Running a bash script from alpine based docker

To run a bash script in alpine based image, you need to do either one

1. Install bash

   $ RUN apk add --update bash
   

2. Use #!/bin/sh in script instead of #!/bin/bash

You need to do any one of these two or both

Or, like @Maroun's answer in comment, you can change your CMD to execute your bash script

CMD ["sh", "./script.sh"]