Thank you, Mojca and Aditya, for your comments and advice. It will take me, being no virtuoso with Terminal, a while to figure out what exactly I have to do. It is in my script that I will again run into problems and then I will beg you to help me out again.

Thank you, Hraban, for suggesting an easy way out: Use ConTeXt-Minimals, but also there I manage to run into problems, mainly with files and scripts that I can see in the finder but that are not found in Terminal, not even from their parent directory.  

Robert Blackstone