Backup a single volume from a container to a tar archive

volume_backup.sh

#!/bin/bash
# Backup a single volume from a Docker container to a tar archive.

CONTAINER_NAME=$1
VOLUME_NAME=$2
BACKUPTAR=$3

usage() {
  echo "Usage: $0 [container name] [volume name] ([backup.tar])"
  exit 1
}

if [ -z $BACKUPTAR ]
then
  BACKUPTAR="backup.tar"
fi

TARDIR=$(dirname "${BACKUPTAR}")
TARFN=$(basename "${BACKUPTAR}")

if [[ $TARDIR != /* ]]
then
  TARDIR="$(pwd)/$TARDIR"
fi

if [ -z $CONTAINER_NAME ]
then
  echo "Error: missing container name parameter."
  usage
fi

if [ -z $VOLUME_NAME ]
then
  echo "Error: missing volume name parameter."
  usage
fi

docker run --rm --volumes-from $CONTAINER_NAME -v $TARDIR:/backup busybox tar cvf /backup/$TARFN $VOLUME_NAME