Every time I see Ruby or Python discussed in the context of web development, it's always with a framework (Rails for Ruby, Django for Python). Are these frameworks necessary? If not, is there a reason why these languages are often used within a framework, while Perl and PHP are not?
I can only speak towards Ruby - but, no, you don't need a framework to run Ruby based pages on the web. You do need a ruby enabled server, such as Apache running eruby/erb. But, once you do, you can create .rhtml files just like RoR, where it processes the inline ruby code.
The short answer is no, they are not necessary. In ruby you have .erb templates that can be used in a similar way as you use PHP pages. You can write a site in ruby or Python using several technologies (Rails-like frameworks, Templates or even talking directly with the HTTP library and building the page CGI-style).
Web frameworks like Python's Django or Ruby's Rails (there are many) just raise the level of abstraction from the PHP's or ASP's, and automate several process (like login, database interaction, REST API's) which is always a good thing.
"Need" is a strong word. You can certainly write Python without one, but I wouldn't want to.
Python wasn't designed (like PHP was, for example) as a direct web scripting language, so common web-ish things like connecting to databases isn't native, and frameworks are handy.
EDIT: mod_python exists for Apache, so if you're merely looking to write some scripts, then Python doesn't need a framework. If you want to build an entire site, I'd recommend using one.
From a Pythonic point of view, you'd absolutely want to use one of the frameworks. Yes, it might be possible to write a web app without them, but it's not going to be pretty. Here's a few things you'll (probably) end up writing from scratch:
Templating: unless you're writing a really really quick hack, you don't want to be generating all of your HTML within your Python code -- this is a really poor design that becomes a maintainability nightmare.
URL Processing: splitting a URL and identifying which code to run isn't a trivial task. Django (for example) provides a fantastic mechanism to map from a set of regular expressions to a set of view functions.
Authentication: rolling your own login/logout/session management code is a pain, especially when there's already pre-written (and tested) code available
Error handling: frameworks already have a good mechanism in place to a) help you debug your app, and b) help redirect to proper 404 and 500 pages.
To add to this, all of the framework libraries are all heavily tested (and fire tested). Additionally, there are communities of people who are developing using the same code base, so if you have any questions, you can probably find help.
In summary, you don't have to, but unless your project is "a new web framework", you're probably better off using one of the existing ones instead.
Framework? Heck, you don't even need a web server if you're using Python, you can make one in around three lines of code.
As to the why:
The most plausible thing I can think of is that Perl and PHP were developed before the notion of using frameworks for web apps became popular. Hence, the "old" way of doing things has stuck around in those cultures. Ruby and Python became popular after frameworks became popular, hence they developed together. If your language has a good framework (or more than one) that's well supported by the community, there's not much reason to try to write a Web App without one.
A framework isn't necessary per se, but it can certainly speed development and help you write "better" code. In PHP, there are definitely frameworks that get used like CakePHP, and in Perl there are many as well like Mason and Catalyst.
The frameworks aren't necessary. However, a lot of developers think frameworks ease development by automating a lot of things. For example, Django will create a production-ready backend for you based on your database structure. It also has lets you incorporate various plugins if you choose. I don't know too much about Rails or Perl frameworks, but PHP frameworks such as Zend, Symfony, Code Igniter, CakePHP, etc are used widely.
Where I work at we rolled our own PHP framework.
Are these frameworks necessary?
No. They, like any 'framework', are simply for speeding up development time and making the programmer's job easier.
If not, is there a reason why these languages are often used within a framework, while Perl and PHP are not?
PHP and Perl were popular languages for building web sites well before the idea of using frameworks was. Frameworks like Rails are what gave Ruby it's following. I'm not sure that Python or Ruby were that common as web languages before they were backed by frameworks.
These days, even PHP/Perl web developement should be backed by a framework (of which there are now many).
By no means are those development frameworks required. But as with most development environments, your productivity will increase exponentially if you have a supported framework to reference and build your applications on. It also decreases the training needed to bring others up to speed on your applications if they already have a core understanding of the framework that you use.
For python, the answer is No you don't have to. You can write python directly behind your web server very easily, take a look at mod_python for how to do it.
A lot of people like frameworks because they supply a lot of the boilerplate code in a reliable form so you don't have to write it yourself. But, like any code project, you should choose the tools and frameworks on their merit for your problem.
You can certainly write CGI scripts in either language and do things "raw".
The frameworks (ideally) save the trouble of writing a pile of code for things that other people have already handled (session handling, etc.).
The decision probably comes down to what you need to do. If the framework has the features you need, why not use it. If the framework is going to require extensive modifications, it might be easier to roll your own stuff. Or check out a different framework.
The python library has numerous modules for doing cgi, parsing html, cookies, WSGI, etc:
http://docs.python.org/library/index.html
PHP has a lot of frameworks. Probably more then most. In Ruby most use Rails so thats what you hear, and Django for Python is mentioned more then not.
But with PHP you have many to choose from.
List of web application frameworks
Any language that can "print" can be used to generate web pages, but frameworks handle a lot of the HTML generation for you. They let you concentrate more on the content and less on the details of coding the raw HTML.
Related
I have been developing a plain JSP/Servlet web application, which focuses mainly in collecting large sets of data through JSPs, processing them and finally commiting them to a MySQL database. Imagine something like a declaration of assets for a pretty big number of people.
While it works pretty good now, the code is really jumbled up and since I now have the time, I am thinking of completely redesigning the whole application in a more sophisticated and reusable way. My main problem is that forms are built mainly through jQuery (my form_build.js and form_validate.js files span over 600 lines each at the moment), and the back-end java code is jumbled up since there is massive use of name[counter] input fields.
I.e. The user can add 5 assets in the form, where he has to submit something like 30 fields of information on each one. The form sends them in the form of attribute[asset_counter].
If I managed to make myself clear, I have been looking into the Google web toolkit - which I had no idea of before - and from what I gather mastering it will take some time for me. Is it worth the trouble, or is it aimed at something completely different? And is there a framework or technique that can handle efficiently what I need?
Frankly, I am a senior java developer and I used a lot of jsp/jsf web applications accompanied by EJB, webservice, simple spring web apps, and I recently came up to use GWT.
It's a very nice platform, it has the following advantages:
All the code is compiled to html/JS which is better in terms speed
and browser understanding agilty
It uses built in JSON xml transer (nice approach)
It use built in AJAX (nice approach)
It use it's own cleint server platform (no need to use other
libraries for each one)
It will adopt to any browser (strong competetor)
drowbacks:
Sometimes it takes time to load in the browser (specially when using
FlexTables)
I advise you to use it!
GWT is a very powerful toolkit, and from what I understand it might help you to better organize you client side code. But you also have to consider some high-level JS framework like backbone.js+require.js or Google Closure. Time spent to learn this frameworks this bascially the same as for GWT, the choice basically depends on what your team prefer, JS or Java. In most cases when logic on client side gets very complicated, I will choose GWT.
I usually write web apps in PHP, Ruby or Perl. I am starting the study of Scheme and I want to try some web project with this language. But I can't find what is the best environment for this.
I am looking for the following features:
A simple way of get the request parameters (something like: get-get #key, get-post #key, get-cookie #key).
Mysql access.
HTML Form generators, processing, validators, etc.
Helpers for filter user input data (something like htmlentities, escape variables for put in queries, etc).
FLOSS.
And GNU/Linux friendly.
So, thanks in advance to all replies.
Racket has everything that you need. See the Racket web server tutorial and then the documentation. The web server has been around for a while, and it has a lot of features. Probably the only thing that is not included is a mysql interface, but that exists as a package on PLaneT (Racket package distribution tool).
UPDATE: Racket now comes with DB support, works with several DBs including mysql.
You may want to have a look at Clojure:
Clojure is a dynamic programming language that targets the Java Virtual Machine. [...] Clojure provides easy access to the Java frameworks, with optional type hints and type inference, to ensure that calls to Java can avoid reflection.
Clojure is a dialect of Lisp, and shares with Lisp the code-as-data philosophy and a powerful macro system.
Interop with Java is straightforward in Clojure, so you can re-use any existing Java libraries as you need. I'm sure there are plenty that are useful for web development.
clojure-contrib has an SQL API, and there is ClojureQL as well, which should cover your DB access needs.
There is a web framework for Clojure called Compojure under development. There may be others, too.
Clojure's source is available on github under the EPL. Getting it running on Linux is easy; I just clone the git repos and run ant.
You can do web development with guile scheme. Its standard library includes the (sxml simple) module that is very useful for html generation, manipulation, and parsing. The guile-www library adds support for http, cgi, etc. The guile-dbi library provides access to MySQL and other databases. With these building blocks, you can implement everything from simple cgi scripts to web applications with their own HTTP server.
Try Weblocks, a Common Lisp web framework:
http://weblocks.viridian-project.de/
I've written a pretty extensive tutorial/ebook on the topic: http://lispwebtales.ppenev.com/
Quick summary:
It uses Common Lisp
It uses the Restas framework
It has examples for pretty much most of basic web development, including DB access, authentication, HTML generation and templating.
Since the Restas documentation is pretty much out of date, my tutorial is the closest thing to up to date docs.
Shows a few of the more advanced features, like policies, which allow you to write pluggable interfaces, for instance you can write a data store layer, and write back-ends for different storage mechanisms with relative ease, the module system which allows you to write reusable components, like auth frameworks and things like that.
It covers things like installing lisp, setting up the ASDF build system and the quicklisp package manager etc.
It's free online, and as soon as I finish it it will be free on leanpub as well. The source is on https://github.com/pvlpenev/lispwebtales under a CC license, the source code is MIT. Not all of it is published yet, and I'm in the process of revising.
This may be what you are looking for.
http://www.plt-scheme.org/
http://docs.plt-scheme.org/web-server/index.html
http://common-lisp.net/project/cl-weblocks/
If you are interested in Common Lisp to be exact and do not want to go the weblocks route I would recommend the following setup:
Use SBCL on Linux but with multiple thread support
Use Hunchentoot as a web server which will provide you with all the server processing required including sessions and cookies
Use ClSql to communicate with MySql it has ample documentation and is very stable.
For the HTMl generation you can use Dr Edi Weitz Cl-WHO (very well documented).
Note all the above are under GPL or similar license (one that works more for lisp programs)
Gambit Scheme has its own solution to web apps as well. It uses the Spork framework, based o the Black Hole module system (both by Per Eckerdal).
Andrew Whaley has an initial tutorial on how to get Gambit, Black Hole and Spork running a web app under Apache using mod_proxy. You might want to take a look at that.
On a (possibly) related note, Gambit will also compile your stuff to C and then to an executable, if you feel so inclined.
Paul Graham (and friends) made a lisp dialect specifically for writing basic web applications. It's called Arc, and you can get it at arclanguage.org.
It's probably not suited for really big complex websites and I'm not sure what state it's database support is at but Paul Graham knows how to write web applications in lisp, so Arc will make the HTTP/HTML part easy for you while you spend most of your brain cycles learning the lisp way.
Weblocks is nice tool for building web apps in Common Lisp, but a bit too heavy-weight for me.
We use the following stack:
OpenMCL (open source Lisp, very nice)
Portable Allegroserve (web server, HTML generator)
Our own Rails-like tools for doing Ajaxy stuff (update: this has now been open sourced as WuWei)
A variety of CL libraries like cl-json, cl-smtp, md5
I use my own, customized version of Scheme, derived from MzScheme. It has a new, simple web-application framework, a built-in web-server (not the one that comes with MzScheme) and ODBC libraries. (http://spark-scheme.wikispot.org/Web_applications). The documentation may not be exhaustive, as this is more of a personal tool. But there are lots of sample code in the code repository.
Clojure is a Lisp dialect which may interest you. At this point there's a pretty decent web development stack. I can recommend a few things:
The leiningen dependency manager which makes is really easy to install and manage libraries that you're using. Pretty nice set of plugins for it too. There's even a plugin for Clojurescript, which is a language based on Clojure that compiles to Javascript.
The ring HTTP server abstraction. Its used in most actual web frameworks. Its a pretty good idea to learn that first before jumping into an actual framework.
hiccup is a HTML dsl/templating language written in Clojure. Its very expressive! Reminds me a bit of Jade, in a sense.
composure would have to be the most popular web framework for Clojure. Its essentially a routing library like express.js.
Let's see what can be done with Common Lisp.
The state of the Common Lisp ecosystem (2015) and the Awesome Common Lisp list show us a couple of modern frameworks (Caveman, Lucerne, all built on the new Clack web application server, an interface for Hunchentoot and other servers). Let's discuss with our own findings.
update 2019: there's a new tutorial on the Common Lisp Cookbook: https://lispcookbook.github.io/cl-cookbook/web.html It covers routing, template engines, building self-contained binaries, deployment, etc.
update: a bit later, I found out Snooze, by the creator of Sly or Emacs' Yasnippet, and had a much better impression than say Caveman. Declaring endpoints is just like declaring functions, so some things that were tedious in Caveman are obvious in Snooze, like accessing the url parameters. I don't have much experience with it but I recommend checking it out.
update june 2018: also don't miss the ongoing rewrite of Weblocks, it's going to be huge ! :D http://40ants.com/weblocks/quickstart.html Weblocks allows to build dynamic webapps, without a line of Javascript, without separating the back and front. It is components-based, like React but server-side. It's very alpha as of writing (june 2018), but in progress, and it's working, I have a couple simple web apps working.
A simple way of get the request parameters (something like: get-get #key, get-post #key, get-cookie #key).
I found easier the Lucerne way, it iss as simple as a with-params macro (real world example):
#route app (:post "/tweet")
(defview tweet ()
(if (lucerne-auth:logged-in-p)
(let ((user (current-user)))
(with-params (tweet)
(utweet.models:tweet user tweet))
(redirect "/"))
(render-template (+index+)
:error "You are not logged in.")))
Caveman's way has been less clear to me.
Mysql access
Caveman advertises database integration (with Fukamachi's Datafly and sxql).
You can just use clsql or the Mito ORM: https://lispcookbook.github.io/cl-cookbook/databases.html
HTML Form generators, processing, validators, etc.
I don't know if there are form generators out there. edit: there are: cl-forms and formlets, or again 1forms, working with Caveman2.
Caveman does not have one (issue raised in 2011).
Helpers for filter user input data (something like htmlentities, escape variables for put in queries, etc).
Ratify is an input validation library, not integrated into a framework though.
FLOSS and GNU/Linux friendly: ✓
Other web stuff
Speaking about web, there are other nice libraries in CL land:
web servers: Woo is a fast HTTP server, faster than Nodejs (beware of charts…), wookie is an async http server,
Dexador is an HTTP client
Plump, lquery and CLSS make it easy to parse html and query the DOM.
cl-bootstrap offers twitter-bootstrap shortcuts for the cl-who templating engine (which kind of replaces Jade/Pug, even though we have usual templates too).
Ajax in Lisp
(remember, with Weblocks, see above, we might not need those)
With ParenScript, we can write JavaScript in Common Lisp, without living our usual workflow, and we can thus use the fetch web API to write Ajax calls.
Clojure would be perfect for this. With some very short, clean code, you can implement some very complex applications, such as blogs or forums.
You might want to consider the awful web framework for Chicken Scheme.
Natively supports PostgreSQL and SQLite
Built-in easy support for sessions
Shortcuts for some webdev idioms, like the (ajax) procedure
Your app can be easily compiled to a static executable (via csc -static) for easier deployment
The collection of all chicken libraries (eggs) isn't as versatile as in some other programming languages, but isn't awful either
So, there are several languages which will allow you to create a website, as long as you configure the server(s) well enough.
To my knowledge, there is:
PHP
ASP.NET
Ruby(on rails, what is
that all about?)
And thusly, my knowledge is limited. Ruby and ASP, I've only heard of, never worked with. If there are other languages, I suppose they have some way to make files containing the needed html. It would then suffice to add a line to the Apache config to associate the file-extension.
And if other languages: are there any notable characteristics about the one(s) you mention?
ANY language can be use to make a dynamic website - you could do it in COBOL or FORTRAN if you were twisted enough. Back in the olden days (about 10 years ago) most dynamic websites were done with CGI scripts - all you needed was a program that could read data from standard input and write data (usually HTML) to standard output.
Most modern languages have libraries and frameworks to make it easier. As well as the languages you have already mentioned, Java, C# and Python are probably the most common in use today.
Typically a web framework will have:
a way of mapping URLs to a class or function to handle the request
a mechanism for extracting data from a request and converting it into an easy to use form
a template system to easily create HTML by filling in the blanks
an easy way to access a database, such as an ORM
mechanisms to handle caching, redirections, errors etc
You can find a comparison of popular web frameworks on wikipedia.
How can you forget Java ? :)
Python
It runs on Windows, Linux/Unix, Mac OS X, and has been ported to the Java and .NET virtual machines.
Python is a perfect scripting language for web applications, e.g. via mod_python for the Apache web server. With Web Server Gateway Interface a standard API has been developed to facilitate these applications. Web application frameworks or application servers like Django, Pylons, TurboGears, web2py and Zope support developers in the design and maintenance of complex applications. Around libraries like NumPy, Scipy and Matplotlib, Python is a standard in scientific computing.
Among the users of Python are YouTube and the original BitTorrent client. Large organizations that make use of Python include Google, Yahoo!, CERN, NASA,and ITA.
This could be for your interest.
Virtually thru CGI all programming languages that produce output may use for web page generation.
Basically, you can use any language (if you are hosting your own server)
Very closely related and very interesting is this article where LISP has been used to build a very succesfull website.
Python has a 3rd party module CherryPy which can be used with or without a http server.
Amongst others: Erlang (YAWS, Mochiweb), Python
JSP has the advantage that it automatically wraps your code in a servlet, compiles that to bytecodes, then uses the just-in-time Java compiler to recompile critical sections into native object code. Not aware of any alternative which allows optimizes your work automatically in this way.
Also allows you to develop and deploy on any combination of Windows, Mac OS X, or Linux.
If you'd like to choose one for the beginning, you should check out PHP first. It gives you the basic clues about how dynamic sites work in general.
After you've become familiar with the basics, I recommend ASP.NET.
Fist off, you should know that ASP.NET is a technology and not a language. (It actually supports any language that can be used on the .NET platform.) Also it is not to be confused with classic ASP. (The old ASP was much more like PHP.)
ASP.NET is very easy to begin with, and after you have some clues about its concepts, you can always dig deeper and customize everything in it. The http://asp.net site is a very good starting point, if you are to learn it. I think it is really worth the effort, because even if you choose not to stick to it, it will give you some interesting ideas and concepts.
I tell you its most important advantages:
The code is compiled (and NOT interpreted like PHP), and it has a very good performance. (In a performace comparsion, it is 10-15 times faster. http://www.misfitgeek.com/pages/Perf_Stat_0809.htm)
It can be run on Windows without effort, and on Linux / Mac / etc using the Mono project.
It implements the Separation of Concerns principle very well.
It has most of the general functionality you'll need built-in. (Such as membership, roles, database management, and so on.)
If you were going to start building web sites as a consulting business on the side -- keeping your day job -- and you also had a toddler and a wife, what frameworks/tools would you pick to save you typing?
Any language.
I'm looking for a productivity superstar stack that won't tie my hands too much when I have to update the site 6 months later, or "evolve" the data model once in production.
It needs to allow me to say "yes" to the client: community features, CMS, security, moderation, AJAX, ...
I would suggest Django. Super simple to get something up and running really quick. You are using Python which has a large library to go with it. For me Ruby on Rails would be a close second.
I'd probably look at DotNetNuke. Its easy to set up (a lot of hosts will do it for you) and easy to use and put together a custom site that business's will be able to maintain in the future.
Its fairly easy to create custom modules that are specific to a business and hundreds of modules for sale (or free) that can be integrated into DNN for special uses.
Take a look at Microsoft's Sharepoint server if you'd like a pre-made framework with many options for plugging in your own code. Sharepoint is kind of a world unto itself but it is a very powerful environment.
Update: I'm surprised to have been voted down on this one. Keep in mind that the questioner specifically requested frameworks that included a CMS. Sharepoint meets this criteria - unlike straight .NET or other web development frameworks.
If you are going to vote the entry down, I think you owe it to the person who asked the question to explain why you don't think he should not even explore it as an option. You could be right - collective wisdom is what voting on SO is all about. But without an explanation, we don't know why you think you are right.
My answers are going to revolve around the .NET stack.
Use Master pages and CSS templates. This makes it so much easier to pop in a new look and feel for your customer.
For sure I'd include the Dynamic Data framework in the .NET world.
Hosting might become an issue for your customer. Questions around managing email addresses, procedures on how to quickly update the website to include the new contact phone number (different for each customer, I'd assume) Consider getting a reseller account on your favorite webhost, and dole out webhosting accounts as appropriate. There are lots of issues around this point. It may turn out to be a nice source of recurring revenue.
Build yourself a few patterns including a database wrapper which would handle all your data calls (i.e. a dll which wraps all your data calls, sets up your ADO.NET objects, runs your sproc calls, and picks up the connstring from app.config or something similar.)
This goes a long way to maintainability as well.
I would recomend going with anything MVC in a language you can undertand! Theres a couple of CMS's in python, php and ruby using that design and well... that allows you to be ready for combat for Ajax and expanding anything very fast.
This is definitely not a question that can be answered.
I prefer asp.net webforms because I think it allows for extremely rapid web app development, but I am sure you will receive recommendations for:
asp.net mvc
Ruby on Rails
PHP and some framework
Python and some framework such as Django
I believe PHP has the most pre-built apps that you can use, though asp.net also has the things you are looking for.
All of these platforms and frameworks can do what you want.
Choose between Rails and Django. They both have different strengths. I like Rails better in general, but Django's admin interface can save you a lot of time when you need it.
There's another factor to take into consideration here: what are you the most familiar with? I believe that some studies have found upwards of a 30% loss of productivity when trying to learn a new language/framework.
Sometimes, there's nothing wrong with just sticking to what you know. But if you're interested in what languages/frameworks to learn, I'll refer you to the other posts because the above was the only thing I really have to add.
I recommend looking into Grails. It uses Groovy which is similiar to Java (so if you know this already you're good to go). Groovy runs on the JVM so you can still use all the great libraries already available for Java. Yet, since it's a dynamic language with a lot of the similar bells and whistles like Ruby you can use closures and that kind of neat stuff when you need/want to. And you're not slowed down by Java's traditonal slow compile-deploy-test development cycle.
Grails is already setup with Hibernate and Spring. You can create CRUD application in practically no-time (pretty much like Rails applications), and at the same time drill down and be able to control every little details since it's built on such proven and well-supported technologies. In addition there's literally hundreds of plugins available that helps you easily set up things like mailing lists, security, AJAX components and so on.
Otherwise, if you want to set up a community site and don't want to code a single line you could always check out ning.com.
A few years ago I did a lot of work with CGI.pm. I'm evaluating using it again for a quick project. Can someone bring me up to speed on the current state of developing with CGI.pm in the "Web 2.0" world? What are the best libraries on CPAN to use with it? Are there clean ways to include jQuery, YUI, other CSS libs, etc, and do some AJAX. There are of course lots of libraries on CPAN but what works and what is commonly used?
We aren't still doing this?
$JSCRIPT<<EOF;
...
EOF
I realize people are going to offer Catalyst as an answer. However, many people may have legacy CGI.pm apps they simply want to enhance. Is starting over really the best answer?
Personally, I'm no fan of Catalyst (too heavy for my taste) or Mason (mixing code and HTML is bad ju-ju), but I do quite well using CGI.pm for input[1], HTML::Template for output, and CGI::Ajax to provide AJAX functionality where called for.
If you're looking at frameworks, you may also want to consider CGI::Application, which is a widely-used and lighter-weight alternative to Catalyst/Mason.
[1] I can't recall the last time I called anything other than $q->param or $q->cookie from CGI.pm. There are still a lot of tutorials out there saying to use its HTML-generation functions, but that's still mixing code and HTML in a way that's just as bad as using here docs, if not worse.
Consider using something more modern, for example Catalyst. It will make your life much easier and you won't have to reinvent the wheel. I understand that it is just a small project, but from my experience many small projects in time become large ones :)
The "web 2.0" apps that I've worked with usually use client-side JavaScript to request JSON data from the server, then use that data to update the page in-place via DOM.
The JSON module is useful for returning structured data to a browser.
As far as including JavaScript, HTML, or whatever in a here doc - that was never a good idea, and still isn't. Instead, use one of the plethora of template modules to be found on CPAN. For a CGI, I'd avoid "heavy" modules like Mason or Template Toolkit, and use a lighter module for quicker startup, such as Text::Template, or Template::Simple.
Yes, you can write perfect web2.0 web applications WITHOUT using any framework on the server side in any language Perl, Python, Java, etc and WITHOUT using any JavaScript libraries/framework on the client side. The definition of web 2.0 is kind of a loose definition, and I'm guessing by web2.0, you mean Ajax or partial page refresh, then all you would really need is to focus on the following:
Know about the XmlHttpRequest object.
Know how to return JSON object from the server to the client.
Know how to safely evaluate/parse the JSON object using JavaScript and know to manipulate the DOM. Also, at least know about innerHTML. InnerHTML is helpful occasioanally.
Know CSS.
Having said that, it's a lot easier to use some framework on the server side, but not because it's required by web2.0 and it's a lot easier to use some JavaScript on the client like jQuery, mootools, YUI. And you can mix-and-match depends on your needs and your tastes. Most JavaScript provides wrapper around the XmlHttpRequest so that it works across all browsers. No one write "naked" XmlHttpRequest anymore, unless you want to show some samples.
It's perfectly possible to write "Web 2.0" apps using CGI.pm, but you'll have to do the work yourself. From what I've seen, the focus in the Perl development community has been on developing successor frameworks to CGI, not on writing helper modules to let legacy apps get bootstrapped into modern paradigms. So you're somewhat on your own.
As to whether to start over, what are you really trying to accomplish? Everyone's definition of "Web 2.0" is somewhat different.
If you're trying to introduce a few modern features (like AJAX) to a legacy app, then there's no reason you need to start over.
On the other hand if you're trying to write something that truly looks, feels, and works like a modern web app (for example, moving away from the page-load is app-state model), you should probably consider starting from the ground up. Trying to make that much of a transformation happen after the fact is going to be more trouble than it's worth for anything but the most trivial of apps.
I agree with Adam's answer, you probably want to use Catalyst. That being said, if you really don't want to, there's nothing preventing you from using only CGI.pm. The thing is, Catalyst is a collection of packages that do the things you want to make Web 2.0 easy. It combines the various templating engines such as Template Toolkit or Mason with the various ORM interfaces like DBIx::Class and Class::DBI.
Certainly you don't have to use these things to write Web 2.0 apps, it's just a good idea. Part of your question is wondering if javascript and CSS frameworks like jQuery, or prototype require anything from the server-side code. They don't, you can use them with any kind of server-side code you want.
For new apps, if you don't find Catalyst to your taste, Dancer is another lightweight framework you may like. There are also plenty of others, including CGI::Simple, Mojo/Mojolicious, Squatting...
Any of these lightweight frameworks can take care of the boring parts of web programming for you, and let you get on with writing the fun parts the way you want to.
If the jump from CGI.pm to Catalyst seems too daunting then perhaps something like Squatting might be more appropriate?
Squatting is a web microframework and I have found it ideal for quick prototyping and for replacing/upgrading my old CGI scripts.
I have recently built a small "web 2.0" app with Squatting using jQuery with no issues at all. Inside the CPAN distribution there is an example directory which contains some programs using jQuery and AJAX including a very interesting [COMET](http://en.wikipedia.org/wiki/Comet_(programming)) example which makes use of Continuity (which Squatting "squats" on by default).
NB. If required then you can later "squat" your app onto Catalyst with Squatting::On::Catalyst
There is also CGI::Ajax.