cmd-ref: Document ls-url command (#3996)

* cmd-ref: Document ls-url command

* Update content/docs/command-reference/list-url.md

Co-authored-by: Dave Berenbaum <[email protected]>

* Use admonitions, consistently use list-url, fix usage

* Modify example headings

* Describe -R option consistently in list and list-url refs.

Fix inaccuracy: dvc ls -R does not print directories.

* update linked-terms.js

* Add links from get-url and import-url to list-url

* improve first paragraph in description

Co-authored-by: Jorge Orpinel <[email protected]>
Co-authored-by: Dave Berenbaum <[email protected]>
Co-authored-by: Thomas Kunwar <[email protected]>

content/docs/command-reference/get-url.md

@@ -31,6 +31,13 @@ while `out` can be used to specify the directory and/or file name desired for
 the downloaded data. If an existing directory is specified, then the file or
 directory will be placed inside.
 
+<admon type="tip">
+
+See `dvc list-url` for a way to browse the external location for files and
+directories to download.
+
+</admon>
+
 DVC supports several types of (local or) remote data sources (protocols):
 
 | Type      | Description                  | `url` format example                          |

content/docs/command-reference/import-url.md

@@ -52,6 +52,13 @@ The imported data is <abbr>cached</abbr>, and linked (or copied) to the current
 working directory with its original file name e.g. `data.txt` (or to a location
 provided with `out`).
 
+<admon type="tip">
+
+See `dvc list-url` for a way to browse the external location for files and
+directories to download.
+
+</admon>
+
 An _import `.dvc` file_ is created in the same location e.g. `data.txt.dvc` –
 similar to using `dvc add` after downloading the data. This makes it possible to
 update the import later, if the data source has changed (see `dvc update`).

content/docs/command-reference/list-url.md

@@ -0,0 +1,97 @@
+# list-url
+
+<admon type="info">
+
+Aliased to `dvc ls-url`
+
+</admon>
+
+List contents from a supported URL (for example `s3://`, `ssh://`, and other
+protocols).
+
+<admon type="tip">
+
+Useful to find data to `dvc get-url` or `dvc import-url`.
+
+</admon>
+
+## Synopsis
+
+```usage
+usage: dvc list-url [-h] [-q | -v] [-R] url
+
+positional arguments:
+  url              (See supported URLs in the description)
+```
+
+## Description
+
+Lists files and directories from an external location. `dvc list-url` provides a
+uniform interface to browse the contents of an external location using any
+protocol that is understood by `dvc get-url` or `dvc import-url`. For example,
+it is roughly equivalent to `aws s3 ls` when using the `s3://` protocol, or
+`ssh user@host ls -a` when using `ssh://`.
+
+The `url` argument specifies the location of the data to be listed. It supports
+several kinds of external data sources:
+
+| Type    | Description                  | `url` format example                  |
+| ------- | ---------------------------- | ------------------------------------- |
+| `s3`    | Amazon S3                    | `s3://bucket/data`                    |
+| `azure` | Microsoft Azure Blob Storage | `azure://container/data`              |
+| `gs`    | Google Cloud Storage         | `gs://bucket/data`                    |
+| `ssh`   | SSH server                   | `ssh://[email protected]/path/to/data` |
+| `local` | Local path                   | `/path/to/local/data`                 |
+
+<admon type="info">
+
+If you installed DVC via `pip` and plan to access cloud services as external
+data sources, you might need to install these optional dependencies: `[s3]`,
+`[azure]`, `[gs]`, `[oss]`, `[ssh]`. Alternatively, use `[all]` to include them
+all. The command should look like this: `pip install "dvc[s3]"`. (This example
+installs `boto3` library along with DVC to support S3 storage.)
+
+</admon>
+
+Only the root directory is listed by default, but the `-R` option can be used to
+list files recursively.
+
+## Options
+
+- `-R`, `--recursive` - recursively list files in all subdirectories.
+
+- `-h`, `--help` - prints the usage/help message, and exit.
+
+- `-q`, `--quiet` - do not write anything to standard output. Exit with 0 if no
+  problems arise, otherwise a non-zero value.
+
+- `-v`, `--verbose` - displays detailed tracing information.
+
+## Example: Amazon S3
+
+This command will list objects and common prefixes under the specified path:
+
+```dvc
+$ dvc list-url s3://bucket/path
+```
+
+DVC expects that AWS CLI is already
+[configured](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-configure.html).
+DVC will use the AWS credentials file to access S3.
+
+## Example: SSH
+
+```dvc
+$ dvc list-url ssh://[email protected]/path/to/data
+```
+
+Using default SSH credentials, the above command lists files and directories
+inside `data`.
+
+## Example: local file system
+
+```dvc
+$ dvc list-url /local/path/to/data
+```
+
+The above command will list the `/local/path/to/data` directory.

content/docs/command-reference/list.md

@@ -58,7 +58,7 @@ accessed with `dvc get`, `dvc import`, or `dvc.api`.
 
 ## Options
 
-- `-R`, `--recursive` - recursively prints contents of all subdirectories.
+- `-R`, `--recursive` - recursively list files in all subdirectories.
 
 - `--dvc-only` - show only DVC-tracked files and directories
   (<abbr>outputs</abbr>).
@@ -111,7 +111,7 @@ We can now, for example, download the model file with:
 $ dvc get https://github.com/iterative/example-get-started model.pkl
 ```
 
-## Example: List all files and directories in a data registry
+## Example: List all files in a data registry
 
 Let's imagine a DVC repo used as a
 [data registry](/doc/use-cases/data-registry#using-registries), structured with

content/docs/sidebar.json

@@ -323,6 +323,10 @@
         "label": "install",
         "slug": "install"
       },
+      {
+        "label": "list-url",
+        "slug": "list-url"
+      },
       {
         "label": "list",
         "slug": "list"

content/linked-terms.js

@@ -23,6 +23,10 @@ module.exports = [
     matches: 'dvc experiments',
     url: '/doc/command-reference/exp'
   },
+  {
+    matches: 'dvc ls-url',
+    url: '/doc/command-reference/list-url'
+  },
   {
     matches: 'dvc ls',
     url: '/doc/command-reference/list'