Using traditional unix shell scripting is not optimal for processing HTTP forms on the server-side, for a number of reasons.
Here is a reference to the programming languages used by the biggest web sites, hopefully you will find this useful:
Programming languages used in most popular websites
Also, if you look at the large Web CMS frameworks, like Wordpress, Joomla, Drupal, etc; most of them are written in PHP. I guess it is just a matter of time when we will start to see huge (highly popular, widely used) CMS frameworks in Python. If anyone knows of one, please post.
If you look at the largest site (Google), their web backend is mostly written in Python.
If you look at the second largest, Facebook, their back end language is most in PHP, followed by YouTube (again written in Python) and then Yahoo, written mostly in PHP.
So, I would consider either Python or PHP if you want to get into the nuts-and-bolts of writing web applications on the server side.
I don't know any top tier web site which uses shell scripts on the server side to process web requests (CGI); however, the list above does show that Amazon and Yahoo both user PERL, but PERL is also not a shell script; it is a programming language like PHP, Python, C#, etc.