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Format Markdown with prettier in make fmt and fmt-check (closes #23)
`make fmt` now runs prettier over the Markdown files after the Go
formatters, and `make fmt-check` fails when prettier would change one.
`package.json`, `yarn.lock`, `.prettierrc` and `.prettierignore` are the
`sneak/prompts` copies at `dd4027b`, and both scripts find yarn the way
that repo's scripts do. `script/bootstrap` installs prettier with
`yarn install --frozen-lockfile`. When the yarn those scripts would run
is not 1.22.22, it installs yarn through corepack under node 22.17.0:
the node on `PATH` if it has that version, otherwise one installed
through nvm from a hash-checked archive. `README.md` and `TODO.md` are
reformatted once.

Model: opus-5-5
2026-10-06 08:36:58 +00:00

attrsum is a Go 1.22 command-line utility that adds, updates, verifies, and clears per-file file content checksums stored in extended attributes (xattrs) on macOS (APFS) and Linux, released under the WTFPL v2.

Original release 2025-05-08.

Current version 1.0 (2025-05-08).


Getting Started — Quick Build

# prerequisites: Go 1.22+
git clone https://git.eeqj.de/sneak/attrsum.git
cd attrsum
go build -o attrsum .

Install

go install git.eeqj.de/sneak/attrsum@latest   # into GOPATH/bin or $(go env GOBIN)

Semantic Versioning 2.0.0 is used for tags.


Usage

# add checksum & timestamp xattrs to every regular file under one or more paths
attrsum sum add DIR1 DIR2 file.txt

# update checksum only when file mtime is newer than stored sumtime
attrsum sum update DIR1 DIR2

# verify checksums, stop on first error
attrsum check DIR1 DIR2

# verify every file, reporting each result, keep going after errors
attrsum -v check --continue DIR1 DIR2

# remove checksum & timestamp xattrs
attrsum clear DIR1 DIR2

# read paths from stdin (use - as argument)
find /data -name "*.jpg" | attrsum sum add -

# quiet mode (suppress progress bar and summary)
attrsum -q sum add DIR
xattr key meaning
user.berlin.sneak.app.attrsum.checksum base-58 multihash (sha2-256)
user.berlin.sneak.app.attrsum.sumtime RFC 3339 timestamp of checksum

Flags:

  • -v, --verbose — per-file log output
  • -q, --quiet — suppress all output except errors (no progress bar or summary)
  • --exclude PATTERN — skip paths matching rsync/Doublestar glob
  • --exclude-dotfiles — skip any path component that starts with .

All commands display a progress bar with ETA and print a summary report to stderr on completion (unless --quiet is specified).

attrsum never follows symlinks and skips non-regular files (sockets, devices, …).


Why?

Apple APFS and Linux ext3/ext4 store no per-file content checksums, so silent data corruption can pass unnoticed. attrsum keeps a portable checksum inside each file’s xattrs, providing integrity verification that travels with the file itself—no external database required. Now you can trust a USB stick didn't eat your data.


TODO

Future improvements under consideration:

  • Dry-run mode (--dry-run, -n) — show what would be done without making changes
  • JSON output (--json) — machine-readable output for scripting and integration
  • Parallel processing (-j N) — use multiple goroutines for faster checksumming on large trees
  • Exit code documentation — formalize and document exit codes for scripting

Contributing

  • Author & maintainer: sneak – sneak@sneak.berlin
  • Issues / PRs: https://git.eeqj.de/sneak/attrsum/
  • Code must pass make check, which runs the tests and golangci-lint as phases of the Dockerfile (Docker is required) and checks formatting with gofmt for Go and prettier for Markdown. make bootstrap installs prettier, and make fmt fixes what the check reports.
  • No CLA; contributions are under WTFPL v2.

Community & Support

Bug tracker and wiki are in the Gitea repo linked above.

No formal Code of Conduct; be excellent to each other.


License

Everything is permitted. See WTFPL v2.

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