It seems, You can't get
PTBatcher command line tool anymore. That tool is declared obsolete and removed since version 2014. See the release note for version 2014 here However, some new command line alternatives have been added. Those are
You can use
PTBatcherGUI tool instead. It has BatchProcessing support.
You can get that installing
hugin. Do it in a terminal with the command
sudo apt install hugin
But the package in Ubuntu repository for Xenial is old (version 2015). You can get a more recent version by using
hugin/hugin-builds PPA. From PPA description page, the builds are fairly stable.
sudo add-apt-repository ppa:hugin/hugin-builds
sudo apt-get update
sudo apt-get install hugin
You can also use some of the techniques described in these pages for command line processing