update

technology/applications/cli/unionfarm.md

@@ -0,0 +1,54 @@
+---
+obj: application
+repo: https://codeberg.org/chrysn/unionfarm
+rev: 2025-01-30
+---
+
+# unionfarm
+This is a small utility for managing symlink farms. It takes a "farm" directory and any number of "data" directories, and creates (or updates) the union (or overlay) of the data directories in the farm directory by placing symlinks to data directories.
+
+It is similar to
+- union mounts (overlay/overlayfs) -- but works without system privileges; it is not live, but can then again err out on duplicate files rather than picking the highest ranking
+
+Usage: `unionfarm <FARM> [DATA]...`
+
+## Example
+
+```
+$ tree my-photos
+my-photos
+├── 2018/
+│   └── Rome/
+│       └── ...
+└── 2019/
+    └── Helsinki/
+        └── DSCN2305.jpg
+```
+
+Assume you have a collection of photos as above, and want to see them overlaid with a friend's photos:
+
+```
+$ tree ~friend/photos
+/home/friend/photos
+├── 2018/
+│   └── Amsterdam/
+│       └── ...
+└── 2019/
+    └── Helsinki/
+        └── DSC_0815.jpg
+```
+
+With unionfarm, you can create a shared view on them:
+
+```
+$ unionfarm all-photos my-photos ~friend/photos
+$ tree all-photos
+all-photos
+├── 2018/
+│   ├── Amsterdam -> /home/friend/photos/2018/Amsterdam/
+│   └── Rome -> ../../my-photos/2018/Rome/
+└── 2019/
+    └── Helsinki/
+        ├── DSC_0815.jpg -> /home/friend/photos/2019/Helsinki/DSC_0815.jpg
+        └── DSCN2305.jpg -> ../../../my-photos/2019/Helsinki/DSCN2305.jpg
+```