Then the script needs to print a specific line and specfic characters of that line into a variable.

What do you mean that?

So the script needs to find the field name and record it.

So use the method that returns a list of field names?

https://metacpan.org/pod/WWW::Mechanize#mech-current_form, https://metacpan.org/pod/WWW::Mechanize#forms, https://metacpan.org/pod/HTML::Form#names-form-param