Gnus uses rule variables to decide how to view a file. All these variables are of the form
(list '(regexp1 command2)
'(regexp2 command2)
...)
gnus-uu-user-view-rules ¶This variable is consulted first when viewing files. If you wish to use,
for instance, sox to convert an .au sound file, you could
say something like:
(setq gnus-uu-user-view-rules
(list '("\\\\.au$" "sox %s -t .aiff > /dev/audio")))
gnus-uu-user-view-rules-end ¶This variable is consulted if Gnus couldn’t make any matches from the user and default view rules.
gnus-uu-user-archive-rules ¶This variable can be used to say what commands should be used to unpack archives.