An Operating Systems Vade Mecum

The command interpreter 245command interpreter 1command interpreter 1mailmailcommand interpreter 2command interpreter 2editoreditorcommand interpreter 3command interpreter 4compiler 1linkcompiler 2waitingfinishedactiveFigure 7.2 A tree of processeswith a physical name of a device or a file. The command interpreter can be in charge ofbinding these names. For example, a simulation program might call its inputsimulate.in and its output simulate.out. Perhaps the user wants to call thisprogram several times with different data. Instead of rewriting the program, the commandinterpreter could be used. One convention is to set the environment in a globalway:set associate simulate.in data.oneset associate simulate.out out.onesimulateset associate simulate.in data.twoset associate simulate.out out.twosimulateset associate simulate.in data.threeset associate simulate.out out.threesimulateIn this example, the simulation is run three times, each time under a different environment.An alternative is to list the input and output files as parameters to the Simulate program: