Are you confusing memory and storage space?

Yes - I mean disk storage space rather than RAM.

You don't say which models pi are involved

Raspberry Pi Zero with just 512Mb RAM - but both units have the same amount of RAM.

Did you forget about this?

I did look at cpanm but it isn't installed, so I have not been using it. I have today tried installing it with sudo apt-get install cpanm which didn't work and with cpan APP::cpanminus which was 'Killed'.

What needs doing to install and use cpanm?

Ignoring the fact that the first thing you did after running cpan was to install cpan, go back and read what I wrote :) If you run out of RAM expect daft things to happen. Use the OS package management to install things, you don't need to everything yourself. sudo apt install libhttp-server-simple-perl You're wasting time compiling on a low end/embedded system. apt isn't cpan, so don't expect packages to be the same as they do on cpan, which is probably why your apt-get install cpanm "didn't work" (this isn't a report anyone can help you with constructively :), sudo apt install cpanminus or something similar. Also The documentation often has hints and tips for installation.

Update: fixed autocorrect based typo.

Use the OS package management to install things, you don't need to everything yourself. sudo apt install libhttp-server-simple-perl You're wasting time compiling on a low end/embedded system. apt isn't cpan, so don't expect packages to be the same as they do on cpan

Thank you so much marto.

I have managed to get the server working with sudo apt install libhttp-server-simple-perl. I had no idea that there was any way to install a Perl module other than writing it yourself, copying the Perl code for pure Perl modules or using cpan.

Where would I look to find what can be installed using apt and what package name to use?