5 Starting Programs This section continues the discussion of commands, by expanding upon the treatment of "disk" files by 1616/OS . Obviously, the concepts here will be of most use when you start using programs that use the disk drives. The chapter includes starting a program, the different types of programs ( .exec and .xrel ), and dis- cussion of using shell files. Starting a program Starting a program is easy: you type its name, leaving off the extension. Programs can be identified by their extension, which is always .xrel , pronounced "dot exrel". Older programs are indentified by .exec .
Search path When the name of an executable program is typed in on the 1616/OS command line, and it does not refer to an executable memory-resident driver or an inbuilt com- mand, the system searches for a disk file to load and execute. It first searches your current directory for a file whose name is the command you typed with ‘ .xrel ’ added. It then searches for a file with ‘ .shell ’ added; If no ‘ .shell ’ file is found it searches for a file with ‘ .exec ’ added. As mentioned, the current directory is the one that appears in your prompt. If you have used the xpath command correctly, additional directories are searched.
If none of these three programs can be found in your current directory, then searching for these three files continues in other directories. The directories that are searched are as specified by your current execution search path, which is set using xpath . You can check for the current execution search path at any time simply by typing xpath . You specify which other directories are to be searched by using the xpath com- mand. In this manner, frequently used files can always be found, even when you are in some other directory. You should not include unwanted directories in your xpath commands, as this simply slows down access to programs.
Typically, you would include the command xpath /f0/bin /f0/utility or some similar sequence soon after starting the system. As an alternative, you can easily add directories to the search path by using xpath + /f0/newpath or similar at any time. Take care with xpath - , which removes all search paths. Starting Programs User Tutorial Manual Page 39