The Best Internet Programs/BESTINTERNET.bin/internet/lrn_inet/li_ftp.txt

Text File | 1994-10-05 | 14.4 KB | 361 lines

 ftp

ftp is the mla (multi-letter acronym) for File Transfer
Protocol, a very important part of the TCP/IP suite of
protocols.  It allows you to transfer any sort of file
from any of thousands of remote computer systems to your
own.  You can transfer executable computer programs,
grpahics, sound, video or any other sort of files from
remote archives to your own Internet host computer.

And it's all free.




 Which Way Is Up?

When you transfer a file from a remote computer to your own,
you say "I downloaded a file."  When you transfer from your
own computer to another one, you say "I uploaded a file."
Down = to you; Up = away from you.  These terms can be con-
fusing.

It is even more confusing when you dial in to the
Internet, because downloading will bring the file to your
Internet host computer, not to your home PC or MAC.   There
is another step involved in downloading the file once again
to your home computer.


 I Wish To Remain Anonymous

As with telnet, the restriction to using remote computers is
that you must have authorization to use them (an account,
a user ID and a password).  FTP gets around this problem by
allowing a service called "anonymous ftp."  That is, when you
connect to a remote computer that allows anonymous ftp you
enter your user ID as "anonymous."  When asked for a password
enter your full email address, eg: [e-mail].
Some systems verify your email address, some do not, but in
any event it is proper netiquette to provide it to the
remote host.



 Ye Be Properly Warned Says I

Two warnings about ftp.
   1) Once you see all the goodies you can get with ftp you
      are likely to go crazy and download way more than you
      can ever look at or use.  Practice restraint.  If you
      are working under a disk quota system (you probably
      are) you will rapidly exhaust your disk space alloca-
      tion, or exasperate the system administator, or both.

   2) Many ftp archives do not check their offerings for
      viruses.  Before running any ftped file scan it with a
      good, current virus checker.  The best one around is
      shareware from McAfee.  Ftp it from mcafee.com.

 ftp ftp

ftp allows access to the world's largest library--the library
of freely available computer files spanning thousands of
computers.  To start ftp type the command ftp followed by
the address of the host to which you wish to connect.

For example, ftp mcafee.com

Many ftp servers are set up separately on the Internet, so
their address looks like ftp.spies.com.  Therefore the com-
mand to connect to ftp.spies.com is: ftp ftp.spies.com.
This is confusing, but that's the way it is.


 Logging In To An ftp Host

When you make connections with an ftp host, the host will
ask for your name with a prompt like:

     Name(mcafee.com:efudd):

This is where you type "anonymous," even though the host
knows who you are.  When it asks for a password, enter your
full email address.  It will not echo the password to the
screen so type carefully.

Be sure to read the informational screen that appears next.
These screens are usually VERY important.

 The Rules Change

Once on an ftp host, the commands for file handling change
from the unix commands on your home computer.  To see a
listing of files in a certain directory enter: dir, not ls
as in unix.  To change to a certain subdirectory enter:
cd [name of subdirectory].  Subdirectory paths are separated
(as in Unix, but not in DOS) with forward slashes. For ex-
ample to change to the directory /pub/win3 enter: cd pub/win3.

If the file you want is a binary file (a computer program,
graphic, sound, or other non-text file) you must enter the
command image (or i for short) first.  You will see the
message File Type set to I.  This is critical.

 Getting Stuff

To get a file, enter the command get [filename].  To get a
group of files with similar names enter the command
mget [filename pattern].  For example, to get all the files
in a directory with the file extension .zip you would enter
the command: mget *.zip.  (Careful.  This would probably do
more than you think and download a ton of files).

Let's practice these concepts with a sample ftp session.  We
are going to simulate getting that antivirus program from
McAfee Associates mentioned above.

Press PgDn to log in and start the ftp session...

 Archie

The quantity of free software available via anonymous ftp is
truly vast, but if you don't know where a program is located,
how do you find it?  Answer: archie.  Archie is a program
that searches the "Internet Archive Database" (which is up-
dated about weekly).  It will look for exact or partial
matches to program names that you supply and report back to
you the program's location.  Then you can ftp to that site
and obtain the program.  Archie also has a whatis service,
which searches a much smaller database of program descrip-
tions.  Archie has been called the card catalog to the
largest library in the world.


 Using Archie

You begin by telnetting to a public archie server.  The
printed summary to this lesson has a list of them, as
does the resource section of this program.  Log in as
archie.  You will see the archie> prompt.  To see a summary
of available commands enter: help ?.

To use archie you must first set it up.  There are a
number of parameters that you should set--and different
archie servers use different defaults--so you need to check.
To see them enter the command: show.



 Archie Parameters

There are three types of archie parameters: boolean, numeric
and string.  (Don't let the weird terminology throw you!)
Boolean parameters will either be set or not.  The one you
care most about is one called "pager."  When pager is set, the
output of archie is delivered one screen at a time, using the
paging program called "less."  If pager is not set, and you
want it set, enter the command: set pager.  The numeric para-
meter you care most about is "maxhits."  It controls the
number of "hits" returned by the search.  It is usually set
to 100 when you begin.  You should set it to a smaller num-
ber, like 10.  Entering the command "set maxhits 10" is
what you should do.

 More Parameters

String parameters are parameters that have word values--
"string" is computerese for "word."  The two most important
are the "search" and "sortby" parameters.  You should set
the search parameter to "sub."  (Set search sub, is the
command).  This instructs archie to search for a partial
match to the search term you enter.  The other important
string parameter is the sortby parameter.  You can set it
to filename, hostname, size, date, time, or none, depending
on how you want to see your output.  If you are going to
be doing a lot of archie searching you should also set the
"mailto" parameter with your email address.  That way when
you issue the mail command you will not have to enter it.

 Searching

To search with archie issue the command: find [searchterm].
Different archie servers run different versions of the archie
software, however, and some do not recognize the "find"
command.  (It is newer).  If this is the case with the server
you are using use the "prog" command instead.  Archie was
originally designed to find programs only (thus "prog"), but
archie now searches for many types of documents in addition
to programs, so newer versions of the software have changed
the command to "find."  Once you have issued this command,
be prepared for a wait.  Archie servers are very busy and the
searches can take substantial time.  To break out of a search
before it is finished press Control-C.

 Output

If pager is set you can review your archie output one screen
at a time, browsing back and forth using the "less" program
commands.  (Less has numerous commands.  From archie you can
read about them by entering the command: man less, and then
mailing the results to yourself.)  The two less commands you
must know are: spacebar = show next page; q = quit.  Once
your output has been displayed you can mail it to yourself
by issuing the "mail" command.  If you have not set the
"mailto" parameter you will have to enter your email address
each time you issue the mail command.

Now that you know it all, let's practice...

 File Types

This lesson may seem particularly technical, but it is
unavoidably so.  If you are using ftp to get files from
archived sites, or downloading files from Usenet newsgroups,
you will come across a bewildering variety of archived,
compressed, zipped and encoded files.  To get the real
benefit of using the Internet you need to understand how
to work with these file types.  The aim of this lesson is
to clarify the difference between these vaious file types
and to tell you how to handle them.




 Compressed Files

A compressed file is one that has been squeezed to a smaller
size by use of a program that uses special compression algo-
rithms.  Why?  So that it will take up less space to store
and transfer the file.  Before it can be a useful file again,
however, it has to be unsqueezed and restored to normal.  So
for every compression program there is an uncompress program.
In fact two of the most common Unix utilities for squeezing
and unsqueezing files are called "compress" and "uncompress."
Other compression programs you need to know about are
gzip/gunzip, pkzip/pkunzip, and a utility called zcat, which
allows reading of compressed files before they are uncom-
pressed.  Gzip is for unix.  Pkzip for MS-DOS files.

 Archived Files

An archived file is a file made up of several other files all
strung together.  Many programs are actually not a single
file but a system of files including program, graphics,
data, and text files.  To store and keep track of so many
files is difficult, so they are archived together into a
single file for storage and transfer purposes.  In unix the
archiving utility is called "tar" (which means tape archive
program).  It's MS-DOS relative is the same pkzip mentioned
above.  pkzip both compresses AND archives.  Bear in mind
however, an archived file is not necessarily a compressed
file.  In fact the tar program does not perform compression.


 File Extensions

Because you can't tell from a superficial look at a file
whether it is compressed, archived, both or neither, certain
naming conventions have been established.  A cryptic "file
extension" (one or more letters following a period appended
to a file name) indicates what has been done to the file.
If a file has been archived with the unix tar program it has
a file extension of ".tar."  If it has been compressed with
the compress program it has a file extension of ".Z."  If
it has been compressed with the gzip program it has a file
extension of ".gz," unless it is specifically an MS-DOS file
in which case it has the extension of ".z."  If it has been
archived/compressed with pkzip it's extension is ".zip."

 Some Examples, Please

  filename.tar   - A group of files archived into one file
                   using the unix "tar" program.

  filename.Z     - A single file compressed using the unix
                   program "compress."

  filename.tar.Z - A file which was first a group of files
                   archived into a single file with "tar" and
                   then compressed with "compress."

  filename.zip   - A file compressed with the MS-DOS program
                   "pkzip."

 Archive (.tar) Files

To archive a group of files from the unix prompt enter the
following command:
     tar -cvf filename.tar file1 file2 file3 ...
Note the unix switches after the tar command.  The c means
"create" an archive, the v means report back "verbosely,"
and the f means the name of the archive is immediately
"following."  After the .tar file name enter the names of
the files to be archived, separated by spaces.

To unarchive a tar file, use this command:
   tar -xvf filename.tar
The x means "extract." Tar will not remove the original file.

 Compress (.Z) Files

To compress a file enter this command:
     compress filename
where filename is the name of the file you want compressed.
The results will be a file called: filename.Z.  The original
file will be removed.  To uncompress this file:
     uncompress filename.Z
The results will be an uncompressed file without the ".Z"
extension.  The original compressed file will be removed.

To read a .Z (or .gz) file before it is uncompressed use
the unix utility zcat if the file is a compressed text
file.  Zcat won't help if the file is a binary file.

 Archived Compressed Files (.tar.Z)

Files which have been both archived and compressed with the
unix "tar" and "compress" utilities will be called:
   filename.tar.Z (or .gz, if gzip was used).  MS-DOS files
are processed in this way using the pkzip program.  They have
a file extension of ".zip."

The unix programs tar and compress/uncompress are standard on
unix systems and you will have access to them if your host is
a unix computer.  Pkzip/pkunzip are MS-DOS programs distrib-
uted as shareware, like this program, which means you can get
it and use it free, and if you like it must send the author a
small fee.  You can get pkzip from most any ftp archive.

 Uuencoded Files

Usenet news and standard unix mail work only with text files,
so if you want to mail a binary file, or post a binary file
to a Usenet news group, you must first convert it to a text
file.  This is what the program uuencode does.  Uuencoded
files are often given the file extension ".uue."  To decode
the file on the other end use the unix program uudecode.
Uedecode does not remove the original encoded file from
your directory after decoding.

Another unix program that does the same job is "btoa" (binary
to ascii).  To go the other way use the command:
   btoa -a filename.

 Tarmail

Many unix installations offer a program that will archive,
compress, and mail (using standard unix mail's SMTP) a
set of files all with one command.  It is called "tarmail."
For example,
   tarmail [e-mail] 'This Is It' file1 file2 file3 ...
The part within the single quotes becomes the mail subject
line.  When you receive tarmailed mail first save it to a
file, and then issue the command: untarmail filename.

There is a great deal more that could be said about file
types, but your head is probably already spinning.  This
lesson's printed summary will help you further.