/busybox/sh: syntax error: bad substitution with Tekton - shell

Question

I'm trying to pull source code from Github then build and push a docker image to docker hub using Tekton pipeline and Knative on Kubernetes cluster.
I'm following this link for the installation and setup of Tekton:
https://www.ibm.com/cloud/blog/build-a-knative-service-with-tekton-and-apache-openwhisk-nodejs-runtime
task-build.yaml
apiVersion: tekton.dev/v1alpha1
kind: Task
metadata:
name: task-build
spec:
inputs:
resources:
- name: docker-source
type: git
params:
- name: TARGET_IMAGE_NAME
description: name of the image to be tagged and pushed
- name: TARGET_IMAGE_TAG
description: tag the image before pushing
default: "latest"
- name: DOCKERFILE
description: name of the dockerfile
- name: OW_RUNTIME_DEBUG
description: flag to indicate debug mode should be on/off
default: "false"
- name: OW_RUNTIME_PLATFORM
description: flag to indicate the platform, one of ["openwhisk", "knative", ... ]
default: "knative"
- name: OW_ACTION_NAME
description: name of the action
default: "foo"
- name: OW_ACTION_CODE
description: JavaScript source code to be evaluated
default: ""
- name: OW_ACTION_MAIN
description: name of the function in the "__OW_ACTION_CODE" to call as the action handler
default: "main"
- name: OW_ACTION_BINARY
description: flag to indicate zip function, for zip actions, "__OW_ACTION_CODE" must be base64 encoded string
default: "false"
- name: OW_HTTP_METHODS
description: list of HTTP methods, any combination of [GET, POST, PUT, and DELETE], default is [POST]
default: "[POST]"
- name: OW_ACTION_RAW
description: flag to indicate raw HTTP handling, interpret and process an incoming HTTP body directly
default: "false"
outputs:
resources:
- name: builtImage
type: image
steps:
- name: add-ow-env-to-dockerfile
image: "gcr.io/kaniko-project/executor:debug"
command:
- /busybox/sh
args:
- -c
- |
cat <<EOF >> ${inputs.params.DOCKERFILE}
ENV __OW_RUNTIME_DEBUG "${inputs.params.OW_RUNTIME_DEBUG}"
ENV __OW_RUNTIME_PLATFORM "${inputs.params.OW_RUNTIME_PLATFORM}"
ENV __OW_ACTION_NAME "${inputs.params.OW_ACTION_NAME}"
ENV __OW_ACTION_CODE "${inputs.params.OW_ACTION_CODE}"
ENV __OW_ACTION_MAIN "${inputs.params.OW_ACTION_MAIN}"
ENV __OW_ACTION_BINARY "${inputs.params.OW_ACTION_BINARY}"
ENV __OW_HTTP_METHODS "${inputs.params.OW_HTTP_METHODS}"
ENV __OW_ACTION_RAW "${inputs.params.OW_ACTION_RAW}"
EOF
- name: adapt-dockerfile-to-tekton
image: "gcr.io/kaniko-project/executor:debug"
command:
- sed
args:
- -i
- -e
- 's/COPY ./COPY .\/docker-source/g'
- ${inputs.params.DOCKERFILE}
- name: build-openwhisk-nodejs-runtime
image: "gcr.io/kaniko-project/executor:latest"
args: ["--destination=${inputs.params.TARGET_IMAGE_NAME}:${inputs.params.TARGET_IMAGE_TAG}", "--dockerfile=${inputs.params.DOCKERFILE}"]
When trying to build and push the image, am getting error:
conditions:
- lastTransitionTime: "2020-09-24T07:33:11Z"
"step-add-ow-env-to-dockerfile" exited with code 2 (image: "docker-pullable://gcr.io/kaniko-project/executor#sha256:0f27b0674797b56db08010dff799c8926c4e9816454ca56cc7844df228c53485"); for logs run: kubectl -n default logs task-run-helloworld-pod-5bbkx -c step-add-ow-env-to-dockerfile
reason: Failed
status: "False"
type: Succeeded
When checked the logs for error msg, I'm getting:
Error : /busybox/sh: syntax error: bad substitution