Abstract: A shell program is used in conjunction with a computer that has a multitasking operating system. The shell program interprets sequences of commands, submitted as scripts, and passes the interpreted commands on to the operating system for execution. The shell program accepts scripts which define distinct sets of commands that are to be executed in parallel, and also accepts conditional commands that synchronize the execution of specified sets of commands with other specified sets of commands. Scripts are executed by the shell by creating a thread of execution for each set of commands that is to be executed in parallel with other sets of commands. All the threads created by the shell program share a common address space so that status information from the various threads, as well as computational results generated by these threads, can be used by other ones of the threads to synchronize the execution of such threads.