BBS in a Box 15/BBS in a box XV-1.iso/Files/Internet/Info/Internet Roadmap.sit/Internet Roadmap ƒ/Map 16 Ftp File Compression↵

Text File | 1995-02-14 | 12.2 KB | 300 lines | [ttro/ttxt]

MAP16: FTP FILE COMPRESSION
---------------------------

     "Travel is glamorous only in retrospect." -- Paul Theroux,
      quoted in The Observer


Own a personal computer for any amount of time, and you will quickly
realize that the amount of storage space on your computer is limited.
One way to deal with this problem is to use a compression software
package that "squishes" unused programs into small "boxes", thus
freeing up a little more of your disk space for other programs.

It turns out that storage space problems are not limited solely to
personal computers. As the numbers of files that are available
through ftp increases daily, ftp sites are actively looking
for ways to squeeze more files into a limited amount of space.

The ftp sites accomplish this by using file compression.

The good news is that a compressed file takes up a lot less space
on the ftp site's computer. The bad news is that a compressed file
is absolutely useless until you uncompress it.

Wait ... it gets worse. Before you can uncompress a file, you have
to know what compression method was used to compress the file in
the first place. Unfortunately, there is no one standard ftp file
compression method -- there are HUNDREDS of different file compression
methods in use today :(

If you have to know what compression method was used before you
can uncompress a file, how are you ever going to figure out which
method was used? Well, it is actually pretty easy:

     1. Most ftp directories have a READ.ME file that shows an
        index of all the files that are in that directory. Some
        really nice ftp sites have expanded READ.ME files that
        include a mention about what compression method was used
        and where you can get a free copy of the software needed
        to uncompress the files.

     2. Look at the files' extensions. By looking at the extensions
        and comparing them to the chart below, you will be able to
        determine what compression method was used and what particular
        software is needed to uncompress the file.

Fortunately, most uncompression software is either public domain (meaning
that it is completely free) or shareware (meaning that you can get a copy
of it for free, but the author expects you to send him some money for the
program if you decide to keep it and use it). Best of all, most
uncompression software is available through ftp! :)

The list below shows some of the most popular extensions that you
are bound to encounter during your visits to ftp sites around the
world. It also shows transfer modes needed to retrieve files with
these extensions, what uncompress software package you need to
to uncompress the files after you retrieve them, and it even gives
some additional comments about each of the extensions.

Paraphrasing something I said in MAP01, I want you to be aware
that the one compression method that isn't listed below is going
to be the one compression package that you ADORE. Please do not
take this personally. There are literally HUNDREDS of compression
methods in use today, and there is no way that I can list all
of them.

SUGGESTION: Save the following list, and use it as a reference tool
for when you encounter an extension that you have never seen before :)
Also, please notice that the following list talks about "archie".
Archie is an FTP search tool that we will discuss tomorrow.

-----

(the following list was adapted from "The EFF's Guide to the Internet"
by Patrick Crispen)

FILE           TRANSFER UNCOMPRESS
EXTENSION      MODE     PACKAGE      ADDITIONAL COMMENTS
------------   ------   ----------   -----------------------------------

.txt or .TXT   ASCII                 By itself, this means the file is
                                     a document rather than a program,
                                     and does not need to be uncompressed

.ps or .PS     ASCII                 A PostScript document (in Adobe's
                                     page description language). You can
                                     print this file on any PostScript
                                     capable printer or use a previewer,
                                     like GNU project's GhostScript.

.doc or .DOC   ASCII                 Another common extension for text
                                     documents. (Be careful, though: .doc
                                     and .DOC extensions are also used for
                                     Microsoft Word documents (which are
                                     Binary files). The duck theory will
                                     help you determine the difference)
                                     No decompression is needed, unless it
                                     is followed by:

.Z             Binary   uncompress   This indicates a Unix compression
                                     method. To uncompress type

                                          uncompress filename.Z

                                     and hit enter at your host system's
                                     command line.

                                     u16.zip is an MS-DOS program that
                                     will let you download .Z files and
                                     uncompress them on your own computer.
                                     The Macintosh equivalent program is
                                     called MacCompress (use archie to
                                     find these).

.zip or .ZIP   Binary   PKZip or     This indicates the file has been
                        Zip/Unzip    compressed with a common MS-DOS
                                     compression program, known as PKZIP
                                     (use archie to find PKZIP204.EXE).
                                     Many Unix systems will let you un-ZIP
                                     a file with a program called unzip.

.gz            Binary   gunzip       A Unix version of ZIP. To uncompress,
                                     type

                                          gunzip filename.gz

                                     at your host system's command line.

.zoo or .ZOO   Binary   zoo          A Unix and MS-DOS compression
                                     format. Use a program called zoo
                                     to uncompress.

.shar or .Shar Binary   unshar       Another Unix format. Use unshar
                                     to uncompress.

.tar           Binary   tar          Another Unix format, often used
                                     to compress several related files
                                     into one large file. All Unix
                                     systems will have a program called
                                     tar for "un-tarring" such files.
                                     Often, a "tarred" file will also be
                                     be compressed with the gz method,
                                     so you first have to use uncompress
                                     and then tar.

.sit or .Sit   Binary   StuffIt      A Macintosh format that requires
                                     the StuffIt program.

.ARC           Binary   ARC or       Another MS-DOS format, which
                        ARCE         requires the use of the ARC
                                     or ARCE programs.

.LHZ           Binary   LHARC        Another MS-DOS format; requires
                                     the use of LHARC.

"A few last words of caution: Check the size of a file before you get
it. The Net moves data at phenomenal rates of speed.  But that 500,000-
byte file that gets transferred to your host system in a few seconds
could take more than an hour or two to download to your computer if
you're using a 2400-baud modem.  Your host system may also have limits on
the amount of bytes you can store online at any one time.  Also, although
it is really extremely unlikely you will ever get a file infected with a
virus, if you plan to do much downloading over the Net, you'd be wise to
invest in a good anti-viral program, just in case." (1)


FTPMAIL AND BINARY FILES

Yesterday, I showed you that it is possible to get get ftp files
using e-mail by sending an e-mail letter to one of the following
addresses

          Australia      [e-mail]
          France         [e-mail]
          Germany        [e-mail]
          Great Britain  [e-mail]
          Ireland        [e-mail]
          Sweden         [e-mail]
          USA            [e-mail]
          USA            [e-mail]
          USA            [e-mail]

with the following commands in the body of your e-mail letter

          reply <your Internet address>
          connect <ftp site address>
          <transfer mode>
          chdir <directory>
          get <filename>
          quit

Before I introduce you to the new stuff, there are a couple of
things that I want to review with you.

First, the

          reply <your Internet address>

command tells the ftpmail address where you want the file sent.
If you use the example that I gave you yesterday

          reply [e-mail]
          connect ftp.sura.net
          ascii
          chdir /pub/articles
          get fall91.issue
          quit

without changing the reply address, ftpmail is going to send the
file to *ME*, not to you :)

Please remember to change the reply line to include *YOUR*
Internet e-mail address.

Also, I did not mention this yesterday, but ftpmail limits
you to only one CHDIR command per letter.

Finally, yesterday I asked you to contact you local Internet
service provider to see if they placed any size limits on
file transfers. If they do, there is an additional command
that you need to add to your list of commands

          chunksize <size>

This command will break the files into chunks that your
system can handle. If your system has a 50,000 character
limit on messages from the Internet, your chunksize
command should be

          chunksize 49000

(you want to make sure that you set your chunksize below what
your system's limits are). This command will break your file
into 49,000 character chunks, and will then send the chunks
to you :)

You already now how to retrieve ASCII text files using ftpmail.
Today, I am going to show you how to retrieve Binary files using
ftpmail.

Binary file transfers using ftpmail aren't difficult ... they
just require a few additional steps. Because all e-mail has to
be in ASCII form, ftpmail has to encode your Binary file in
ASCII before it can e-mail the file to you. Once you get the
file, you can then decode the file back into Binary :)

Fortunately, there are two ways that ftpmail can encode Binary
files into ASCII. The first way it can do this is through something
called "uuencode." As long as you have a uudecode program -- and
uudecode programs are all over the place (chances are your site
has uudecode stored on its system) -- the whole process is simple.

The second encoding type that you can use is called "btoa" (binary
to ascii). Your local Internet service provider will be able to
tell you a little more about btoa.

So, to get ASCII files using ftpmail, you would use the following
commands in the body of your letter to the ftpmail address:

          reply <your Internet address>
          connect <ftp site address>
          ascii
          chdir <directory>
          chunksize <size>
          get <filname>

and to get Binary files using ftpmail, you would use the following
commands in the body of your letter to the ftpmail address:

          reply <your Internet address>
          connect <ftp site address>
          <uuencode or btoa>
          chdir <directory>
          <encoding type>
          chunksize <size>
          get <filname>

TOMORROW: - ARCHIE
          - A *HUGE* LIST OF FTP SITES THAT YOU CAN VISIT

HOMEWORK

     Take a break. You've earned it :)


SOURCES

(1) "The EFF's Guide to the Internet", reprinted by permission.


   PATRICK DOUGLAS CRISPEN    THE VIEWS EXPRESSED IN THIS LETTER DO NOT
    [e-mail]      NECESSARILY REPRESENT THE VIEWS OF THE
  THE UNIVERSITY OF ALABAMA      UNIVERSITY OF ALABAMA - TUSCALOOSA

      ROADMAP: COPYRIGHT PATRICK CRISPEN 1994. ALL RIGHTS RESERVED.