PostScript is an excellent page description language--but it does tend to be rather verbose. Compressing PostScript graphics files can reduce them by factor of five or more. For this reason, if a the name of an included PostScript file ends with `.Z' or `.gz', Dvips automatically runs `gzip -d'. For example:
\epsffile[72 72 540 720]{foo.ps.gz}
Since the results of such a command are not accessible to TeX, if you use this facility with the `epsf' macros, you need to supply the bounding box parameter yourself, as shown.
More generally, if the filename parameter to one of the graphics inclusion techniques starts with a left quote (``'), the parameter is instead interpreted as a command to execute that will send the actual file to standard output. For example:
\special{psfile="`gnuplot foo"}
to include the file `foo'. Of course, the command to be executed can be anything, including using a file conversion utility such as `tek2ps' or whatever is appropriate. This feature can be disabled with the `-R' command-line option or `R' configuration option.