bash script to flatten docker images down to one layer of files

docker_flatten.sh

#!/bin/bash
# by: Marcin Pohl
# created: 2021-06-30
# this bash script js used to flatten and optimize
#   docker images for better file access times.
​
function docker_flatten() {
    [[ $# -ne 2 ]] && ( echo "Example usage: docker_flatten python:3.7-slim python:3.7-slim-flat"; exit 255 )
​
    local SRC="$1"  # Name or SHA of the source image
    local TGT="$2"  # Name and optional tag of the target image
​
    ID=$(docker run -d "$SRC" /bin/bash)
    ### the actual flattening is export + import
    docker export "$ID" | docker import - "$TGT"
    docker container stop "$ID"
​
    SRC_SIZE=$(docker inspect --format '{{.Size}}' "$SRC")
    TGT_SIZE=$(docker inspect --format '{{.Size}}' "$TGT")
    echo "" \
    | awk -v src="$SRC_SIZE" -v tgt="$TGT_SIZE" \
        '{printf "Flattened image is %3.1f%% of the old one.\n", 100*tgt/src}'
}
​