On the Pengines download and install page:
https://pengines.swi-prolog.org/docs/getting_started.html
Is the following text:
Start run.pl as ./run.pl on Unix or double-click run.pl on Windows...
This does not work on Linux, at least not on my Ubuntu 18.04 box. First, most Linux boxes try to run files with a pl extension as Perl scripts. Just to test, I did execute chmod +x run.pl and tried to run it. I got a slew of Perl launch errors.
Instead, I simply ran swipl with run.pl as the command line argument from the directory run.pl resides in (i.e. - the main Pengines directory):
swipl run.pl
Perhaps the docs should be updated to reflect this, with a note about making sure the swipl binary is in your environment PATH?