Most programs write their results, including PostScript plots, to standard output. The exceptions are those which may create binary netCDF grd-files such as surface (due to the design of netCDF a filename must be provided; however, alternative binary output formats allowing piping are available; see Section 4.17). With UNIX you can redirect standard output to a file or pipe it into another process. Error messages, usage messages, and verbose comments are written to standard error in all cases. You can use UNIX to redirect standard error as well, if you want to create a log file of what you are doing.