Hello, I managed to have perl 5.6 on Ubuntu 18.04.1. I'm doing 2 things :

• Use patchperl (just mandatory when you want to build old perl on recent distributions)
• Add the -lm to the cc -o miniperl ... (in the middle of the make step) - we add it through the configure script (-Alibs='-lm')

wget https://www.cpan.org/src/5.0/perl-5.6.2.tar.gz
tar xvzf perl-5.6.2.tar.gz
sudo cpanm Devel::PatchPerl
patchperl perl-5.6.2
cd perl-5.6.2
./Configure -des -Dprefix=/opt/perl5.6 -Aldflags='-lm'
make 
sudo make install
[download]

Hope it will help you (if you don't want to use perlbrew).


Rgds,

Thibault