[ UNIX ] [ WINDOWS ] [ FTP CLIENT DOCUMENTATION ] [ KERMIT SCRIPT LIBRARY ]
CLICK HERE to read about new FTP features in C-Kermit 8.0.206 Beta.
This page is written for users of Unix operating systems -- Linux, FreeBSD, AIX, HP-UX, IRIX, Solaris, etc. The Kermit FTP client is also available in Kermit 95 2.0 for Windows 9x/ME/NT/2000/XP, for which some of the applications, examples, and terminology used here might need minor adjustments (e.g. directory path syntax).Hardly a day goes by without an FTP automation question appearing in the newsgroups. Until now, the stock answers (for Unix) have been as follows (the options for Windows are sparse indeed):Also see: Accessing IBM Information Exchange with Kermit for a discussion of making securely authenticated and encrypted FTP connections.
Now there's a new alternative. The latest generation of Kermit software:
includes its own built-in FTP client, allowing FTP sessions to be automated using the same cross-platform, medium-independent scripting language we've been using for serial-port, modem, Telnet, and X.25 connections since the 1980s, in its advanced modern form:
http://www.columbia.edu/kermit/ck80specs.html#scripts
and has loads of features that you won't find in the regular UNIX FTP client:
http://www.columbia.edu/kermit/ftpclient.html
Here's a brief tutorial on writing C-Kermit FTP scripts. But the commands presented below are not just for scripts. You can also use them interactively, just as you would give commands to the regular UNIX or Windows FTP client, except that with Kermit you also get built-in help, context-sensitive help (if you type "?"), command recall, keyword and filename menus and completion, keyword abbreviation, and command shortcuts and macros.
#!/usr/local/bin/kermit + ftp open ftp.xyzcorp.com /anonymous if fail exit 1 Connection failed if not \v(ftp_loggedin) exit 1 Login failed ftp cd drivers if fail exit 1 ftp cd drivers: \v(ftp_message) cd ~/download if fail exit 1 cd ~/download: \v(errstring) ftp get /binary newdrivers.zip if fail exit 1 ftp get newdrivers.zip: \v(ftp_message) ftp bye exit
Here's a brief explanation, line by line:
http://www.columbia.edu/kermit/ckscripts.html
Let's say our script has been saved in a file called getnewdrivers. How to execute it? There are at least three ways:
In cases 1 and 2, the Kerbang line is not needed. Method 3 requires the getnewdrivers file to be in your PATH and that the Kerbang line of the script indicates the pathname of the C-Kermit 8.0 executable, and that the script file has execute permission:
chmod +x getnewdrivers
ftp open ftp.xyzcorp.com /user:olga /password:bigsecret
The rest of the script is the same, except perhaps now a full pathname is needed in the FTP CD command.
But it's a notoriously bad idea to put passwords in scripts or any other files (if this is news to you, please take it on faith). So how can the script log in as a real user without knowing the password in advance? There are lots of ways. The first is simply to have the script prompt for the password when it runs:
ftp open ftp.xyzcorp.com /user:olga
Just omit the /PASSWORD switch from the FTP OPEN command and Kermit prompts you for the password at the time it's needed (if it is), and you can supply it from your keyboard (it won't echo).
Alternatively, you can have Kermit prompt you for the password in advance. This might be appropriate when it's a long-running script and the FTP step doesn't happen until much later:
undefine \%p
while not defined \%p {
askq \%p Password:
}
....
ftp open ftp.xyzcorp.com /user:olga /password:\%p
if fail exit 1 Connection failed
undefine \%p ; Erase password from memory
Here you see some "programming": variables and loops. We ask the user to type in the password using Kermit's ASKQ command ("ask quietly", i.e. don't echo the response). Since a password is required, the WHILE loop makes Kermit keep asking until it gets one, at which time it is assigned to the variable \%p. Then when the FTP OPEN command is given, \%p is specified as the password. Since \%p is a variable, it is replaced by its definition, which is whatever the user typed. (Normally, everything in Kermit that starts with a backslash indicates some kind of replacement -- a variable, a function call, the numeric representation of a character, etc.)
As a security precaution, the second "undefine \%p" command erases the password from memory immediately after it is used, like the comment says (trailing comments in Kermit are set off from the command by a colon or number-sign surrounded by whitespace).
Now suppose you want your script to run unattended when nobody is there to type in the password. This is a classic problem. One solution is to start the script early, type the password, and then have the script wait until the the desired time to do its work, using Kermit's SLEEP command, e.g.:
sleep 6000 ; Sleep 6000 seconds sleep 23:59:59 ; Sleep until just before midnight
But what if you want the script to run periodically as a cron job, in which case there isn't even a terminal at which to type in the password? Well, that's a tough one, and it's one of the reasons for the appearance of secure FTP servers and Kermit's features for taking advantage of them. But that's another story, covered elsewhere:
http://www.columbia.edu/kermit/security.html
For example, if your version of C-Kermit was built with SSL/TLS security, and the server also supports SSL/TLS security, it is negotiated automatically. Various special commands can be used, but the only one that's required is SET AUTHENTICATION TLS VERIFY-FILE filename, that tells Kermit where to find the certificate file to be used to authenticate the FTP server.
#!/usr/local/bin/kermit + if < \v(argc) 3 exit 1 Usage: \%0 host file ftp open \%1 /anonymous if fail exit 1 \%1: Connection failed if not \v(ftp_loggedin) exit 1 Login failed cd ~/download if fail exit 1 cd ~/download: \v(errstring) ftp get /binary \%2: if fail exit 1 ftp get \%2: \v(ftp_message) ftp bye exit
Here we have simply replaced the host and file names by variables, /%1 and /%2, whose values are set automatically by Kermit from the command-line arguments. These are similar to the $1 and $2 Shell variables.
Let's call this version of the script getfile, since it's not just getting new drivers any more; you can use it to get any file from any host that accepts anonymous logins. \v(argc) is a built-in variable that says how many "arguments" there were on the command line, including the name of the script itself.
Assuming getfile is installed as a Kerbang script in your PATH, now you can give commands such as these at the shell prompt (or in a shell script):
getfile support.scsicorp.com drivers/scsidrivers.zip getfile kermit.columbia.edu kermit/archives/ckermit.tar.gz
If you run getfile without supplying the parameters it needs (host name and file name), it prints a usage message and exits with a failure code.
The command line arguments are passed to the script as:
\%0 The name of the script
\%1 The first command-line argument
\%2 The second command-line argument
Of course you can have more than 2 command-line arguments.
if not defined \%1 define \%1 ftp.xyzcorp.com if not defined \%2 define \%2 newdrivers.zip
The second way:
while not defined \%1 {
ask \%1 { Host: }
}
while not defined \%2 {
ask \%2 { File: }
}
Or a combination:
if not defined \%1 ask \%1 { Host [ftp.xyzcorp.com]: }
if not defined \%1 define \%1 ftp.xyzcorp.com
if not defined \%2 ask \%2 { File [newdrivers.zip]: }
if not defined \%2 define \%2 newdrivers.zip
A simple form of transaction processing is done by moving files from one computer to another, for example insurance claims from a pharmacy or doctor's office (the client site) to an insurance clearinghouse (the central site). A "watcher" process at the central site waits for files to appear in a certain directory and then processes them. In this case we want to make sure that each file is transferred completely and correctly, and exactly once, and furthermore:
In a Kermit protocol client/server setting, all of this is handled quite nicely by Kermit's "atomic file movement" features. Unfortunately, not all of these features are available in FTP protocol, most notably a way to tell the FTP server to move or rename each incoming file automatically after it has fully arrived. However, we can accomplish the same thing with a Kermit FTP client script.
In this scenario, each client site has its own login ID on the central site to prevent file collisions between different clients, and also to provide an authenticated association between the uploaded files and the clients themselves. Each client ID at the central site has two subdirectories, working and ready. Client files (orders, votes, reservations, insurance claims, whatever) are uploaded to the working directory and then moved to the ready directory when the upload is complete. The move is "atomic" -- when the file appears in the ready directory, it appears all at once, not bit by bit; thus it is truly ready for processing the instant it is visible. The central-site "watcher" process periodically looks for files to appear in each client's ready directory, and when one does appear, moves it again, this time to its own area, and processes it. Thus any files in the client's ready directory are waiting to be processed and should not be disturbed. It is the client's responsibility to ensure that each file is sent completely, and sent only once, and that it is not disturbed after it is sent.
Our script expects the name of the file to send as its first command-line argument. We begin our script by checking the argument:
#!/usr/local/bin/kermit + if not defined \%1 exit 1 Usage: \%0 filename if not exist \%1 exit 1 \%1: File not found if not readable \%1 exit 1 \%1: File not readable
Then we make the connection in the usual way:
undefine \%p
while not defined \%p {
askq \%p Password:
}
ftp open centralsite.com /user:clientid /password:\%p
if fail exit 1 Connection failed
if not \v(ftp_loggedin) exit 1 Login failed
undefine \%p
ftp cd working
if fail exit 1 ftp cd working: \v(ftp_message)
cd ~/upload
if fail exit 1 cd ~/upload: \v(errstring)
Now we upload the file:
ftp put /delete \%1 if fail exit 1 ftp put \%1: \v(ftp_message)
Notice that failure leaves the partial file (if any) in the working directory, where the central-site watcher process does not look for it. Thus transient failures do no harm. The script can be run again later. The /DELETE switch on the PUT command removes the source file after, and only if, it was uploaded successfully; this prevents it from being uploaded again (you could also have it moved or renamed). This way, even if the script is run again for the same file, it will fail immediately because the file is no longer there. Or, if a file of the same name is in the same place, it is a new file that should be uploaded.
Now we can move the uploaded file from the server's working directory to its ready directory (the syntax assumes a UNIX-like file system on server):
ftp rename \fbasename(\%1) ../ready/\fbasename(\%1) if fail exit 1 ftp rename \fbasename(\%1): \v(ftp_message)
The \fbasename() function strips any directory path from the filename, in case one was given (since the path is also stripped when sending the file's name to the FTP server).
But wait, what if the destination file already exists in the server's ready directory? This would indicate that a previous transaction with the same name had not yet been processed. We should allow for this possibility:
Here is the final version of our script:
#!/usr/local/bin/kermit +
; Veryify command-line parameter (name of file to send)
;
if not defined \%1 exit 1 Usage: \%0 filename
if not exist \%1 exit 1 \%1: File not found
if not readable \%1 exit 1 \%1: File not readable
; Prompt for server password
;
undefine \%p
while not defined \%p {
askq \%p Password:
}
; Open the connection and log in
;
ftp open centralsite.com /user:clientid /password:\%p
if fail exit 1 Connection failed
if not \v(ftp_loggedin) exit 1 Login failed
undefine \%p
; Check if file of same name already exists on the server
;
ftp cd ready
if fail exit 1 ftp cd ready: \v(ftp_message)
cd ~/upload
if fail exit 1 cd ~/upload: \v(errstring)
ftp check \%1
if success exit 1 \%1: Already exists in central site ready directory.
; OK to send - cd to server's working directory.
;
ftp cdup
if fail exit 1 ftp cdup: \v(ftp_message)
ftp cd working
if fail exit 1 ftp cd working: \v(ftp_message)
; Now we upload the file and delete local copy if successful.
;
ftp put /delete \%1
if fail exit 1 ftp put \%1: \v(ftp_message)
; Move the uploaded copy to the ready directory
;
ftp rename \fbasename(\%1) ../ready/\fbasename(\%1)
if fail exit 1 ftp rename \fbasename(\%1): \v(ftp_message)
bye
exit 0
Call the script file upload, make sure the Kerbang line indicates the C-Kermit 8.0 path, give it execute permission, and then run it from the shell prompt as:
$ upload claim01.dat
If it didn't succeed, the error message will tell you why and you can take corrective action and run it again. If you run it again without taking corrective action, no harm is done -- either it will work or it will fail. If it works and you run it again on the same file, it will fail harmlessly because the original file is gone.
C-Kermit 8.0 also includes GET and PUT options (switches) to rename server files after successful transfer, whose use could shorten our transaction processing script, and are especially useful when transferring multiple files in a single operation: [M]GET or [M]PUT /SERVER-RENAME:template. Read more about this in the documentation.
ftp put /after:-5days *
Notice there is nothing about text or binary mode in the command. That's because Kermit automatically switches into the appropriate mode for each file that it sends.
Or suppose you want to send all the files that are larger than one million bytes and whose names start with 'c' or 'w' except if the file's name is core or its name ends with .log:
ftp put /except:{{core}{*.log}} /larger:1000000 [cw]*
Or suppose you want to send all the files in an entire directory tree, which can include any combination of text and binary files, and have the same directory tree replicated on the FTP server, even if it is on a different operating system:
ftp put /recursive *
Now suppose that later, you want to refresh the same directory tree by uploading only those files that changed since last time:
ftp put /recursive /update *
Suppose you want to send a text file written in (say) German to another computer that uses a different character set:
ftp put /local-character-set:cp437 /server-character-set:latin1 Grüße.txt
Or suppose you want to continue uploading a very long file after a previous upload attempt was interrupted in the middle:
ftp put /recover verylong.tar.gz
Or suppose you want to synchronize a local directory from a remote one, even when you keep getting cut off, no matter how many tries it takes, without transferring any file that does not need to be updated, without transferring any file more than once, and without retransmitting any part of a file that was already partially received:
mkdir somelocaldirectory
cd somelocaldirectory
while true {
ftp open foo.bar.com /user:myname /password:secret
if fail exit 1 Can't reach host
if not \v(ftp_loggedin) exit 1 FTP login failed
ftp cd blah/blah/somepath
if fail exit 1 Directory change failed
while true {
ftp get /recover /update *
if success goto done
if not \v(ftp_connected) break
}
ftp bye
}
:done
Or suppose you want to . . .
All of this, and lots more, is easy to do with the Kermit FTP client, and it all can be automated.