> Can I use a bash script to accept input from a HTML form?
You can use bash via CGI. I'd try to avoid it in favour of something with more extensively tested CGI libraries though (Perl for example).
> I want to do this just on my computer, not on a web server.
You need a webserver (or a plugin for a web browser) - but that is just a piece of software, it doesn't have to be a dedicated machine. I'm fond of http://www.lighttpd.net/ and a popular choice is http://httpd.apache.org/