How to Merge Docker Compose file with Bash - bash

Question

I'm trying to merge the docker-compose.yml file with the docker-compose2.yml file with bash.
docker-compose.yml :
version: "3"
services:
nexus:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8081:8081"
volumes:
nexus-data: {}
docker-compose2.yml :
version: "3"
services:
nexus2:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8082:8082"
volumes:
nexus-data: {}
Output I Want:
version: "3"
services:
nexus:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8081:8081"
nexus2:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8082:8082"
volumes:
nexus-data: {}
How do I get this output with bash?

Answer 1

The Docker Compose config command does exactly what you need, it takes multiple compose file and merges them.
Just pass them using multiple -f flags:
docker-compose -f docker-compose.yml -f docker-compose2.yml config
or using an environment variable:
COMPOSE_FILE=docker-compose.yml:docker-compose2.yml docker-compose config
The same approach is valid for every Docker Compose command, so if your final target is, for example, to set up your project, you can directly run:
docker-compose -f docker-compose.yml -f docker-compose2.yml up
Check the documentation for further details on how to specify multiple compose files.

Answer 2

I don't think you can do this (easily as a one-liner) in native bash without writing a script. I was curious so I did a quick search and found a yaml manipulation tool which supports merging yaml (docker-compose) files and looks like it fits your use-case.
I used brew to install on MacOS but there are instructions for Linux as well - https://mikefarah.github.io/yq/.
brew install yq
Showing existing files:
$ cat file1.yaml
version: "3"
services:
nexus:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8081:8081"
volumes:
nexus-data: {}
$ cat file2.yaml
version: "3"
services:
nexus2:
image: sonatype/nexus3
volumes:
- "/opt/nexus3/nexus-data:/nexus-data"
ports:
- "8082:8082"
volumes:
nexus-data: {}
Merge both files outputting to stdout:
$ yq m file1.yaml file2.yaml
services:
nexus:
image: sonatype/nexus3
ports:
- 8081:8081
volumes:
- /opt/nexus3/nexus-data:/nexus-data
nexus2:
image: sonatype/nexus3
ports:
- 8082:8082
volumes:
- /opt/nexus3/nexus-data:/nexus-data
version: "3"
volumes:
nexus-data: {}
There may be a native way but I just redirected the stdout to a file:
$ yq m file1.yaml file2.yaml > file3.yaml
$ cat file3.yaml
services:
nexus:
image: sonatype/nexus3
ports:
- 8081:8081
volumes:
- /opt/nexus3/nexus-data:/nexus-data
nexus2:
image: sonatype/nexus3
ports:
- 8082:8082
volumes:
- /opt/nexus3/nexus-data:/nexus-data
version: "3"
volumes:
nexus-data: {}
There are a lot of examples in their documentation for you to explore - https://mikefarah.github.io/yq/merge/.