in reply to cgi HTML head error

On a shared host where you have a cgi-bin directory, start off with a simple script. It doesn't even need to be Perl - it could be anything that prints to STDOUT and is executable.

The minimal response from any of these programs is this, 

Status: 200
Content-type: text/html

<!doctype html>
<html> HTML Goes Here </html>

[download]

See https://www.perl.com/article/perl-and-cgi/. I also recommend checking out CGI::Tiny. If you're on a shared host that's "powered" by cPanel/WHM, then you can likely install Perl modules locally via the cPanel interface (ask your host if you don't know). There's also cpanm coupled with local::lib.

In Section Seekers of Perl Wisdom