Get all steps used during container image building (aka Dockerfile instructions)

simple_image_walk.sh

#!/bin/bash

IMAGE=$1
PARENT=$IMAGE

declare -a RESULTS REV_RESULTS

while [ -n "${PARENT}" ]; do
    JSON=$(docker inspect $PARENT |jq .)
    RESULTS+=("$(echo $JSON | jq '.[0]'.ContainerConfig.Cmd)")
    PARENT=$(echo $JSON | jq '.[0]'.Parent |tr -d '\"')

    echo $PARENT | grep -q ':' > /dev/null 2>&1
    if [ $? -eq 0 ]; then
        PARENT=$(echo $PARENT | cut -d':' -f2)
    fi
done

for (( i=${#RESULTS[@]}-1; i>=0; i-- )); do
    REV_RESULTS[${#REV_RESULTS[@]}]=${RESULTS[i]}
done

for cmd in "${REV_RESULTS[@]}"; do
    echo $cmd
done