" Quotes areusedtoremove thespecialmeaningofallothercharacters ! A separator between multiple commands > >> Standard output redirection } }} Standard error redirection Standard input | A pipe to connect two commands ^ Pipe standard error ; A comment separator & Run command asynchronously Redirect following lines until marker into input of command, within shell files only. The above are listed in order of precedence. Some examples: dir | cio | cio This performs a directory listing and passes the output through the cio command a couple of times. ssasm myfile.s ! type myfile.s >cent: & This will perform the assembly synchronously, then print the source file out as a background process.
ssasm myfile.s & ! type myfile.s > cent: & Both the assembly and the printing proceed asynchronously. "ssasm myfile.s ! type myfile.s > cent:" & Here both the assembly and the printing run in the background, but the printing will not start until the assembly has completed. The implications of multi-tasking for programs Having multi-tasking affects a program’s user interface. It is the responsibility of the programmer to attempt to ensure his or her programs can run in background, if the user so desires. In general, a program can not assume it has unlimited access to resources, particularly access to the keyboard or video.
Input and output should beviathestandardroutines,sotheycanbere-directed, neverdirecttothehardware. Wherever possible, a program should behave correctly, whether it is run syn- chronously or asynchronously. The isinteractive system call is provided for a process to tell whether or not it is running in the background. If it is a background process, it should produce no unnecessary output. It should not attempt to read from the keyboard, because that is being used for other processes. Multi Tasking User Tutorial Manual Page 61