File association is used to determine what program
to use to open a file. All the file associations for
Ranger can be found in
~/.config/ranger/rifle.conf file. This file is well
documented and should answer most of your queries. Note that the file is
read from top to bottom and the rule that matches first is chosen and
applied.
In Ranger, you can choose a program to open a file based on its
extension. For example, to open a JPEG file with Feh image viewer, add
this line at the top of rifle.conf:
ext jpg = feh "$@"
After the specific file associations, I like to have a rule to catch
all the rest of the files and open them using xdg-open:
has xdg-open, flag f = xdg-open "$1"
For more info on configuring Ranger, refer to the excellent documentation by Arch here.
Tried with: Ranger 1.6.1 and Ubuntu 14.04