git diff(1) --shortstat "@{0 day ago}"
Show changes between commits, commit and working tree, etc
--shortstat
    Output only the last line of the --stat format containing total number of modified files, as well as
    number of added and deleted lines.
Show changes between the working tree and the index or a tree, changes between the index and a tree,
changes between two trees, or changes between two files on disk.
source manpages: git-diff