rfc1635.txt

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   compression, bundling, and transformation conventions used on the
   Internet.  This list is not intended to be exhaustive.  In all cases
   public domain or freely-available implementations of the programs
   associated with these mechanisms are available on the network.

     1) compress/uncompress

     Filenames terminating in ".Z" normally signify files that have been
     compressed by the standard UNIX Lempel-Ziv "compress" utility.
     There is an equivalent program called "uncompress" to reverse the
     process and return the file to its original state.  No bundling
     mechanism is provided, and the resulting files are always in binary
     format, regardless of the original format of the input data.

     2) atob/btoa

     Performs a transformation of ASCII to binary (atob) and the reverse
     (btoa) in a standard format.  Files so transformed often have
     filenames terminated with ".atob".  No bundling or compression
     mechanisms are used.







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     3) atox/xtoa

     A data transformation standard used to convert binary
     files to transferable ASCII format.  Sometimes used in
     preference to other similar mechanisms because it is more
     space efficient; however, it is not a compression
     mechanism per se.  It is just more efficient in the
     transformation from one format to the other.  Filenames of
     files in this format often have the ".atox" extension.

     4) uuencode/uudecode

     Transforms binary to ASCII ("uuencode") and the reverse
     ("uudecode") transformation in a standard manner.
     Originally used in the UUCP ("Unix to Unix CoPy")
     mail/USENET system.  No bundling or compression mechanisms
     are used.  Naming conventions often add a .uu at the end
     of the file name.

     5) tar/untar

     Originally a UNIX based utility for bundling (and
     unbundling) several files and directories into (and from)
     a single file (the acronym stands for "Tape ARchive").
     Standard format provides no compression mechanism.  The
     resulting bundled file is always in binary format
     regardless of whether the constituent files are binary or
     not.  Naming conventions usually hold that the filename of
     a "tarfile" contain the sequence ".tar" or "-tar".

     6) zip/unzip

     Often used in IBM PC environments, these complementary programs
     provide both bundling and compression mechanisms.  The resulting
     files are always in binary format.  Files resulting from the "zip"
     program are by convention terminated with the ".zip" filename
     extension.

     7) arc/unarc

     Often used in IBM PC environments, these complementary programs
     provide both bundling and compression mechanisms.  The resulting
     files are always in binary format.  Files stored in this format
     often have a ".arc" filename extension.







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     8) binhex

     Used in the Apple MacIntosh environment, the binhex
     process provides bundling as well as binary to ASCII data
     transformations.  Files in this format by convention have
     a filename extension of ".hqx".

     9) shar

     Bourse shell archives package text or binary files into a
     single longer file which, when executed, will create the
     component files.  Because this format is vulnerable to
     misuse, most users use a special tool called unshar to
     decode these archives.  By convention, files in this
     format have a filename extension of ".shar".

     10) VMS_SHARE

     DCL archives package text or binary files into a single
     longer file which, when executed, will created the
     component files.  Because this format is vulnerable to
     misuse, care must be take to examine such an archive
     before executing it.  By convention, files in this format
     have a filename extension of ".shar".

     11) Multipart shar/vms_share files

     Sometimes these shell archive files are broken into
     multiple small parts to simplify their transfer over other
     forms of fileservers that share the same archive tree.  In
     such cases, the parts of the files are usually suffixed
     with a part number (e.g., xyz.01 xyz.02 xyz.03 ... or even
     .01-of-05).  Collect all the parts, concatenate them on
     your local system, and then apply the procedure listed
     above for a simple shar or vms_share file to the
     concatenated file you just made.

     12) zoo

     The zoo program implements compression/decompression and
     bundling/unbundling in a single program.  Utilities
     supporting the zoo format exist on a wide variety of
     systems, including Unix, MS-DOS, Macintosh, OS/2, Atari
     ST, and VAX VMS.  Files created by the "zoo" programs by
     convention end with the ".zoo" filename extension.  Zoo is
     a popular distribution format due to the availability of
     free implementations (both source and executable code) on
     a wide variety of operating systems.



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     13) gzip/gunzip

     The Free Software Foundation GNU project adopted a variant
     of the zip compression mechanism as a substitute for the
     compress/uncompress commands.  The resulting files are
     always in binary format.  Files resulting from the "gzip"
     program are by convention terminated with the ".z" or
     ".gz" filename extensions.  The gunzip program also
     recognizes ".tgz" and ".taz" as shorthands for ".tar.z" or
     ".tar.Z".  Also, gunzip can recognize and decompress files
     created by the gzip, zip, compress, or pack commands.

     The GNU project recently began distributing and using the
     gzip/gunzip utilities.  Even more recently they changed
     the default suffix from .z to .gz, in an attempt to (1)
     reduce confusion with .Z, and (2) eliminate a problem with
     case-insensitive file systems such as MS-DOS.  The gzip
     software is freely redistributable and has been ported to
     most UNIX systems, as well as Amiga, Atari, MSDOS, OS2,
     and VMS systems.

   In some cases, a series of the above processes are performed to
   produce the final file as stored on the archive.  In cases where
   multiple transformation processes have been used, tradition holds
   that the original (base) filename be changed to reflect these
   processes, and that the associated filename extensions be added in
   the order in which the processes were performed.  For example, a
   common procedure is first to bundle the original files and
   directories using the "tar" process, then to "compress" the bundled
   file.  Starting with a base file name of "foobar", the file name in
   the archive would become "foobar.tar.Z".  As this is a binary file,
   it would require a further transformation into printable ASCII by a
   program such as "uuencode" in order to be transmitted over
   traditional email or USENET facilities, so it might finally be called
   "foobar.tar.Z.uu."

   Some operating systems can not handle multiple periods; in such cases
   they are often replaced by hyphen ( - ), underscore ( _ ), or by
   detailed instructions in the "read me" files in the directories.

Compress and Tar

   Here is an example of the use of the "compress/uncompress" and
   "tar/untar" programs.

   Suppose "patch" is a useful public domain program for applying
   program patches and updates.  You find this file at an archive site
   as "patch.tar.Z".  Now you know that the ".Z" indicates that the file



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   was compressed with the UNIX "compress" command, and the ".tar"
   indicates that it was tar'ed using the UNIX "tar" tape archive
   command.

   First retrieve the file onto your machine using anonymous FTP.  To
   unpack this program, you would first  uncompress it by typing:

      uncompress patch.tar.Z

   This will uncompress the file, and in the process, rename it to
   "patch.tar".  You can then execute the "tar" command to extract the
   individual files.

   In the example of patch.tar, you could invoke the command as:

      %tar xvf patch.tar

   The files would be extracted (that's the 'x' argument to tar) from
   the file patch.tar (that's the 'f' argument).  Because we use the 'v'
   (for verbose) argument, the name of each file is printed as it is
   extracted.  When tar is complete you should have all the files that
   make up the "patch" program in your working directory.

Etiquette

   Not every site that supports FTP permits anonymous tranfers.  It is
   wrong to try to get files from systems that have not advertised the
   availability of such a service.

   Remember that Internet site administrators for archive sites have
   made their systems available out of a sense of community.  Rarely are
   they fully compensated for the time and effort it takes to administer
   such a site.  There are some things users can do to make their jobs
   somewhat easier, such as checking with local support personnel first
   if problems occur before asking the archive administrator for help.

   Most archive machines perform other functions as well.  Please
   respect the needs of their primary users and restrict your FTP access
   to non-prime hours (generally between 1900 and 0600 hours local time
   for that site) whenever possible.  It is especially important to
   remember this for sites located on another continent or across a
   significant body of water because most such links are relatively slow
   and heavily loaded.








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   In addition, some sites offering anonymous FTP limit the number of
   concurrent anonymous FTP logins.  If your attempt to log onto such a
   site results in an error message to the effect that too many
   anonymous FTP users are online, you should wait a while before
   attempting another connection rather than retrying immediately.

   To reduce redundant storage, you should find out how to make useful
   the files you fetch using FTP available to your entire organization.
   If you retrieve and test a program that turns out to be useful, you
   should probably ask your administrator to consider making the program
   generally available, which will reduce the redundant effort and disk
   space resulting from multiple individuals installing the same package
   in their personal directories.

   If you find an interesting file or program on an archive site, tell
   others about it.  You should not copy the file or program to your own
   archive unless you are willing to keep your copy current.

References

   [1] Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)", STD
       9, RFC 959, USC/Information Sciences Institute, October 1985.

Security Considerations

   Security issues are not discussed in this memo.

























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Authors' Addresses

   Peter Deutsch
   Bunyip Information Systems
   266 Blvd. Neptune
   Dorval, Quebec, H9S 2L4
   Canada

   Phone: [phone]
   EMail: [e-mail]


   Alan Emtage
   Bunyip Information Systems
   266 Blvd. Neptune
   Dorval, Quebec, H9S 2L4
   Canada

   Phone: [phone]
   EMail: [e-mail]


   April N. Marine
   NASA NAIC
   M/S 204-14
   Ames Research Center
   Moffett Field, CA 94035-1000

   Phone: [phone]
   EMail: [e-mail]





















IAFA Working Group                                             [Page 13]