Retrieving data from a form for sendmail

[Fred]

I enter data into a form and would like to have a single click button
to send mail to a user to advise them of the form data. Sendmail
let's me create a single command line that then is sent to a smtp
server. an attachment can also be created and attached to the email.
Any ideas on the best way to extract data from the form and put them
into a format that could be used by sendmail?

Thanks,
Fred