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Automation (1)

Programmers should always try to be as lazy as they can. This post will explain several tricks used to retrieve automatically some password protected zipped file on a ftp server in an automated way.

Connection to the ftp server

Basically, the difficulty will be to establih a connection without entering the password.  The thing is just to write (or modifiy) a parameter file called .netrc in your home directory.

This file is a simple text file protected by permissions  set to 600 (chmod 600 .netrc).

It will contain for each (ftp) server you will be connected to, three lines :

  1. a name of the server (or ip address)
  2. a login
  3. a password

Once your .netrc is set, in order to connect to the server myftp.server.com, you ‘ll only have to write the following command in a terminal.

ftp myftp.server.com

And you ‘ll be automatically connected !

Retrieving the data

In an interactive ftp session , you would have to write basic command on the server to change directory and get data. In an automated script, you’ll have to write all this command in a text file and pass the later to ftp client.

So if we must move to the directory Mydir1 and get the file “file1”, we’ll have to create a file with the following instructions :

cat >ftp.in<<EOF
 open myftp.server.com
 cd Mydir1
 get file1.zip

and then execute :

ftp <ftp.in

Or in a more straight forward way :

ftp -i<<EOF
 open myftp.server.com
 cd Mydir1
 get file1.zip

Possible difficulties :

If we know that the name of the directory will change, let’s say Mydir1 can change to Mydir2, we may use in our script before submission a variable.

If the file name change is unpredictable (let says there is a suffixe giving the creation date in ddmmyyhhmmss) you’ll have no other choice than using mget instead of get. mget accept to retrieve file matching a pattern expressed with meta caracters.

Our script will become :

cat >ftp <<EOF
open myftp.server.com
cd Mydir$num
mget file*.zip


Now that the file is downloaded, we’ll have to unzip it, which can been done with the following command :

for fic in  file*.zip
unzip -P "PassWord" $fic

Putting all the later instructions in a shell script file allow me to spare some time (unfortunately this time has also been automaticaly used to work on another task…poor me !)

Categories: Linux, Shell
  1. AL
    December 19, 2011 at 10:38 am
  2. December 19, 2011 at 10:43 am

    😉 Touché !

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