patchrun

Command in, patch out.

Lots of commands rewrite your repo: package installs, code generators, codemods, formatters, framework CLIs, and whatever an AI assistant just suggested. Most of them have no dry-run flag. patchrun gives all of them the same one:

patchrun -- npx shadcn@latest add button

It runs the command in a throwaway copy of your repo and hands you back exactly what it changed, as a patch. Then you choose: apply, save, view, keep or discard.

How it works

1. Snapshot the repo into a detached Git worktree in a temp directory.
2. Replay your uncommitted changes (staged, unstaged and untracked) into it and commit them as a baseline.
3. Run the command there, with live output, and a pseudo-terminal for interactive scaffolders.
4. Diff the result against the baseline.

Step 2 is the clever bit. Because your own work-in-progress becomes the baseline, the diff contains only what the command did, and you can use patchrun on a dirty tree.

It is not a sandbox. The command still runs as you, with your permissions; patchrun only keeps it away from your working tree.

The details that make it scriptable

• If your repo changed while the command ran, patchrun checks before applying, with an optional 3-way fallback and a --check mode that writes nothing.
• --json output and documented exit codes (5: the command failed, 6: the patch didn't apply, 7: you discarded it, 9: timeout).
• Saved patches get a sidecar with the commit, command, exit code, duration and diffstat.
• A guard refuses to delete anything that isn't inside its own temp directory with the expected prefix.
• Tests inject real filesystem faults instead of using mocks.

That makes it a natural gate between an agent's proposed command and your working tree.

Status

Built over 14 and 15 May 2026: 12 commits, written with a coding agent and then hardened by hand. MIT. There are no releases yet, but it installs with Go:

go install github.com/alliecatowo/patchrun/cmd/patchrun@latest

Windows support is best-effort. The repo has example patches captured from a codemod, a prettier run and shadcn add button.