How can I split string in ARG in Dockerfile to form new ENVs?

ARG MYVAR
ENV credentials ${MYVAR//\// }
ENV USER ${credentials[0]}
ENV PASSWORD ${credentials[1]}
CMD echo USER: $USER PASSWORD: $PASSWORD

When I build, I run into error:

Step 4/7 : ENV credentials ${MYVAR//\// }
 ---> Using cache
 ---> 5c56d29448de
Step 5/7 : ENV USER ${credentials[0]}
failed to process "${credentials[0]}": unsupported modifier ([) in substitution

How can I split string in ARG in Dockerfile to form new ENVs?

ARG MYVAR
ENV credentials ${MYVAR//\// }
ENV USER ${credentials[0]}
ENV PASSWORD ${credentials[1]}
CMD echo USER: $USER PASSWORD: $PASSWORD

When I build, I run into error:

Step 4/7 : ENV credentials ${MYVAR//\// }
 ---> Using cache
 ---> 5c56d29448de
Step 5/7 : ENV USER ${credentials[0]}
failed to process "${credentials[0]}": unsupported modifier ([) in substitution

• bash
• split
• dockerfile
• environment-variables

• 1 Isn't using additional shell script in your Dockerfile an option to split strings? – 3aska Commented Mar 26 at 14:03

1 Answer 1

ARG CREDENTIALS
ARG user="${CREDENTIALS%/*}"
ARG password="${CREDENTIALS#*/}"
ENV USER $user
ENV PASSWORD $password