|git-annex-diffdriver(1)||General Commands Manual||git-annex-diffdriver(1)|
To use this, you will need to have installed some git external diff driver command. This is not the regular diff command; it takes a git-specific input. See git's documentation of GIT_EXTERNAL_DIFF and gitattributes(5)'s documentation of external diff drivers.
Configure git to use "git-annex diffdriver -- cmd params --" as the external diff driver, where cmd is the external diff driver you want it to run, and params are any extra parameters to pass to it. Note the trailing "--", which is required.
For example, set GIT_EXTERNAL_DIFF=git-annex diffdriver -- j-c-diff --