How to restore the permissions of files and directories within git if they have been modified?

I have a git checkout. All the file permissions are different than what git thinks they should be therefore they all show up as modified.

Without touching the content of the files (just want to modify the permissions) how do I set all the files permissions to what git thinks they should be?

Git keeps track of filepermission and exposes permission changes when creating patches using git diff -p. So all we need is:

1. create a reverse patch
2. include only the permission changes
3. apply the patch to our working copy

As a one-liner (run from the repository's root directory):

git diff -p -R --no-ext-diff --no-color --diff-filter=M \
    | grep -E "^(diff|(old|new) mode)" --color=never  \
    | git apply

you can also add it as an alias to your git config...

git config --global --add alias.permission-reset '!git diff -p -R --no-ext-diff --no-color --diff-filter=M | grep -E "^(diff|(old|new) mode)" --color=never | git apply'

...and you can invoke it via:

git permission-reset

Note, if you shell is bash, make sure to use ' instead of " quotes around the !git, otherwise it gets substituted with the last git command you ran.

Thx to @Mixologic for pointing out that by simply using -R on git diff, the cumbersome sed command is no longer required.