lookback

lookback is a file and directory comparison tool. It answers two related questions:

• Are these two files the same? Hashes both files and compares the digests.
• Do these two directories contain the same files? Either compares file names and sizes (default), or hashes every file and compares the digests (full comparison mode). Optional -i flag ignores folder structure to focus exclusively on files (useful when directories have been moved around or renamed).

This is a cross-platform tool (macOS / Linux / Windows) written in Python and integrating the xxhash package for high-throughput hashing.

🚀 Installation

1. Install the uv package manager with the official installer (or brew install uv on macOS / Linux).

2. Install the tool:

uv tool install lookback

📖 Usage

Compare two files:

lookback <file1> <file2>

Compare two directories:

lookback <source> <destination>               # metadata only (filenames and file sizes)
lookback -f <source> <destination>            # full comparison mode: hash every file
lookback -i <source> <destination>            # ignore folder structure

Check that the destination contains all of the files from the source:

lookback <source> <destination> | grep "<"

Output uses a diff-like format. Lines starting with < are unique to the source side, > lines are unique to the destination side:

$ lookback /Volumes/PRJ_MST01 /Volumes/PRJ_BAK01
< 1432891  IMG_0421.dng
> 1432891  IMG_0422.dng

Other options (run lookback --help for full list):

  -f, --full                     : deep mode: hash every file (slower but safer)
  -i, --ignore                   : ignore folder structure (compare flat list of file names and sizes)
  -a, --algorithm [xxh64|xxh128] : hash algorithm (default: xxh64)
  -s, --save                     : save listing for manual comparison
  -X, --appledouble              : include AppleDouble (._*) files

🤝 Acknowledgments

A special thank you to Mohammad Ayyash for initiating me into the dark magic of Python and Bash, and writing the first "molist" commands from which this utility evolved.