CopyScore

A tiny, pure‑Bash utility that answers the question:

“How much of Repo B was copied from Repo A?”

CopyScore walks both directories, compares every text file line‑by‑line, and prints:

Per‑file similarity %
Weighted (line‑level) similarity %
Average of file similarities %

Designed for macOS’ default Bash 3.2 — no Homebrew, Python, or GNU coreutils required. It also runs on any POSIX shell with standard utilities (find, awk, sort, comm, …).

Why this exists

When evaluating open‑source reuse, most diff tools highlight differences. CopyScore flips the lens and shows a quantitative similarity score you can drop into an email, slide deck, or diligence report.

Quick start

# 1. clone
$ git clone https://github.com/jacobshea/copyscore.git
$ cd copyscore

# 2. make executable
$ chmod +x copyscore.sh

# 3. compare two repos (defaults to every text file)
$ ./copyscore.sh path/to/original path/to/suspect

Example output:

Comparing folders:
  Original: /Users/jacob/repo_original
  Suspect:  /Users/jacob/repo_suspect

File‑by‑file comparison:
------------------------
package.json                  → 74%  
src/lib/utils.ts              → 95%  
src/components/ui/button.vue  → 100%

Summary:
---------
Average file similarity:   91%
Line‑weighted similarity:  94%

CLI options

Flag	Purpose	Example
(none)	Scan all text files (default)	`./copyscore.sh repoA repoB`
`-e ts,vue,md`	Comma‑separated extension list → restrict scan	`-e ts,vue`
`-x node_modules,tests`	Ignore paths whose relative prefix matches	`-x node_modules -x .git`
`-t 80`	Only report files ≥ 80 % similar	–
`-o report.csv`	Save per‑file results to CSV	–
`-j report.json`	Save per‑file results to JSON	–

Examples

# Only TS/Vue files, skip node_modules, CSV + JSON exports
./copyscore.sh -e ts,vue -x node_modules -o stats.csv -j stats.json repoA repoB

# Show just the really‑close matches (≥90 %)
./copyscore.sh -t 90 repoA repoB

Features

All‑text default – zero flags gives you the whole picture.
Add -e to narrow if you know which languages matter.
Pure Bash (3.2‑safe) – runs on fresh macOS without brew install sprawl.
Whitespace‑agnostic & order‑independent – trims spaces and sorts lines so re‑ordering doesn’t hide copying.
Colorized terminal output – green ≥90 %, yellow 50‑89 %, red <50 % (auto‑disables when piped).
CSV and JSON export – ready for spreadsheets or scripts.
Ignore paths – drop node_modules, dist, tests, etc.
Similarity threshold – sift noise with -t.

Limitations & future ideas

Path‑exact matching – a file is compared only when paths match in both repos. (Workaround: rsync -rvn or rename beforehand.)
Binary files ignored – comparisons are text‑only.
Context lost – sorting lines kills diff context; great for plagiarism detection, not for patch generation.
Performance – fine for small/medium repos (< 100k LOC). Large mono‑repos will be slower.

Roadmap

Verbose/debug mode (-V) to show exactly which files were included or skipped.
Glob‑style ignore patterns (e.g. -X "node_modules/**").
Tiny fixture test‑suite (Bats) for CI.
Optional parallel mode (xargs -P).

Contributing

PRs are welcome — please keep POSIX compliance in mind (BSD vs GNU flags).

Fork & create a branch
Make your changes
Open a PR explaining the improvement

Thanks for helping improve CopyScore!

License

MIT — free to use, modify, and embed in your own investigative toolchain.

jacobshea/compare_two_folders