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##### 3.17.5.1 Rule Variables

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.