/bin/sh: =: not found when running docker container from custom image

Question

I try to run a container from a built image and get an error /bin/sh: =:. Is there anyone know how to fix it. Below is my Dockerfile. Both the index.js and package.json are in the same folder with the Dockerfile.

package.json

{
  "dependencies":{
    "express":"*"
  },
  "scripts":{
    "start":"node index.js"
  }
}

Dockerfile

FROM node:14.4.0-alpine3.10
COPY ./ ./
RUN npm install
CMD = ['npm', 'start']

Answer 1

The input to CMD is parsed as a JSON array, which means you have to use double quotes and not single quotes. Additionally, get rid of the =

CMD ["npm", "start"]