Without the url= parameter it launches a subprocess as
perl -MDBI::Gofer::Transport::stream -e run_stdio_hex
and feeds requests into it and reads responses from it. But thats not very useful.
With a url=ssh:firstname.lastname@example.org parameter it uses ssh to launch the subprocess
on a remote system. Thats much more useful!
It gives you secure remote access to DBI databases on any system you can login to.
Using ssh also gives you optional compression and many other features (see the
ssh manual for how to configure that and many other options via ~/.ssh/config file).
The actual command invoked is something like:
ssh -xq ssh:email@example.com bash -c $setup $run
where $run is the command shown above, and $command is
. .bash_profile 2>/dev/null || . .bash_login 2>/dev/null || . .profile 2>/dev/null; exec "$@"
which is trying (in a limited and fairly unportable way) to setup the environment
(PATH, PERL5LIB etc) as it would be if you had logged in to that system.
The "perl" used in the command will default to the value of $^X when not using ssh.
On most systems thats the full path to the perl thats currently executing.