>>
>> But I don't know how to get the *content* of the file being submitted to run
>> my syntax check rules against it !
>>
> git log -p <old>..<new>
> git diff <old>..<new>
or in case of the tool requiring a full worktree
mkdir /tmp/test
GIT_WORKTREE=/tmp/test git checkout -f <new>
and then perform the check on that full tree?