Shell script to download docker images

docker-whiten.sh

#!/bin/bash

set -xe

# Prints usage message
BASENAME="$0"
usage ()
{
    echo "Usage : (basename "$BASENAME") [options]"
    echo ""
    echo "Description: Downloads artifacts from maven central repository with sources and javadocs"
    echo ""
    echo "Options:"
    echo "-d,--dest <arg>        Destination for downloaded images. Should be without "
    echo "                       a trailing slash and must exist, defaults to 'whiten'"
    echo "-i,--image <arg>       Image's identifier"
    echo "-f,--file <arg>        Get image identifiers list from file"
    echo "-h,--help              Display help information"
}

download_image()
{
    docker pull $2
    # Remvoe invalid characters from image name
    filtered_file_name=$(echo $2 |  sed 's/[^A-Za-z0-9.]/-/g')
    docker save -o "${1}/${filtered_file_name}.tar" $2
}

# Get arguments
DEST='whiten'
while [ "$1" != "" ]; do
    case $1 in
        -i | --image ) shift
                          IMAGE=$1
                          ;;
        -f | --file )     shift
                          FILE=$1
                          ;;
        -d | --dest )     shift
                          DEST=$1
                          ;;
        -h | --help )     usage
                          exit
                          ;;
        * )               usage
                          exit 1
    esac
    shift
done

# Validate arguments
if [ "$DEST" = "" ]; then
    usage
    exit 1
fi
if [ "$IMAGE" = "" ]; then
    if [ "$FILE" = "" ]; then
        usage
        exit 1
    else
        while read -r line || [[ -n "$line" ]]; do
            download_image $DEST $line
        done < "$FILE"
    fi
else
    download_image $DEST $IMAGE
fi