how to install rpm file in debian.i downloaded vsftpd.rpm to install ftp server

This really isn't a Perl related question.. now isn't it?

It would be nice if you monks could help me in this matter

Nice and appropriate are often two different things. Why don't you try joining the Linux mailing list (one of many) over on Yahoo Groups or post to one of the Linux related newsgroups. I'm sure you'll find someone to help you there.

#! /usr/bin/perl

use strict;
use warnings;

system("apt-get install vsftp"); # Note I don't actually know if this 
+is the correct syntax for apt-get as I usually use the evil RHEL

[download]

Use the perl script alien, which can convert various non-debian packages to debian format. Oh, okay, it can also convert .debs to lesser formats as well.

# alien some_stupid_package.rpm
[download]

Firstly, as others have said, your question is completely off-topic for this site.

Secondly, whilst it's possible to install rpms on Debian, that's not Debian's native packaging mechanism. Debian uses .deb files and apt. You would make your life much easier if you looked for a Debian .deb version of vsftpd. And there seems to be one available from the Debian web site.