commit 223b88afd7cf94abafd08642e8f0fae8dfdc05a3
Author: Darren 'Tadgy' Austin <darren@afterdark.org.uk>
Date:   Sat Dec 16 20:01:26 2023 +0000

    Add gitattributesdb git hook script.

diff --git a/gitattributsdb b/gitattributsdb
new file mode 100755
index 0000000..1e0f3e8
--- /dev/null
+++ b/gitattributsdb
@@ -0,0 +1,192 @@
+#!/usr/bin/env bash
+# Version: 0.0.2
+# Copyright (c) 2023:
+#   Darren 'Tadgy' Austin <darren (at) afterdark.org.uk>
+# Licensed under the terms of the GNU General Public License version 3.
+
+# Defaults.
+DB_FILE=".gitattributsdb"		# Database file, relative to the repository root.
+DB_EXTRA=".gitattributsdb-extra"	# List of base64 encoded filenames (one per line) to also store/restore attributes for.
+					# To add entries to this file, use: printf "%s" "<filename>" | base64 -w 0 >>.gitattributsdb-extra
+					# Where '<filename>' is relative to the repository root.
+
+# Variables.
+declare -A DB_OWNERSHIPS DB_MODES DB_ACLS
+# shellcheck disable=SC2155
+declare PLATFORM="$(uname -s)"
+
+# Function to output a log/info message.
+log() {
+  printf "%s: %s\\n" "${0##*/}" "$*"
+}
+
+# Function to output a warning message to stderr.
+warn() {
+  log "Warning:" "$*" >&2
+}
+
+# Function to output an error message to stderr and die.
+error() {
+  log "Error:" "$*" >&2
+  exit 1
+}
+
+# Function to display help.
+show_help() {
+  local SCRIPT="${0##*/}"
+
+	#........1.........2.........3.........4.........5.........6.........7.........8
+  cat <<-EOF
+	Usage: $SCRIPT [options] <hook name>
+	Store and restore file attributes for files within the git repository from a
+	database stored within the repository itself.
+
+	This program is intended to be called from git hooks, rather than directly.
+
+	# FIXME: Write some info about using as a submodule and as a hook in .githooks/.
+	EOF
+}
+
+# Function to read the database into an array.
+read_db() {
+  local FILENAME MODE OWNERSHIP ACL
+
+  # Do nothing if the DB file doesn't exist.
+  [[ ! -e "$DB_FILE" ]] && return 0
+
+  # Read the file.
+  while read -r FILENAME OWNERSHIP MODE ACL; do
+    # Store the attributes in arrays.
+    DB_OWNERSHIPS[$FILENAME]="$OWNERSHIP"
+    DB_MODES[$FILENAME]="$MODE"
+    DB_ACLS[$FILENAME]="$ACL"
+  done < <(grep -Ev '^(#|$)' "$DB_FILE")
+
+  return 0
+}
+
+# Function to store file attributes into the database.
+store_attributes() {
+  local COUNT=0 DB_TMP FILE X
+
+  # Informational message.
+  log "Storing file attributes into database"
+
+  # Use a temporary file for the new database.
+  DB_TMP="$(mktmp "$DB_FILE.XXXXXX" 2>/dev/null)" || error "Failed to create temporary database file"
+
+  # While Darwin supports ACLs, there is no standard output and input format for them - don't even try.
+  [[ "$PLATFORM" == "Darwin" ]] && warn "Not storing ACLs on Darwin"
+
+  # File header.
+  printf "# %s\\n" "This is the gitattributsdb database file." >"$DB_TMP"
+  printf "# %s\\n\\n" "Do not manually edit this file - any changes will be overwritten." >>"$DB_TMP"
+
+  # Create the database.
+  while read -r -d $'\0' FILE; do
+    # No need to process the database files themselves.
+    [[ "$FILE" == "$DB_FILE" ]] || [[ "$FILE" == "$DB_EXTRA" ]] && continue
+
+    if [[ "$PLATFORM" == "Linux" ]]; then
+      # On Linux, we can handle ACLs too.
+      printf "%s %s %s\\n" "$(printf "%s" "$FILE" | base64 -w 0 2>/dev/null)" "$(stat --printf '%U:%G %.4a' -- "$FILE" 2>/dev/null)" \
+          "$(getfacl -cEsp -- "$FILE" 2>/dev/null | base64 -w 0 2>/dev/null)" >>"$DB_TMP"
+    elif [[ "$PLATFORM" == "Darwin" ]]; then
+      # Darwin just has to be different.
+      # Use the full path to Darwin's stat, in case there's a macports/brew/etc version installed.
+      printf "%s %s\\n" "$(printf "%s" "$FILE" | base64 2>/dev/null)" "$(/usr/bin/stat -f "%Su:%Sg %Mp%Lp" -- "$FILE" 2>/dev/null)" >>"$DB_TMP"
+    fi
+
+    (( COUNT++ ))
+  done < <(git ls-files -z --full-name -- . 2>/dev/null; while read -r X; do printf "%s\\0" "$(printf "%s" "$X" | base64 -d 2>/dev/null)"; done < \
+      <(grep -Ev '^(#|$)' "$DB_EXTRA" 2>/dev/null))
+
+  # Move the temporary file into place.
+  mv -- "$DB_TMP" "$DB_FILE" 2>/dev/null || { rm -f -- "$DB_TMP"; error "Failed to move database temporary file into place"; }
+
+  info "$COUNT entries stored"
+
+  # Add the databases themselves to the commit.
+  git add --all -f -- "$DB_EXTRA" 2>/dev/null	# OK to fail silently.
+  git add --all -f -- "$DB_FILE" 2>/dev/null || error "Failed to add database files to commit"
+
+  return 0
+}
+
+# Function to restore file attributes from the database.
+restore_attributes() {
+  local COUNT=0 FILE ID
+
+  # Informational message.
+  log "Restoring file attributes from database"
+
+  # Read the database.
+  read_db
+
+  # While Darwin supports ACLs, there is no standard output and input format for them - don't even try.
+  [[ "$PLATFORM" == "Darwin" ]] && warn "Not restoring ACLs on Darwin"
+
+  # Restore from the read database.
+  while read -r ID; do
+    # Decode the filename from the array ID.
+    FILE="$(printf "%s" "$ID" | base64 -d 2>/dev/null)" || { warn "Failed to decode filename: $ID"; continue; }
+
+    # Ignore empty filenames, or non-existant files.
+    [[ -z "$FILE" ]] || [[ ! -e "$FILE" ]] && continue
+
+    # Don't restore attributes for symlinks.
+    [[ -L "$FILE" ]] && warn "Not restoring attributes for symlink: $FILE" && continue
+
+    # Restore ownerships.
+    chown -- "${DB_OWNERSHIPS[$ID]}" "$FILE" 2>/dev/null || warn "Failed to restore ownership: $FILE"
+
+    # Store mode.
+    chmod -- "${DB_MODES[$ID]}" "$FILE" 2>/dev/null || warn "Failed to restore permissions: $FILE"
+
+    # Restore ACLs on Linux.
+    [[ "$PLATFORM" == "Linux" ]] && {
+      printf "%s" "${DB_ACLS[$ID]}" | base64 -d 2>/dev/null | setfacl -M - "$FILE" 2>/dev/null || warn "Failed to restore ACL: $FILE"
+    }
+
+    (( COUNT++ ))
+  done < <(printf "%s\\n" "${!DB_OWNERSHIPS[@]}")
+
+  info "$COUNT entries restored"
+
+  return 0
+}
+
+# Exit if bash isn't v4+.
+(( BASH_VERSINFO[0] < 4 )) && error "Bash v4 or later is required"
+
+# Change to the root directory of the repository.
+REPO_ROOT="$(git rev-parse --show-toplevel 2>/dev/null)"
+[[ -z "$REPO_ROOT" ]] && error "Could not determine git repository root"
+pushd -- "$REPO_ROOT" >/dev/null 2>&1 || error "Failed to switch to git repository root"
+
+# Parse command line.
+(( $# == 0 )) && {
+  printf "%s: %s\\n" "${0##*/}" "missing argument" >&2
+  printf "%s: %s %s\\n" "Try" "${0##*/}" "--help" >&2
+  exit 1
+}
+case "$1" in
+  '-h'|'--h'|'--help')
+    show_help
+    ;;
+  'post-checkout'|'post-merge')
+    # Restore the file attributes from the database.
+    restore_attributes
+    ;;
+  'pre-commit')
+    # Store the file attributes into the database.
+    store_attributes
+    ;;
+  *)
+    printf "%s: %s: %s\\n" "${0##*/}" "invalid option" "$1" >&2
+    printf "%s: %s %s\\n" "Try" "${0##*/}" "--help" >&2
+    exit 1
+    ;;
+esac
+
+exit 0