Command line processing order To understand how command lines are processed it is necessary to know the order in which operations occur. When you have typed in a line and pressed the return key the following things happen: 1. Multiple commands, separated by ‘!’ characters are separated for individual processing. 2. Any comments (indicated by semicolons) are removed. 3. The ‘ ’, ‘>>’, ‘}’ and ‘}}’ commands are searched for and interpreted. Any necesary file creation or opening is done and the redirection part of the command line is stripped off. 4. All wildcards are expanded and inserted into the command line in place of any prototypes. 5.
The system attempts to match the command name (the first word on the command line) with one of the current memory resident drivers. If a match is found the MRD is called. Otherwise a search is made of the inbuilt com- mands. If a match is found the syntax of any arguments is checked with that which the particular command requires. If no error is detected the command is executed. 6. If the command is not an MRD or an inbuilt one, the system assumes that you are executing a file whose name is the same as the specified command, with .xrel , .shell , or .exec added.
A search is made in the current directory, and in all the directories specified in your execution path (see the xpath command), for one of these three files. Command Handling User Tutorial Manual Page 29