Inspecting if the docker image with specified tag exists from docker hub registry

is_docker_image_exists.sh

#!/bin/bash

# INPUT:
#   ENV Variables:
#     DOCKER_USERNAME
#     DOCKER_PASSWORD
#     IMAGE_NAME
#     IMAGE_TAG

# OUTPUT:
#   MESSAGE:
#     "true"                Indicating the images with specified tag exists
#     "false, error: xxxx"  Indicating the images does not existing or retrieving image failed.

# Validating if the required envs already injected to the shell
[ -z ${DOCKER_USERNAME} ] && echo "false, ENV VAR 'DOCKER_USERNAME' does not exists" && exit
[ -z ${DOCKER_PASSWORD} ] && echo "false, ENV VAR 'DOCKER_PASSWORD' does not exists" && exit
[ -z ${IMAGE_NAME} ] && echo "false, ENV VAR 'IMAGE_NAME' does not exists" && exit
[ -z ${IMAGE_TAG} ] && echo "false, ENV VAR 'IMAGE_TAG' does not exists" && exit

data_json='{"username": "'${DOCKER_USERNAME}'", "password": "'${DOCKER_PASSWORD}'"}'
login_url="https://hub.docker.com/v2/users/login/"
image_url="https://hub.docker.com/v2/repositories/${IMAGE_NAME}/tags/${IMAGE_TAG}/"

# Getting and validating the JWT token
token_resp=$(curl -s -X POST -H "Content-Type: application/json" -d "${data_json}" $login_url)
token_key=$(echo $token_resp|awk -F '"' '{print $2}')
token_value=$(echo $token_resp|awk -F '"' '{print $4}')

[ ${token_key} != token ] && echo "false, error: Got the invalid login response ${token_resp}" && exit

# Retrieving and validating the image status
image_resp=$(curl -sI -H "Authentication: JWT $token_value" $image_url)
image_status=$(echo ${image_resp}|grep -c '200 OK'||:)

[ ${image_status} -eq 0 ] && echo "false, error: Image does not exists or getting image failed ${image_resp}" && exit

echo "true"