/msdos/compress File: comp430d.zip

Put it in a directory accesable from your Path and unzip it. Then, as the accompanying documentation says, "the best thing to do is to copy it to compress.exe, uncompre.exe and zcat.exe.... To uncompress a *.Z file, simply type uncompress *.Z"

Uncompressing *.zip files in MSDOS

If you need an unzipper, you can get the latest version of pkzip (2.04g) from:

Location: oak.oakland.edu Directory: pub/msdos/zip File: pkz204g.exe

This is shareware, free for non-commercial use. Put it in a directory accesable from your path. To unzip a *.zip file, type pkunzip filname (the .zip extension is optional).

Reference: Useful MSDOS Programs at SIMTEL20 and Garbo (Part 1 of 2) by Samuel Ko (kko@sfu.ca) 30 March 1993. This is regularly posted to a number of Internet news groups including news.answers.

Untaring *.tar files in MSDOS

This is an optional step, I find it more convenient to load the uncompressed file into a word processor and use it there. If you do this you will see occasional blocks of strange characters (mainly 'y') which are an artifact of taring - just ignore them.

If you do want to untar, use tar.exe. This is a public domain program that can be obtained by anonymous FTP from:

Location: ftp.cso.uiuc.edu Directory: pc/exec-pc File: tar.zip

Put it in a directory accessable from your Path and unzip it. Unzipping produces a lot of files. You only need tar.exe, tar.1 and tar.5 (the last two are documentation) - the others can be deleted.

The commands to use are:

tar tf xxx.tar
Lists archived files
tar xf xxx.tar
Untars them
tar xvf xxx.tar
Untars them and tells you what it's doing

If it finds a file that it can't easily convert to a DOS file name (eg 1851.Lin.Lec.01) it will prompt you for a replacement. On my system just typing a reasonable file name followed by Return dosen't work. If you experience this problem, try typing a reasonable file name *followed by Ctrl Z* then Return.

Uncompresing and unarchiving on the Apple Mac

Binhex, Zip, UUencode, etc., on Apple Macintosh computers.

On Apple Macintosh computers, running System 7.0 or later, what is currently probably the easiest way of dealing with many if not all of file encodings and compression schemes in common use is to use StuffIt Expander together with DropStuff with Expander Enhancer.

StuffIt Expander expands archives from the archive-based compression formats: StuffItT and Compact ProT, or which have been "encoded" in BinHex 4.0 format.

With DropStuff with Expander Enhancer installed, StuffIt Expander is also able to decompress files that were compressed on Unix systems and IBM-PCs and compatibles, including ZIP (.zip), and ARC (.arc) archives; AppleLink (.pkg) packages; gzip (.gz), Unix Compress (.Z), UUencoded (.uu), and StuffIt SpaceSaver files.

To decompress or decode a file when you have both these programs installed you can use Drag & Drop, i.e.:

In the Finder, select the icon of the relevant file.
Drag it over the StuffIt Expander icon until it is highlighted.
Let go of the mouse/trackball button.

StuffIt Expander will open and you will see a progress dialog. When everything is decompressed or decoded, StuffIt Expander automatically quits, leaving the resulting converted file alongside the original file.

Alternatively your Web browser may well have a facility by means of which you can arrange that it automatically invokes StuffIt Expander as a "helper application" - how this is set up depends on the particular browser you are using.

Both of these programs are copyright, Aladdin Systems, Inc., 165 Westridge Drive, Watsonville, CA 95076, USA (email: aladdin@well.com).

Stuffit Expander is Freeware, but DropStuff with Expander Enhancer is Shareware. You may use DropStuff with Expander for up to 15 days, after which a shareware fee of $30 is due.

Both programs are available on many standard Mac archives.

"tar" archives on Apple Macintosh computers.

Amongst the various means of dealing with file archives in the UNIX "tar" format (obtained via binary ftp) one of the easiest is to use Suntar. With Macs running System 7.0 or later one can use drag & drop to launch the program and open the "tar" archive, so that one can then select which files are to be extracted.

Suntar is freeware developed by Sauro & Gabriele Speranza, via Cappuccini 18, 40026 Imola, Italy (email: speranza@cirfid.unibo.it)

The program is available on many standard Mac archives.

Further help on decompression

A very comprehensive document on 'cross-platform' compression/archiving utilites is available from <ftp://ftp.cso.uiuc.edu/pub/doc/pcnet/compression>