Compare two different docker images a and b

compare.sh

#!/bin/bash
IMAGE_A=$1
IMAGE_B=$2
TMP_DIR=$(mktemp -d)

cleanup() {
  rm -rf "$TMP_DIR"
}

# Trap signals
# SIGINT is the signal sent to a process by its controlling terminal when a user wishes to interrupt the process.
# SIGTERM is a signal sent to a process to request its termination.
# EXIT is a pseudo-signal used to trap script exit.
trap cleanup SIGINT SIGTERM EXIT

cd $TMP_DIR
mkdir a; pushd a; (docker save $IMAGE_A | tar xvf -); popd
mkdir b; pushd b; (docker save $IMAGE_B | tar xvf -); popd
LAYERS=$(cat a/manifest.json| jq -r ".[0].Layers|length")
for LAYER in $(seq 1 $LAYERS); do
    SHA_A=$(cat a/manifest.json| jq -r ".[0].Layers[$LAYER-1]")
    SHA_B=$(cat b/manifest.json| jq -r ".[0].Layers[$LAYER-1]")
    if [ "$SHA_A" != "$SHA_B" ]; then
        echo "Difference found in layer $LAYER"
        cmp a/$SHA_A b/$SHA_B || pkgdiff a/$SHA_A b/$SHA_B
        exit 1
    fi
done