cmd-ref: document data:status command (#3812)

* cmd-ref: document data:status command

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content/docs/command-reference/data/status.md

@@ -0,0 +1,135 @@
+# data status
+
+Show changes in the data tracked by DVC in the workspace.
+
+## Synopsis
+
+```usage
+usage: dvc data status [-h] [-q | -v]
+                       [--granular] [--unchanged]
+                       [--untracked-files [{no,all}]]
+                       [--json]
+```
+
+## Description
+
+The `data status` command displays the state of the working directory and the
+changes with respect to the last Git commit (`HEAD`). It shows you what new
+changes have been committed to DVC, which haven't been committed, which files
+aren't being tracked by DVC and Git, and what files are missing from the
+<abbr>cache</abbr>.
+
+The `dvc data status` command only outputs information, it won't modify or
+change anything in your working directory. It's a good practice to check the
+state of your repository before doing `dvc commit` or `git commit` so that you
+don't accidentally commit something you don't mean to.
+
+An example output might look something like follows:
+
+```dvc
+$ dvc data status
+Not in cache:
+  (use "dvc fetch <file>..." to download files)
+        data/data.xml
+
+DVC committed changes:
+  (git commit the corresponding dvc files to update the repo)
+        modified: data/features/
+
+DVC uncommitted changes:
+  (use "dvc commit <file>..." to track changes)
+  (use "dvc checkout <file>..." to discard changes)
+        deleted: model.pkl
+(there are other changes not tracked by dvc, use "git status" to see)
+```
+
+As shown above, the `dvc data status` displays changes in multiple categories:
+
+- _Not in cache_ indicates that the hash for files are recorded in `dvc.lock`
+  and `.dvc` files but the corresponding cache files are missing.
+- _DVC committed changes_ indicates that there are changes that are
+  `dvc-commit`-ed that differs with the last Git commit. There might be more
+  detailed state on how each of those files changed: _added_, _modified_,
+  _deleted_ and _unknown_.
+- _DVC uncommitted changes_ indicates that there are changes in the working
+  directory that are not `dvc commit`-ed yet. Same as _DVC committed changes_,
+  there might be more detailed state on how each of those files changed.
+- _Untracked files_ shows the files that are not being tracked by DVC and Git.
+  This is disabled by default, unless [`--untracked-files`](#--untracked-files)
+  is specified.
+- _DVC Unchanged files_ shows the files that are not changed. This is not shown
+  by default, unless [`--unchanged`](#--unchanged) is specified.
+
+By default, `dvc data status` does not show individual changes inside the
+tracked directories, which can be enabled with [`--granular`](#--granular)
+option.
+
+## Options
+
+- `--granular` - show granular, file-level information of the changes for
+  DVC-tracked directories. By default, `dvc data status` does not show
+  individual changes for files inside the tracked directories.
+
+- `--untracked-files` - show files that are not being tracked by DVC and Git.
+
+- `--unchanged` - show unchanged DVC-tracked files.
+
+- `--json` - prints the command's output in easily parsable JSON format, instead
+  of a human-readable output.
+
+- `-h`, `--help` - prints the usage/help message, and exit.
+
+- `-q`, `--quiet` - do not write anything to standard output.
+
+- `-v`, `--verbose` - displays detailed tracing information.
+
+## Examples
+
+```dvc
+$ dvc data status
+Not in cache:
+  (use "dvc fetch <file>..." to download files)
+        data/data.xml
+
+DVC committed changes:
+  (git commit the corresponding dvc files to update the repo)
+        modified: data/features/
+
+DVC uncommitted changes:
+  (use "dvc commit <file>..." to track changes)
+  (use "dvc checkout <file>..." to discard changes)
+        deleted: model.pkl
+(there are other changes not tracked by dvc, use "git status" to see)
+```
+
+This shows that the `data/data.xml` is missing from the cache, `data/features/`
+a directory, has changes that are being tracked by DVC but is not Git committed
+yet, and a file `model.pkl` has been deleted from the workspace. The
+`data/features/` directory is modified, but there is no further details to what
+changed inside. The `--granular` option can provide more information on that.
+
+## Example: Granular output
+
+Following on from the above example, using `--granular` will show file-level
+information for the changes:
+
+```dvc
+$ dvc data status --granular
+Not in cache:
+  (use "dvc fetch <file>..." to download files)
+        data/data.xml
+
+DVC committed changes:
+  (git commit the corresponding dvc files to update the repo)
+        added: data/features/foo
+
+DVC uncommitted changes:
+  (use "dvc commit <file>..." to track changes)
+  (use "dvc checkout <file>..." to discard changes)
+        deleted: model.pkl
+(there are other changes not tracked by dvc, use "git status" to see)
+```
+
+Now there's more information in _DVC committed changes_ regarding the changes in
+`data/features`. From the output, it shows that there is a new file added to
+`data/features`: `data/features/foo`.

content/docs/sidebar.json

@@ -215,6 +215,17 @@
         "label": "dag",
         "slug": "dag"
       },
+      {
+        "label": "data",
+        "slug": "data",
+        "source": false,
+        "children": [
+          {
+            "label": "data status",
+            "slug": "status"
+          }
+        ]
+      },
       {
         "label": "destroy",
         "slug": "destroy"