Arch Linux Bash script for diffing locally installed files with the current package version

pacman-filediff

#!/bin/bash
# Diff a file on the filesystem with the current package version
set -eu

file="${1:?No file specified}"
[ -e "$1" ]   || { >&2 printf 'Path does not exist: %s\n' "$1"; exit 1; }
[ ! -d "$1" ] || { >&2 printf 'Path is a directory: %s\n' "$1"; exit 2; }
# Canonicalize $file without resolving the basename
dir="$(readlink -f "$(dirname "$file")")"
file="$(basename "$file")"
case "$dir" in
  /) file="/${file}" ;;
  *) file="${dir}/${file}" ;;
esac

read -r package version < <(pacman -Fo "$file" | awk '/ is owned by /{print $5, $6}') || : # Allow non-zero exit for read

case "${package-}" in '') >&2 printf '%s does not appear to be owned by a repository package\n' "$file"; exit 3; esac

>&2 printf '%s is owned by %s %s\n' "$file" "$package" "$version"

pkgfile=/var/cache/pacman/pkg/${package#*/}-$version-x86_64.pkg.tar.xz
if [ ! -e "$pkgfile" ]; then
  >&2 printf 'Package %s is not cached, using "pacman -Sdw %s" to download it...\n' "$package" "${package#*/}"
  sudo pacman -Sdw --quiet --noconfirm "${package#*/}" >/dev/null
fi

diff --color=${COLOR:-always} -u <(tar -xf "$pkgfile" "${file#/}" -O 2>/dev/null) "$file" \
| tail -n+3 \
| perl -pne 'END { print(STDERR "Files are identical\n") if($. == 0); }'