Perl Script for uploading modified files to a FTP-Server

Introduction

(This article assumes that you are familar with Perl and ADO).

When uploading files from a local PC to a remote FTP-server, I ran into the problem of having to upload a lot of files, where only a few actually changed.

So I decided to compare the timestamps of the local files with those of the remote files. Theoretically a file needs to be uploaded only if

1. the local modification date is newer than the remote modification date or
2. the remote file doesn't exists at all.

In practice, the problem is that the FTP-Server has another timebase (e.g. its clock is some seconds ahed or behind the local clock), so the comparison could fail.

Upload Algorithm

The solution presented in this article handles this by storing the modification dates of the files to upload in a local database and does the comparison with these timestamps.

In a nutshell the "algorithm" works , for each file to upload, like this:

• Does an entry for the file exist in the database?
• If no, upload it, create new recordset for this file, storing its path and modification date.
• If yes, compare the actually modification date of the file with the stored modification date in the database.
• If actual modification date is newer than the stored one, upload the file, store its modification date in the database.
• If actual modification date is older than the stored one, do nothing.

As a drawback, the very first time the script is started, the database is empty, and therefore it once uploads all files, even if they would already exists on the remote FTP-server.

Starting from the second time, the script is executed, it works as described above.

Script installation

You must have installed the Windows version of Perl from ActiveState. I always use the latest version, which is ActivePerl 5.6 as of writing this article. 

In addition, I'm using some modules that are not in the standard distribution of Perl. These modules can be obtained from CPAN at www.cpan.org.

The following extra modules need to be installed:

• libnet (libnet-1.0703.tar.gz)
• TimeDate, (TimeDate-1.10.tar.gz)
• Date-Calc (Date-Calc-4.3.tar.gz) didn't work for me to install. Therefore I used the Date-Pcalc module (Date-Pcalc-1.1.tar.gz)

Each module contains a readme file which explains how to install.

Script configuration

When Perl and all modules are installed, you need to configure the script.

The following values must be configured:

Script execution

When you configured everything, simple execute the script by double-clicking it in the explorer or by typing "perl upload.pl" at the command prompt.

The script writes outpout to stdout, as well as to a logfile called "upload.log".

Epilog

If you have any suggestions, found errors or want to comment on that article or script, please write a comment to at the end of this article and I will answer it.

Please keep in mind that I'm doing Perl for only some few month right now. So there are probably a lot of "no really beautiful" code-fragments in my script. So if you have any constructive comments regarding my coding style or how the way I use Perl, please tell me!