Runs nix copy under the hood but only uploads paths that don't exist in upstream caches. It's async so may also be somewhat faster. Unlike nix copy, we also upload build dependencies. You may also pass the --recursive flag to absolutely not miss anything (be warned though, it queues up a lot of paths to check against upstream caches (also idk why you'd ever want to use this honestly)). Specify upstream caches to check against with --upstream-cache (can be specified multiple times, cache.nixos.org is always included).

Usage: nixcp [OPTIONS] --to <BINARY CACHE> <PACKAGE>

Arguments:
  <PACKAGE>  Package to upload to the binary cache

Options:
      --to <BINARY CACHE>
          Address of the binary cache (passed to nix copy --to)
  -u, --upstream-cache <UPSTREAM_CACHE>
          Upstream cache to check against. Can be specified multiple times. cache.nixos.org is always included
  -r, --recursive
          Whether to pass --recursive to nix path-info. Can queue a huge number of paths to upload
      --upstream-checker-concurrency <UPSTREAM_CHECKER_CONCURRENCY>
          Concurrent upstream cache checkers [default: 32]
      --uploader-concurrency <UPLOADER_CONCURRENCY>
          Concurrent uploaders [default: 16]
      --nix-store-concurrency <NIX_STORE_CONCURRENCY>
          Concurrent nix-store commands to run [default: 32]
  -h, --help
          Print help
  -V, --version
          Print version

Install with nix

nix profile install git+https://git.cy7.sh/cy/nixcp.git

Or run without installing:

nix run git+https://git.cy7.sh/cy/nixcp.git

Separate arguments with -- to pass them through to nixcp like so:

nix run git+https://git.cy7.sh/cy/nixcp.git -- --help