In reply to John Williams question about compressed files...

The area of file compression and archiving is confusing, so I thought
I'd post a short summary for those having trouble.  This list is not
comprehensive!  I won't say much about Mac systems, except to say
that Alladin's excellent Stuffit and Stuffit lite are more or less
the universal standard - Mac users don't need any help..:-)

Most problems are due to different operating systems and formats.

Compressed files can either be single files or multi-file archives.

Single file compression

1.  UNIX compress
Found in some archive, especially older ones.  Proprietary protocol,
thus now used less widely .  Not recommended because of cross-platform
troubles.

File subscript:   .Z  (upper case - see gzip below)
Create with:     compress (UNIX or alternative OS implementation)
Extract with:    uncompress (UNIX or alternative OS implementation)
                         gunzip (see below)
Available:        On UNIX systems, etc.  plus proprietary things like
the MKS utilities for DOS

2  gzip/gunzip
The GNU alternative to compress.  Originally a UNIX-based programme, now
available on virtually every platform.  Probably the file compressor
of choice.  Can extract UNIX compress (.Z) files.  Freely available
under the GNU license.  Unfortunate name though - confusion with
pkzip (see below)., which is an archiver.

File subscript:   .gz  (lower case -now used universally)
                          .z  (lower case -dropped to avoid confusion
                                 with .Z)
Create with:     gzip
Extract with:   gunzip (or " gzip -d" - see documentation)
Available:        from a GNU site near you.  Make sure you get the
                         right version for your OS

Macgzip is also available


Archives
1.  Stuffit for Macs (lucky people)

2.  pkzip, etc.
Proprietary archiver/compressor.  Most PC users know about this one.
Can hold one or more files.

File subscript:   .zip
Create with:    pkzip
Extract with:   pkunzip
                       unzip (shareware)
                       ......etc.  - there are several others
                      Winzip etc. under Windows provide nice
                       interfaces and facilities (shareware)
Available:      PKware is widely available for purchase
                      extractors are very widely available

NOTE: self extracting archives can be created; these are .exe files

3.  UNIX tar
The original UNIX Tape ARchiver - does not compress, but allows files
(and directory structures) to be placed in single file which may then
be compressed.  Not really of much interest to PC users, but you will
find tar archives around - they usually mean the stuff in there is
from a UNIX source.  However, many programme source files (C, C++,
etc) are held in such archives, so may be of interest to some.

File subscript:   .tar (often .tar.Z or .tar.gz when compressed)
Create with:    tar (tar -cf  if you must ask) (or gtar)
Extract with:   tar (tar -xf........)  (or gtar)
Available:       tar is on every UNIX system
                       gtar is the GNU version, available from GNU
                        sites/mirrors

WARNING: tar archives are (usually) created under UNIX.  This
supports long file names and multiple occurances of periods (.) in
filenames.  The directory separator is a forward slash (/).  If you
try to extract a tar archive under DOS/Windows, the system won't like
it.  OS/2 tar (under HPFS) manages OK.

There are other systems, including ZOO (.zoo suffix) and ARC (.arc).
Not widely used now.


A word of warning:  some sites, for instance DEMON, don't always
hold the latest versions of software like GNU,  so it worthwhile going
to the original site or a mirror that aims to keep up to date. That's
why I use sites like LEO, despite it being slow (OS/2 only, I'm
afraid - sorry I can't suggest good Windows mirrors)

Hope this is of help


>>>>>>>>>>>>>>>>>>>>>>
Andrzej Glowinski
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