Chapter 5

FILE TRANSFER PROTOCOL (ftp)


This is a very important service available on the Internet. The file transfer protocol (ftp) gives you the ability to retrieve and store files to and from a distant computer. Many computers on the Internet allow login with the username "anonymous" and your E-mail address as the password. While nowadays, the availability of "gopher" or the World Wide Web (Lynx and graphical WEB) make this somewhat redundant, it is good to know how file transfer happens, even if in your application it occurs in the background and is not directly visible to you. There are a large number of files still stored on ftp sites.

Hundreds of systems connected to the Internet have file libraries and archives accessible to the public. Much of this consists of free or low-cost shareware programs for virtually every make of computer. For example, if you want a different communications program for your IBM, or feel like playing a new game on your Amiga, you'll be able to get it from the Net, with ftp.

There are libraries of documents as well. If you want a copy of a recent U.S. Supreme Court decision, you can find it on the Net. Copies of historical documents, from the Magna Carta to the Declaration of Independence, are yours for the asking, along with a translation of a telegram from Lenin ordering the execution of rebellious peasants. You can find song lyrics, poems, even text summaries of every "Lost in Space" episode ever made. You can find extensive files detailing everything you could ever possibly want to know about the Net itself.

First you'll see how to get these files, then we'll show you where they are kept.

5.1 Using ftp

Starting ftp is easy. Fig.5-1 shows the first step, which is to go to the First Menu and select item 2, FTP. This opens the application program called FTP on the VSNL computer, and gives you the " ftp> " prompt.

Fig.5-1 Opening FTP

At the "ftp>" prompt, type "open site.name", as indicated below,

ftp> open site.name

and press <enter>, where "site.name" is the address of the ftp site where you hope to get the file you want.

One major difference between telnet and ftp is that it is considered bad form to connect to most ftp sites during their business hours (generally 6 a.m. to 6 p.m. local time). This is because transferring files across the network blocks up considerable communication resources, which during the day is likely to be needed for whatever the computer's main function is. There are some ftp sites that are accessible to the public 24 hours a day.

The first question is how to locate your desired information or file on the multitude of Internet sites or host computers. There are three approaches to the answer:

• Word-of-mouth. A friend tells you what file is available from which computer.
• Going to ftp sites, browsing, and reading the "readme" files which give one-line
• descriptions of the files.
• Using an Internet tool called "archie", described later in this chapter.

5.2 Browsing an anonymous ftp site

Supposing you know the site where the file you want is stored, what is the procedure to get the file? This question is answered by showing you a transcript of an ftp session, step by step. Let us assume you have found out that your desired file may be on the sites "ftp.cica.indiana.edu" or "oak.oakland.edu". Thus at the ftp> prompt, you should enter the first address.

Fig.5-2 shows your entry at the ftp prompt, and following that, the responses received from the ftp site, and your further entries at subsequent ftp> prompts:

Fig.5-2 Response from an ftp site

You may find useful information on this site. Therefore, you decide to log on to the site. Fig.5-3 shows information and instructions which are given by the site after you have logged on.

Fig.5-3 Information from an ftp site you have logged on to.

Your entry at the last ftp> prompt, shown in Fig.5-3, was to go to the sub-directory named simtel, indicated in the third last line of the listing, above. This name is usually given to the directory which holds the shareware software. The ftp session transcript continues in Fig. 5-4.

Fig.5-4 Contents of the SimTel directory on the ftp site.

Let's decipher this:

The ftp command for displaying a directory is either "ls - l" or "dir". It is advisable to keep in mind that only "ls - l" works on your own host system.

The very first letter on each line tells you whether the listing is for a directory or a file. If the first letter is a "d" or an "l", it's a directory. Otherwise, it's a file.

The rest of that weird set of letters and dashes consist of "flags" that tell the ftp site who can look at, change or delete the file. You can safely ignore it. You can also ignore the rest of the line until you get to the second number, the one just before the date. This tells you how large the file is, in bytes. If the line is for a directory or sub-directory, the number gives you a rough indication of how many items are in that directory -- a directory listing of 512 bytes is relatively small. Next comes the date the file or directory was uploaded, followed (finally!) by its name.

Notice the README. files up at the top of the directory. Most archive sites have a "read me" document, which usually contains some basic information about the site, its resources and how to use them. How to read a file at an ftp site will be discussed in detail later.

Let us assume you want the MS-DOS versions of the files. Therefore, you change to the msdos directory by typing "cd msdos" at the ftp prompt as shown below:

ftp> cd msdos

This takes you to the directory which holds msdos files and sub-directories, as shown in Fig.5-5.

Fig.5-5 Contents of msdos directory.

Subsequently, you can type the "ls - l" command at the "ftp" prompt, as shown below, to see the directory contents as shown in Fig.5-6 and Fig.5-7:

ftp> ls-l

Fig.5-6 Response to "ls-l" command

What we have got in Fig.5-6 is a partial alphabetical listing of subdirectories that contain programs. After removing many subdirectories which were listed, the remaining listing is shown in Fig.5-7.

Fig.5-7 Continuation of the "ls-l" command response

As you can see, there are a large number of sub-directories in the msdos directory. You can pick the area of your interest and scan the directory to determine the file you may want to download. As mentioned earlier, there is usually a readme file in the directory, giving one-line descriptions for each item, for your guidance.

ftp> bye

221 Goodbye.

So, now you know how to log on to an ftp site, maneuver yourself to different directories, and get a directory listing. We have yet to do something useful once we are there.

5.3 Reading a text file at an ftp site

Ftp can only transfer files, not read their content, so you would normally have to wait until you have transferred the file to your account at VSNL, in order to see what is in it. However, there is a little-known trick to read a file without leaving the ftp site, by giving the command "get README | more" at the "ftp>" prompt, as shown below.

ftp> get README |more

This will display the contents of the text file page by page on your screen. It is very important to be able to do this. To go to the next page, press spacebar.

5.4 Getting a file to your account at VSNL

Now you are ready to transfer a file from the remote server to your account. To accomplish this you have to decide if the file is a text file or a binary (computer program, coded e.g. MSWord, or any compressed) file as you need to use the appropriate method for each type of file. For a simple text file, the transfer command will be:

ftp> get filename

For a computer program, the transfer command is:

ftp> bin

Press <Enter> after the transfer command. This tells the ftp site and your host site that you are sending a binary file, i.e., a program. Most ftp sites now use binary format as a default, but it's a good idea to use this, in case you've connected to one of the few that doesn't.

Then issue the command to get the file:

ftp> get filename

The file will now be transferred to your account at VSNL. To get it to your computer, you will need to do a file download, a topic discussed in Chapters 11 & 13.

Suppose you want to transfer the file from your account to another computer. The command for this is "put filename", given after the "ftp>" prompt, which is the reverse of the get command and functions exactly like it.

There are other important commands which are used quite frequently. These are listed in the second column of Table below, and the resulting action is given in the first column.

Table. of frequently-used ftp commands

Of course there are many more commands but the above-mentioned ones are used most often, by most of us.

5.5 Odd letters - Decoding file endings

Files are commonly stored in compressed form. There are a wide variety of compression methods in use, and most of these decompression programs can be located through "archie". You can tell which method was used by the last one to three letters at the end of a file name. Here are some of the more common ones, with instructions regarding how to un-compress the respective file.

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 the 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, or if your telephone connection to VSNL is so poor that the modem speed gets adjusted down to 1200 baud for example. Your host system may also have limits on the amount of bytes you are allowed to store online, at any one time. Furthermore, although it is 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.

5.6 Your friend 'archie'

How do you find a file you want, though?

Until a few years ago, this could be quite a pain -- there was no master directory to tell you where a given file might be stored on the Net. Who'd want to slog through hundreds of file libraries looking for something?

Alan Emtage, Bill Heelan and Peter Deutsch, students at McGill University in Montreal, asked the same question. Unlike the others, though, they did something about it. They created a database system, called 'archie', that periodically calls up file libraries and basically finds out what they have available. In turn, anybody can dial into archie, type in a file name, and see where on the Net it is available. Archie currently catalogs some 1,000 file libraries around the world.

Today, there are three avenues to ask archie to find a file for you:

Telnet,

A "client" Archie program on your own host system, or

• E-mail.

All three methods let you type in a full or partial file name and will tell you where on the Net it's stored.

If you have access to telnet, you can telnet to one of the following addresses:

archie.mcgill.ca

archie.sura.net

archie.unl.edu

archie.ans.net

archie.rutgers.edu

If asked for a log-in name, type

archie

and press <Enter>.

When you connect, the key command is prog, which you use in this form:

prog filename

followed by <enter>, where "filename" is the program or file you're looking for. If you're unsure of a file's complete name, try typing in part of the name. For example, "PKZ" will work if you are searching for "PKZG204.EXE." The system does not support DOS or Unix wildcards (asterisks in place of parts of a filename). You can use archie to search for, say, everything online related to the Beatles, as well as computer programs and graphics files.

archie -s filename |more

will stop the output every screen (handy if there are many sites that carry the file you want). Or you could open a file on your computer with your text-logging function.

Fig.5-8 shows a transcript of an online session at VSNL to search for the file pkzip.exe: From the first Main Menu make a selection of item "3", telnet service and proceed as follows:

Fig. 5-8 Opening a archie session

The following are the results of the search by "archie". As the total number of sites is very large, we are listing only a representative sample in Fig.5-9:

Fig.5-9

The third way, for people without access to either of the above, is e-mail. Send a message to

archie@quiche.cs.mcgill.ca

You can leave the subject line blank. Inside the message, type

prog filename

where filename is the file you're looking for. You can ask archie to look up several programs by putting their names on the same "prog" line, like this:

prog file1 file2 file3

Within a few hours, archie will write back with a list of the appropriate sites.

In all three cases, if there is a system that has your file, you'll get a response that looks something like this:

Host sumex-aim.stanford.edu

Location: /info-mac/comm

FILE -rw-r--r-- 258256 Feb 15 17:07 zterm-09.hqx

Location: /info-mac/misc

FILE -rw-r--r-- 7490 Sep 12 1991 zterm-sys7-color-icons.hqx

Chances are, you will get a number of similar looking responses for each program. The "Host" is the system that has the file. The "Location" tells you which directory to look in when you connect to that system. Ignore the funny-looking collections of r's and hyphens for now, as they have something to do with file permissions. After these comes the size of the file or directory listing in bytes, the date it was uploaded or updated, and the name of the file.

a) Archie sites accessible by Telnet:

The following are few of the Archie servers that you can access using telnet. Please use the username

archie

to login, use server closest to you:

To start an archie search using an archie server that you have telnetted to, type

find <searchterm>

replacing <searchterm> with what you want the server to search for (see example above).

After Archie has finished its search and printed its results on your screen, you can have Archie e-mail the results to you by typing:

mail <your Internet address>

replacing <your Internet address> with our full e-mail address. To quit the telnet session type quit at the prompt.

b) Accessing Archie By e-mail

You can conduct archie search by e-mail. To do so send an e-mail to the Archie server closest to you:

Archie mail address Location

archie@archie.au Australia
archie@archie.advz.uni-linz.ac.at Austria
archie@archie.univie.ac.at Austria
archie@archie.uqam.ca Canada
archie@archie.mcgill.ca Canada
archie@archie.funet.fi Finland
archie@archie.univ-rennes1.fr France
archie@archie.th.darmstadt.de Germany
archie@archie.ac.il Israel
archie@archie.unipi.it Italy
archie@archie.wide.ad.jp Japan
archie@archie.hana.nm.kr Korea
archie@archie.sogang.ac.kr Korea
archie@archie.uninett.no Norway
archie@archie.rediris.es Spain
archie@archie.luth.se Sweden
archie@archie.switch.ch Switzerland
archie@archie.ncu.edu.tw Taiwan
archie@archie.doc.ic.ac.uk United Kingdom
archie@archie.hensa.ac.uk United Kingdom
archie@archie.unl.edu USA(NE)
archie@archie.internic.net USA(NJ)
archie@archie.rutgers.edu USA(NJ)
archie@archie.ans.net USA(NY)
archie@archie.sura.net USA(MD)

Top of the Chapter
Chapter 4 Using E-mail (Electronic Mail)
Chapter 6 TELNET
Table of Contents