I am trying to call the executable of a program ( ObjC) ( Very simple ) called 16.1 from the command line with these commands. ( Given that the following is in a terminal window) MB-Pro Debug m$ pwd /Users/m/Xcode_practise/16.1/build/Debug MB-Pro Debug m$ ls -F 16.1* MB-Pro Debug m$ /Users/m/Xcode_practise/16.1/build/Debug/16.1 2009-02-11 20:51:09.918 16.1[499:10b] Hello, World! MB-Pro Debug m$ 16.1 -bash: 16.1 command not found So, if I am correct, I am in the PWD when calling the executable, but it only responds to the full - path. Could someone perhaps explain why this is so, in other words, why the invocation "16.1" will not work? Thanks as usual in advance.