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Bourne Shell: Chapter 8
Please contact
Dana French
or
Mt Xia
for assistance with all your shell programming needs.
8. ADVANCED FEATURES OF FTP.
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8. ADVANCED FEATURES OF FTP
This chapter will discuss some advanced features of the FTP server
as implemented on the Multimax. The introduction of FTP in UNIX
for Beginning Users gave an elementary introduction to some of the
features. If you are not familiar with the basics, please refer
to that manual. It is not the purpose to review those basics here.
The FTP (Internet file transfer program) is the user interface to
the DARPA File Transfer Protocol. This utility program will
transfer files to and from a remote computer. In order for files
to be transferred from the local computer to a remote computer, a
connection must be established. This can be done from the FTP
command line. The connection to the remote computer will remain
active until it is terminated by the user.
The remote computer with whom the connection is to be made can be
specified on the FTP command. In this case, FTP will immediately
try to establish a connection. If the remote computer is not
specified, FTP will enter its command interpreter mode and wait
for instructions; a prompt will be displayed.
FTP does have a help feature, and all 58 commands can be listed.
It will also give a terse description of each command. In
addition, there are on-line manual pages which can be accessed by
using the man command in UMAX.
8.1 Initializing FTP on UMAX
The term, "local computer," will refer to the Multimax. The
"remote computer" will refer to the other computer with which you
are trying to send/receive files. For purposes of this course, we
will be referring to the VAX minicomputer as the remote computer.
Please be aware that these procedures will work for any computer
connected to Ethernet and having an FTP server.
FTP can be invoked on the local computer using the following
syntax:
Command Format: ftp [-v] [-d] [-i] [-n] [-g] [host]
-v = verbose on, forces ftp to show all responses
from the remote server
-d = enables debugging
-i = turn off interactive prompting during
multiple file transfers.
-n = disables the "auto-login" feature
-g = disable filename globbing
host = the name of the remote computer
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NOTE: UMAX (UNIX) is case sensitive. The commands and options
must be entered as shown.
8.2 Multiple File Transfers
The syntax for the multiple get command is:
Command Format: mget remote-files
remote-files = remote computer wildcard specification
or
file1 file2 ... filen
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The remote computer wildcard specification is expanded in a process
called globbing. Once the globbing is complete, a get is performed
on each filename; and it is transferred to the local computer.
The filename is the same on both computers. You can specify the
filenames to be transferred separating them with spaces.
Example:
ftp>mget *.dat;*
This command will transfer all versions of the remote-files that
have the filename extension of .dat. If the option -i was
specified on the call to FTP, then the files will be transferred
automatically. If the option was not specified, FTP will prompt
you before transferring each file.
Sample Session:
ftp>mget *.dat
mget change_pass.dat;1?
The default is 'yes', pressing (Ret) will cause the file to be sent
to the local directory. If you don't want this file transferred,
enter n(Ret); you will then be prompted for the next file, if one
exists.
8.3 Auto Login Feature
It is possible to have the login procedure occur automatically.
To do this requires a file in your home directory called .netrc.
The .netrc file contains login and initialization information to
be used by the auto-login process. The following variables are
used and can be separated by spaces, tabs, or new lines.
machine name
This is the name of the remote computer. The auto-login process
will search the .netrc file for a machine variable that matches
the name of the remote computer on the ftp command or as an open
command argument. Once a match is found, the next variables are
also processed until the end of file or another machine variable
is encountered.
login name
This is the username on the remote system. If this variable is
present, the auto-login process will login to the remote computer
with the given username.
password string
This is the password to be used when logging in to the remote
system.
NOTE: If this variable is present in the .netrc file, ftp will
abort the auto-login process if the .netrc file is
readable by anyone but the user.
account string
This supplies an additional account password. If present, the
auto-login process will supply the string as an additional password
if required by the remote server.
macdef name
This defines a macro. This variable will function like the ftp
macdef command. A macro is defined with the specified name, its
contents begin with the next .netrc line and continue until a null
line (2 new line characters). If a macro named init is defined,
it will be executed as the last step of the auto-login process.
Sample Session:
$cat .netrc
machine erc830
login teacher
password secret1
machine erc780
login rharding
password secret2
$
To invoke the auto-login feature, type the ftp command and enter
the name of the remote computer as an argument.
Sample Session:
$ftp erc830
Connected to erc830.
220 erc830 Wollongong FTP Server (Ver 5.0) at Tue Oct 23
331 Password required for rharding.
230 User logged in, default directory D_1131:[RHARDING]
ftp>
If the .netrc file is readable by anyone other than the user, the
following error message will appear; and the connection will not
be made to the remote computer.
Sample Session:
$ls -l .netrc
$ftp erc830
Connected to erc830.
220 erc830 Wollongong FTP Server (Ver 5.0) at Tue Oct 23
Error - .netrc file not correct mode.
Remove password or correct code.
221 Goodbye.
ftp>
To correct this error, change the mode of the .netrc file so it is
not readable by other users or remove the password from the file.
This is to prevent your password from being read by an unauthorized
user.
8.4 Macros
Macros are a single instruction that a program replaces by several,
usually, more complex instructions. The ftp command to create a
macro definition is:
Command Format: macdef macro-name
macro-name - the name of the macro
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After the macdef command is given, all subsequent lines are stored
as a macro with the name macro_def. Consecutive newline characters
or carriage returns terminate the input mode into the macro. There
is a limit of 16 defined macros and a limit of 4096 characters in
all defined macros.
Sample Session:
ftp>macdef get_files
open erc780
get file_1
put result_2
close
ftp>
In this example, the four lines of the macro can be executed simply
be entering get_files at the ftp prompt. The macro will only exist
until the current ftp session is closed.
8.5 Filename Translation
Filename conventions differ from one computer to another, and FTP
will allow you to translate the name as it is transferred. One
way is to specify the name of the file as it is to exist on the
local computer. This is done by the argument on the put or get
command.
Command Format: put local-file [remote-file]
get remote-file [local-file]
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If you don't specify the remote-file (for the put command) or the
local-file (for the get command), the name will be the same on both
the local and remote computer. This can cause a problem if you are
not aware of it. There is an FTP command that will allow
the name to be translated automatically.
Command Format: nmap [inpattern outpattern]
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If no arguments are supplied, it will set or unset the filename
mapping mechanism. If arguments are specified, remote filenames
are mapped during mput (multiple file puts) and put (single file)
commands that are issued without a specified remote filename.
If arguments are specified, local filenames are mapped during mget
(multiple file gets) and get (single file) commands that are issued
without a specified local filename.
The mapping follows the pattern set by inpattern and outpattern.
Variable templating is done by including the sequences "$1",
"$2",...."$9 "in inpattern. All other characters are treated
literally and are used to determine the nmap inpattern variable
values.
For example, say the inpattern was $1.$2 and the remote filename
is mydata.data, $1 would have the value mydata and $2 would have
the value data. The outpattern determines the resulting mapped
filename. The sequences "$1", "$2",..."$9", are replaced by the
value resulting from the inpattern template. "$0" is replaced by
the original filename.
8.6 Aborting Transfers
Press the terminal interrupt key (usually Ctrl-C) to abort a file
transfer. The sending transfer will stop immediately. Receiving
transfers will be halted by FTP sending an ABOR command to the
remote server and discarding any further data that is received.
If the remote server doesn't support the ABOR protocol command the
ftp> prompt will not appear until the requested file has been sent.
8.7 More Remote Computer Commands
These commands can be useful when working with the directories on
the remote computer.
This FTP command will change the remote machine current working
directory to the parent of the current working directory.
Command Format: delete remote-file
remote-file name of the file to delete
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This FTP command will delete the specified file.
Command Format: mdelete [remote-files]
remote-files names of the files to delete
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This FTP command acts as a multiple delete. It will delete all
the specified files.
Command Format: mkdir directory-name
directory-name the name of the directory to be created
on the remote computer.
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This FTP command will create a directory on the remote computer.
Command Format: rmdir directory-name
directory-name the name of the directory on the remote
computer that will be removed.
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This FTP command will remove the specified directory.
NOTE: This command will not work with some remote servers.
Workshop 8
This workshop will reinforce your understanding of the ideas
presented in Chapter 9. Login to the Multimax using the username
and password given to you by the instructor. Each student is to
complete the entire workshop.
DESK EXERCISES (10 minutes)
1. What FTP command is used to transfer more than one file
at a time? What FTP command will give a prompt to you
before each file is retrieved? Suggestion: there are two
ways
2. What is the name of the file where the auto-login
variables are found? Extra credit: Why does this file
begin with a dot (.)?
3. How can the file in question the auto-login file be
protected from unauthorized reading?
4. What do the following FTP commands do?
cdup
delete (tough question)
mdelete (ditto)
mkdir
rmdir
COMPUTER EXERCISES (30 minutes)
5. Transfer all the files from on the VAX (erc830) to the
domax1. Use only one command and use wildcards. The
username and password for the VAX will be given to you
by the instructor.
6. Transfer the files from the VAX and this time translate
the names of the files as they are transferred.
7. Create an auto-login file for the erc830 and
then do an auto-login to the VAX.
8. Logout.
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