git-revert-file-permissions.sh

#!/bin/bash

# Git stores only the 'execute' file permission, and permissions sometimes gets lost
# when copying files around to/from Windows PCs or to/from FAT/FAT32 disk partitions.
#
# This script restores all file permissions to their original values in the Git repository.
# It is not as terse as the usual tips from the Internet, it will display
# the affected files.
#
# Limitations: This script does not attempt to properly parse the patch lines
#              generated by "git diff", therefore:
#              - It cannot cleanly display the affected files.
#              - It will probably fail if files have been renamed, and those renames
#                have not been checked in yet.
#
# Copyright (c) 2015 R. Diez - Licensed under the GNU AGPLv3.

set -o errexit
set -o nounset
set -o pipefail

# set -x  # Trace this script


# 1) Generate a patch with the current changes.
# Alternative to git diff -R below: revert the patch lines by piping to 'sed' like this:
#  | sed -e 's/^old/NEW/;s/^new/old/;s/^NEW/new/'
PATCH_LINES="$(git diff --patch -R)"

if false; then
  echo "PATCH_LINES: $PATCH_LINES"
fi


# 2) Keep only those patch lines about permission changes.
set +o errexit
PATCH_LINES_DIFF_AND_MODE="$(grep --extended-regexp '^(diff|old mode|new mode)' <<<"$PATCH_LINES")"
GREP_EXIT_CODE="$?"
set -o errexit

PATCH_LINES=""  # Release memory as soon as possible.

# Maybe there are no files to patch at all (no changes).
if [ $GREP_EXIT_CODE -eq 1 ]; then
  echo "No file permissions need to be reverted."
  exit 0
fi


# 3) Count the number of affected files. This is just for display purposes.
set +o errexit
FILE_COUNT="$(grep --count "old mode" <<<"$PATCH_LINES_DIFF_AND_MODE")"
GREP_EXIT_CODE="$?"
set -o errexit

if [ $GREP_EXIT_CODE -eq 1 ]; then
  echo "No file permissions need to be reverted."
  exit 0
fi


# 4) Display the affected files.
echo "Affected file(s) are (this script does not attempt to extract clean filenames):"

grep --before-context=1 "old mode" <<<"$PATCH_LINES_DIFF_AND_MODE" | grep --extended-regexp '^diff'


# 5) Revert the changes.
git apply <<<"$PATCH_LINES_DIFF_AND_MODE"
echo "Done reverting execute file permission on $FILE_COUNT file(s)."