file-syncer

Utility for syncing files -- mainly live-sync of folder symlinks to hardlinks. (for Docker and other stubborn tools)

Install

> Note: Installation is not necessary if using npx file-syncer to run.

``
yarn add file-syncer # or: npm i file-syncer
`

General usage

`
// basic
npx file-syncer --from XXX YYY ZZZ --to HardLinked [--watch] [--async] [--autoKill] [etc...]

// node-modules
npx file-syncer --from node_modules/XXX "node_modules/spa ces" --to HardLinked
`

Run npx file-syncer --help for more details. (or check the option list in the source code)

Docker example

From: https://stackoverflow.com/a/68765508

Given the existing directory structure:
`
parent_dir
- common_files
- file.txt
- my-app
- Dockerfile
- common_files -> symlink to ../common_files
`

Basic usage:
`
cd parent_dir

// starts live-sync of files under "common_files" to "my-app/HardLinked/common_files"
npx file-syncer --from common_files --to my-app/HardLinked
`

Then in your Dockerfile:
`
[regular commands here...]

have docker copy/overlay the HardLinked folder's contents (common_files) into my-app itself


COPY HardLinked /
`

Q/A

* How is this better than just copying parent_dir/common-files to parent_dir/my-app/common_files before Docker runs?
> That would mean giving up the regular symlink, which would be a loss, since symlinks are helpful and work fine with most tools. For example, it would mean you can't see/edit the source files of common_files from the in-my-app copy, which has some drawbacks. (see below)

* How is this better than copying parent_dir/common-files to parent_dir/my-app/common_files_Copy before Docker runs, then having Docker copy that over to parent_dir/my-app/common_files at build time?
> There are two advantages:
> 1) file-syncer does not "copy" the files in the regular sense. Rather, it creates hard links from the source folder's files. This means that if you edit the files under parent_dir/my-app/HardLinked/common_files, the files under parent_dir/common_files are instantly updated, and vice-versa, because they reference the same file/inode. (this can be helpful for debugging purposes and cross-project editing [especially if the folders you are syncing are symlinked node-modules that you're actively editing], and ensures that your version of the files is always in-sync/identical-to the source files)
> 2) Because file-syncer only updates the hard-link files for the exact files that get changed, file-watcher tools like Tilt or Skaffold detect changes for the minimal set of files, which can mean faster live-update-push times than you'd get with a basic "copy whole folder on file change" tool would.

* How is this better than a regular file-sync tool like Syncthing?
> Some of those tools may be usable, but most have issues of one kind or another. The most common one is that the tool either cannot produce hard-links of existing files, or it's unable to "push an update" for a file that is already hard-linked (since hard-linked files do not notify file-watchers of their changes automatically, if the edited-at and watched-at paths differ). Another is that many of these sync tools are not designed for instant responding, and/or do not have run flags that make them easy to use in restricted build tools. (eg. for Tilt, the --async flag of file-syncer enables it to be used in a local(...) invokation in the project's Tiltfile`)

Tasks

1) Add better documentation.