# Transferring data across docker or podman volumes

I often find myself starting temporary containers to transfer data between the local file-system and container volumes. Or sometimes, between volumes. And the entire process is a bit tedious. Starting a temporary container, mounting the volume, mounting the local file-system, and finally transferring the data.

So I made a python script which makes this easy. I call it `cvcp` - container volume cp (copy). It actually does not use `cp` though. It uses `rsync` for the data transfer. So it's necessary to have a container image with `rsync` installed.

You can find the script at https://github.com/jeet-parekh/cvcp. The repository also contains a `Dockerfile` which will build an image with `rsync` installed.

---

## Using cvcp

Download the file `cvcp` from the repository and place it inside your preferred path. I prefer `~/bin`.

Then, to use `cvcp`:

```bash
cvcp SOURCE DESTINATION
```

Path inside a container volume should be written as `<volume_name>:<path_inside_volume>`.

Either `SOURCE` or `DESTINATION` can be a local path or a path inside a container volume. Note however that both `SOURCE` and `DESTINATION` cannot be local paths.

If you use `cvcp` without any options, it will pull a `rsync` image from Docker Hub, and will use docker with root (`sudo docker`).

The following command line options are available to customise the behaviour:

- `--docker` and `--podman`
  - The container engine to use.
  - The default is `docker`.

- `--rootless`
  - Use the container engine without root (without `sudo`).

- `--image`
  - The container image to be used.
  - Note that the image needs to have `rsync` installed. Read the next section for more details.

- `--rsync-opts`
  - Options to pass to `rsync`.
  - Note that, you need to pass all the options as a quoted string **with a space at the beginning**. For example, `' --verbose'`.
  - Using this option will clear the default `rsync` options used by `cvcp`, so make sure to pass all the options required.
  - The default options are `' -a --progress'`.

- `--no-exec`
  - Print the command and exit.

---

## Using a custom image

To use a custom image with `cvcp`, use the `--image` argument.

To permanently change the default image that `cvcp` uses, change this line in the `cvcp` script file:

```python
RSYNC_IMAGE = "image_name"
```

It is necessary for your custom image to have `rsync` installed. You can use the Dockerfile inside the same repository as a base to build the image.

```bash
# docker
sudo docker build -t localhost/rsync .

# podman
podman build -t localhost/rsync .
```