Shake is quite amazing: powered by Haskell, it's really easy to quickly throw together build rules for little problems that appear in everyday programming tasks.
Here's a small snippet of Shake rules that convert an SVG to an iOS application icon in the various required sizes. As a bonus point, it generates icons for different build configurations by showing and hiding layers using inkscape-export-layers. See this article for how to use the different icons sets.
-- Generate iOS icons from SVG
iosIcons :: String -> Rules ()
iosIcons target = do
let resolutions = [(29,[1,2,3]), (40,[1,2,3]), (50,[1,2]), (57,[1,2]), (60,[2,3]), (72,[1,2]), (76,[1,2])]
configurations = [Beta, Debug, Release]