Common what?
CGI, or "Common Gateway Interface", is a standard which lets Web browsers run programs on your server. CGI is NOT a programming language on its own. Essentially, it is the term used to refer to any program that can run from a web server. CGI is actually the interface, not the program itself. A CGI program or script can be written in any of a multitude languages. C++, Perl, Java, or even a windows executable can be CGI, as can many others.
Perl is probably the easiest of the commonly used languages for CGI - not that it is very easy, but it can be understood well enough to make modifications if you need to. I've never learned to do more than patch already written scripts, but I did have to learn how to use the interface, in order to make them run on my server. This means mostly that you need to understand paths, and how your server finds things - you will usually find all this information in your servers help files, but you will still need a basic understanding. By the way, a program is compiled, a script is not, that is the basic difference - a script needs a compiler to run. So, if your web host has a Perl compiler and a C++ compiler (the ones I've found most often), you can run scripts in those languages, and you can also run any program compiled to run on your server's operating system.
The best tip I can give you is that there are a lot of people out there who are good programmers and scripters, have written highly useful scripts and programs, and are giving them away! Get one someone else did and modify it, unless you really cannot find anything for what you need. Most of them will give out source code for compiled programs, various restrictions apply. Please note - CGI can be any of a number of programming languages - Perl is the most common, followed by C++ and Java servlets(not Java script, which is totally different, running on the client's machine.)
- Web Teacher
- They sell interactive tutorial software, but their CGI tutorial is online, I suppose as an example. They also have a Java tutorial. Both basic, but helpful for the beginner.
- Common Gateway Interface
- A guide from the people who brought you Mosaic. Well -written and one of the first I ever accessed.
- CGI, Perl, Freeware
- Also the repository of the definitive FAQs for WWW and CGI (by Thomas Boutell). A must read for those just starting.
- CGI Extremes - A Perl and CGI Script Resource
- The site is bit ad intensive- but has some very good free scripts.
- Extropia Open Source
- Free CGI Scripts. This was Selena Sol's script archive - you can now buy a license for support and upgrade notifications, but the scripts are still free. You can also buy her book, which is excellent.
- Scripts Archive
- Matt's Perl CGI Scripts -Like Selena he's been around a while. Good scripts.
- Scott Crevier
- This archive contains some CGI scripts, some UNIX shell utilities and a few toys for Webmasters.
- Script Search
- Search for all kinds of scripts in all languages (programming languages that is). Has a huge database of scripts. If you need a particular script, you'll probably find it here. Some for pay, most free.
- CGI Resource Index
- Mega index to CGI resources (why am I bothering? they've got most of it).