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by Jayaram V
The Common Gateway Interface (CGI) program is used to provide
interactivity to
web applications so that they become responsive and
dynamic to the requests made by a web browser or a client application. A CGI program contains
a set of conventions that enable the client programs and the web servers
to communicate. The web server usually
acts as an intermediary between the CGI program and the client browser.
When a client browser sends a request to the web server, it executes the
CGI program based on the input received and sends the output back to the
web browser for processing. A commonly known example is a program that
receives a stock ticker symbol as an input and returns relevant
information about the stock including its current price. Another example
is a program that accepts information about a website from a user and
sends it to the webmaster as a feedback. CGI programs can be written in
any programming language and they can also be used to interact with
other programs or CGI programs during their execution.
A CGI program
would not do the following.
- it does not interact with a user directly.
- It does not interact directly with a web browser or a graphical
interface. In other words it does not display or retrieve
information from menus, commands and other interactive features of a
client browser.
- It does not create graphics or windows by itself.
A program must meet the following criteria to be qualified as a CGI
program.
- One should be able to execute it directly by typing its name from
the command line. A java program does not qualify to be a CGI
program because it cannot be executed in the java virtual machine
unless we type "java program-name" in the command prompt.
- The program should generate a valid content-type header.1
Following are some of the advantages and disadvantages of CGI
programs.
Advantages
- CGI programs are portable and work on a wide variety of web
servers and platforms.
- They are language independent. You can write then in any language
and make them work in a wide variety of environments. Some of the
programming languages good enough to write your CGI scripts are Perl,
UNIX Shell, C language, Visual Basic, Python, C# and Java.
- They provide simple interfaces for the clients to interact with
the web servers.
- They are scalable programs and you can use them to perform simple
tasks in the application layer as well as more complex tasks such as
interacting with databases and shopping carts.
- They provide interactivity to a web application and enhance user
experience.
- CGI programs are cost effective. By using them businesses can
lower their development and maintenance costs.
Disadvantages
- The CGI programs are memory intensive programs. Every time a request is made
to a server, it has to launch the CGI program. If they are written in a
scripting language, the
interpreter for the scripting language has to evaluate the entire
script to execute the CGI program each time the program is
initiated. If the server has busy traffic, repeated client side
requests would consume a great deal of server resources and impact server
performance. This problem is minimized to some extent by
CGI scripts written in a compiled or interpreted language like C where there is no need for
an interpreter to read the CGI program code separately.
- CGI programs are not easy to write. They require complex
programming and designing skills on the part of the web developers
since a lot depends upon how they are implemented in the server
environment.
- If proper care is not taken, CGI programs may compromise server
security.
- Most of the CGI programs are well known, free and easily
available. Their strengths and vulnerabilities are known to most web
developers. This often result in their exploitation and misuse.
CGI was developed at National Center for Supercomputing Applications
(NCSA) during the initial phases of development of the first web server
that went by the name NCSA HTTPD. It was added to the server
during the 1.0 release. NCSA was the place where most of founders of
Netscape worked. During the development of the web server, Rob McCool
created an initial specification for an interactive process with in the
web server functionality, before it was recognized as a separate and
independent CGI program.
CGI programs may accept as inputs html code, graphics, word
documents, binary input, text files, audio and video files and so on.
The data is usually submitted through web forms or programmatically
through preexisting objects such as components and other executable
programs. CGI programs may not perform as expected unless they receive
valid input. So validation checks are necessary before the data is
passed on to them.
Because of the limitations in developing and executing CGI programs
and the disadvantages we have discussed above, many CGI alternatives
have been developed and marketed commercially in recent years. Most of
these are proprietary solutions that attempt to tackle the problems
associated with CGI applications. Some of these alternatives like ASP,
Cold Fusion and PHP are HTML based where you embed scripts in the HTML
code and some like mod_perl, NSAPI and ISAPI interface directly with the
web server without a CGI interface.
Following are some of the well known websites where you will find tons
of cgi scripts and examples.
CGI City -CGI City was formed with the purpose of providing a one-stop-shop for people with CGI requirements. We have taken great efforts to put together a very comprehensive set of links that will address most, if not all, of your CGI needs. This site caters to all people from all over the world with no discrimination for CGI proficiency. Our packaged cgi scripts have been sold to customers in 16 different countries. Similarly, our custom programming services have been contracted by customers from various cities all over the world. A novice as well as the seasoned CGI programmer and even the non-programmers will find CGI City a useful site worth
bookmarking.
Perl.Com - Perl.com is the central web site for the Perl community. Launched by Tom Christiansen, perl.com provides a starting place for finding out everything about
Perl. O'Reilly & Associates, Inc., the premier publisher of books about Perl, is the sponsor of perl.com and the goal is to make perl.com an even better resource for programmers, new and advanced
WillMaster.com -CGI is fast becoming essential to many online businesses. WillMaster.com offers a wide variety of powerful programs: Tools for Communication, Site content, Site promotion, Forms processing,
E-zines, E-mailing, Web site administration. You can use WillMaster.com CGI programs to automate your site, facilitate sales, foster trust, and bring your customers back for more.
Matt's Script Archive, Inc: Welcome to Matt's Script Archive. Offering free CGI scripts to the web community since 1995. Get your free Perl CGI scripts for
FormMail, Guestbook, WWWBoard, Simple Search, csPublisher, Article Manager, Counter,
TextCounter, Random Text, TextClock, Free for all Links, Random Link, HTTP Cookie Library, Countdown, Random Image, SSI Random Image,
TextCounter, C++, TextClock, C++.
CPAN - CPAN is the Comprehensive Perl Archive Network, a large collection of Perl software and documentation. You can begin exploring from either
http://www.cpan.org/, http://www.perl.com/CPAN/ or any of the mirrors listed at
http://www.cpan.org/SITES.html and http://mirror.cpan.org/. Note that CPAN is also the name of a Perl module,
CPAN.pm, which is used to download and install Perl software from the CPAN archive. This FAQ covers only a little about the CPAN module and you may find the documentation for it by using perldoc CPAN via the command line or on the web at
http://theoryx5.uwinnipeg.ca/CPAN/perl/CPAN.html.
BigNoseBird: There are over 300 pages of tutorials, reference materials, and other free resources located on this site. The links below list major content areas. The collection includes form processing,
guestbook, banner rotation, site search and more. You can also browse through several useful tutorials and articles.
CGI World -
CGI-World.Com is a Department of i2-Services Incorporated. Operations began in 1996 offering interactive, web based internet polling software. Our goal since 1996 has been a dedication to Developing, Marketing, and Supporting high quality, full featured web based applications. Years later
CGI-World.Com and our Partners have developed a wide variety of web based products that provide solutions to everyday web tasks.
Cliff's Perl Scripts - Welcome to my perl script collection! This page is designed for webmasters who are looking for free CGI scripts. If you don't fall into that category, I suggest you check out my unique brand of immature low-brow humor at Shaven Ferret Productions.
Free CGI/Perl Scripts - Easy to Use: Dozens of free and professional CGI / Perl scripts. Download our free CGI scripts, get to know our superior quality, then come back and check out the rest of our products. If you do not see the script you are looking for, we can custom build it for you. When you buy a script, it can be used on one domain only. If you want to extend the license, go here. If you want to see what we have in the works, look here.
Four-Runner.com: Welcome to
Four-Runner.com - The IT Developers No.1 choice for resources of every description Developers available to design, program and/or your Internet and/or Intranet site and/or application: Online Enquiry Form.
LockedArea.com - LockedArea.com is the centre point for distribution of the internationally acclaimed Locked Area program. Locked Area is a very powerful Perl script designed for creating password protected member communities for web sites. It offers all the great features that you'd expect of a program of this type as well as some others like members area statistics, powerful administration panel and an easy to use, 60-second installation program.
PerlMonks.org : Welcome to the Perl Monastery. We hope your stay is long and enjoyable. You are probably wondering what Perl Monks is all about. Hopefully this page will answer some of those questions. What Perl Monks is: Our attempt to make learning Perl as nonintimidating and easy to use as possible A place for you and others to polish, improve, and showcase your Perl skills A community which allows everyone to grow and learn from each other.
Perl Circus: This site is about
Perl. Its not actually about circuses but I definitely think a good Perl coder is a lot like a circus performer -- somewhere between a contortionist and a trainer of wild beasts. And I mean that in a good way!
CGIScriptReview.com: CGIScriptReview.com is basically aimed to be your one-stop resource for reviews of all the most popular CGI scripts available on the internet. We have reviews of all the most popular scripts available. To get started, please select a category to look in from the listing below to find and read a review. All reviews are written by people who are not associated with the script development so as to make sure they are honest and true to life. We currently have 10 CGI script related reviews listed.
Perl Coders: PerlCoders is a company started on the premise that webmasters should not have to pay an arm and leg for top quality programming. While most CGI programmers were charging a lot of money to make each script, we decided to start creating ready made solutions to common needs at membership pricing. What had started with one script has now become the largest single source for pre-made programs on the net.
ScriptSearch: ScriptSearch.com said to be the largest and most well-known programming directories anywhere. ScriptSearch's comprehensive programming directory is more intuitively organized by programming language with subfolders with various script categories. Rating features allow you to find the most popular and most useful resources according to the rest of our visitors. Its even a breeze to bookmark your favorite listings on your own "My Favorites" page, that you can easily return to. And there lots more inside.
Solution Scripts: The Script Vault holds all our professional turnkey perl programs. These programs are top quality, easy to set up and easy to run. We have created these programs to be greatly customizable so they can match the look of any site. Simply click on the program name for more information on each. Should you have any questions, you can contact us via our contact form, or post a message in our help forums We also have several free to use scripts, they can be found in our Warehouse.
Perl Foundation: The Perl Foundation is dedicated to the advancement of the Perl programming language through open discussion, collaboration, design, and code. The Perl Foundation coordinates the efforts of numerous grass-roots
Perl-based groups including: International Yet Another Perl Conferences, Holds the copyright on Perl 6 and Parrot,
perl.org, Perl Mongers, PerlMonks.
Perl Clinic: The Perl Clinic is a commercial Perl support service operated by ActiveState Corp. ActiveState has many years of in-depth experience with Perl applications and Perl internals on a wide range of platforms. Perl Clinic support is available on a per-incident basis, as a prepaid support contract, or through ActiveState's
PerlDirect. For pricing information, see Pricing.
CGIExpo.com: 5309 verified CGI,
PHP, and JavaScript resources listed ...and growing.
The CGI Resource Index: 4369 CGI resources listed in 339 categories at The CGI Resource Index.
CodeHound Perl - Unlike other Internet search engines, CodeHound is specifically designed for programmers. Instead of using a larger search engine like Google or AltaVista, a CodeHound user comes to
CodeHound, selects a programming language, and lets CodeHound search the best Web sites and newsgroups dedicated to that language. For example, a search on our SQL search engine is categorized by
RDMS: SQL Server, Oracle, IBM DB2, Informix, Sybase, Microsoft Access, MySQL, and others. No other search engine on the Internet offers such power!
dev.perl.org - Perl 6 - The official
site for the development of Perl 6, the next generation of the Perl programming language.
Kamango.com: PERL Channel - Wide range of Perl scripts, programs and tutorials.
O'Reilly Network: Perl Weblog - Features links and commentary by a variety of authors.
O'Reilly Perl Center - Current and past products, resources, and news on O'Reilly and Associate's Perl involvement.
Perl Cabal - Humorous profiles of Perl luminaries.
The Perl Institute - Non-profit organization dedicated to making the incredibly useful Perl language even more useful for everyone. Supports Perl creators, developers, maintainers, and users. Recently disbanded, and is being incorporated into the Perl Mongers.
PerlParaphernalia - By Mark-Jason
Dominus. Perl Advanced Techniques Handbook (drafts). Hints, articles, Perl modules, programs.
Perl Quiz - Test your knowledge of Perl by answering 15 questions at basic, intermediate or advanced level. Questions change every time.
The University of Florida Perl Archive - Archives of
comp.lang.perl; documentation; scripts; and source code for perl.
use Perl - General discussion of perl and issues relating to it, Perl news.
More
Resources On cgi Scripts
Footnotes
1. A Content-Type header
specifies the nature of the data in the body of an entity, by giving
type and subtype identifiers, and also auxiliary information that may be
required in some cases.
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