Is this the CGI forum?
I see you found it!
how do I call a CGI or perl function
This is pretty easy.
Your HTML doc will need a <form> to enter the list item and submit it to the server.
<form action="/cgi-bin/scriptname.cgi" method="post">
<input type="text" name="listitem">
<input type="submit" value="Upload list item">
This is all pretty self-explanitory. There are, of couse, other ways to submit the data, but this is the easiest.
Your script must now read the form data, open a file, and save it.
It should then return a new HTML doc with the updated list.
How do you want to do this?
I write in Perl, so if you want to have a go at writing a Perl script (basic Perl will be pretty simple with your knowledge of 'C'), then I can go though what you wrote and together we can get it up and running.
Does your server allow you to post CGI scripts?