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Perl Tutorial

Perl is a an extremely popular server-side scripting language, which uses the Common Gateway Interface (CGI) to produce dynamic content and allow for client-server interaction. Originally developed by Larry Wall, Perl is the end product of many contributors worldwide.

Perl scripts are commonly found throughout the web development community. As with any programming script, Perl has its benefits and disadvantages. Some benefits of Perl include the fact that it is easy to learn, commonly accepted as a scripting language, so there is much support and examples on Perl, plus there is a lot of documentation. Additionally, Perl can handle regular expressions much better and more efficiently that most other programming languages. However, as a scripting language, Perl must be interpreted when called, so it is usually slower than other alternatives. Scripts are open-source, so there is a greater vulnerability to the programmer.

Perl scripts are plentysome on the web, many of which are free. Below are some excellent resources for Perl scripts:

Matt's Script Archive, Inc.
CGI-Resources

These Perl archives have over 1,000 Perl scripts for you to use, authored by many different people and organizations. However, it is important that you know and understand what a Perl script does before running it on your virtual server.

While most scripts available are written by knowledgeable, experienced programmers, other scripts have the ability to cause havoc on your virtual server. A poorly written Perl script can cause severe problems, regardless of what kind of server (Sun, LINUX, Windows NT) and how much resources are available (RAM, CPU, etc.) on the server! In short, we highly recommend that you do not just install various free Perl scripts on your virtual server.

If you are new at Perl and wish to experiment, we suggest you start out by first installing some of the Perl scripts we make available through your Personal Control Panel. These scripts are safe and will run without any need to configure on your virtual server.

If you are attempting to install a Perl script you did not author yourself, it is very important that you make sure the program does not consume an excessive amount of CPU run-time and/or RAM. We suggest you log into Telnet and view "top" and see how much resources a program consumes. Below is how this would be done:

  1. Log into your virtual server via Telnet. If you do not know how to do this, see our Telnet tutorial.
  2. Change directory (cd) into the directory where the perl script resides.
  3. Now execute the following command in Telnet: perl <scriptname>;top
  4. Now watch the SIZE, STATE, TIME, and CPU columns.

Be sure to replace <scriptname> with the actual name of the Perl script in question. The command in Step #3 will simply execute the Perl script and immediately run top, which displays the resource usage of any processes running under your userid.

The SIZE column will display the amount of memory each process is taking, expressed in either Kilobytes (K) or Megabytes (M). Remember, your server runs with 1,024MB of RAM! The STATE column displays the state of the process. A process can be either sleeping or running on the processor. The TIME column displays to the total amount of time, in seconds or hours, a process has been running on the processor. Finally, the CPU column displays the percentage of the CPU the process is currently using.

As a guideline, a process is generally considered excessive if it has been running on the CPU for more than 10 seconds, and/or is taking up more than 20MB of RAM. Additionally, a process is considered excessive if it takes up more than 50% of the CPU at anytime. Finally, a client is considered to be using an excessive amount of system resources when there are more than 8 processes running at anytime consistently under the same userid.

In summary, we strongly suggest you watch top for a good indication of what kind of system resources a new Perl script requires.

     

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