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CGI ?


davej
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CGI isn't really a language, but a protocol for applications. PHP is a CGI application. Or to be more precise, it can be used as a CGI application.Most other languages that have a CGI reputation (Ruby, Perl) aren't exactly CGI applications themselves... but they do allow you to output CGI compatible output.In fact, if you run a PHP from "php.exe", and output HTTP headers using "echo", you are in essence creating a CGI application.

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Ok, I had scanned the Wikipedia entry before posting my question and my understanding was that CGI implies that the webserver is set up to launch some executable program in response to particular page accesses -- but why do this? Why not just use ordinary server-side code? Are there some things that the CGI approach is better at? Or is CGI an older, semi-obsolete approach? Thanks

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Yes. That's what CGI is - a protocol that defines what an executable program should expect as input (in STDIN, environment variables, etc.), and what it is expected to write in STDOUT for the web server to handle it properly.Server side code boils down to one of 3 approaches:1. A self-contained web server. No Apache or something like it needed - you just create a program using a certain language/framework, compile it (no way around that...), and start the generated executable.2. A web server module. This is one of the ways in which PHP could run as, and one way in which you could write your own modules. The server may provide a way for you to write interpreted rather than compiled code (which is what the PHP Apache module does).3. A CGI/FastCGI executable. This is the other way PHP runs as. FastCGI is basically the same as CGI, except that the executable is expected to remain available after the first request. And PHP just happens to be a (Fast)CGI application that lets you execute interpreted code.I guess what I'm trying to say is that "ordinary server-side code" is a very loosely defined term... basically, there's no such thing.It's like you're asking "Why should I use XML if I can just use XHTML or RSS?".

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Ok, I'm under the impression that almost all webservers use Apache or Microsoft IIS server software. The server software then interprets HTML files or somehow launches server-side code which might be Java/JSP, ASP, ASP.NET, PHP, or I don't know what else. Is CGI exactly the same thing or is it something different? Thanks

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or somehow launches server-side code which might be Java/JSP, ASP, ASP.NET, PHP, or I don't know what else.
BINGO! That's what CGI is. It's the "somehow" in the sentence above - the most popular way in fact, although from the above list, only PHP uses it.
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People who use Perl or Python do so because they feel that it is better suited or faster for what they're trying to do. In the absence of benchmarks where you specifically test each language, it pretty much comes down to personal preference. People use Perl because they are Perl programmers.

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