Podman equivalent to Docker Compose environment variable substitution

In your example, you can use bash shell expansion:

IMAGE_TAG="v0.0.0"
printf "
version: '2.2'
services:
  example-service:
    image: busybox:${IMAGE_TAG:-latest}
    scale: ${REPLICAS:-1}
    command: ls
"

Yields:

version: '2.2'
services:
  example-service:
    image: busybox:v0.0.0
    scale: 1
    command: ls

kubectl (!) supports piping stdin directly (and podman may too), so you can in theory (though it's nearly always better to persist the output to a file so that you can commit a record of what you apply):

IMAGE_TAG="v0.0.0"
printf "
version: '2.2'
services:
  example-service:
    image: busybox:${IMAGE_TAG:-latest}
    scale: ${REPLICAS:-1}
    command: ls
" \
| kubectl apply --filename=-

I have begun using yq to template my YAML files but previous simply used sed. Using the former, you can use a YAML query syntax to path to values that you want to replace and, with sed, of course, regular expressions.

Helm and other (Kubernetes) tools use Go templating to solve a similar problem and it remains something of an outstanding issue (unless you're happy to adopt *nix's philosophy of having tools that do one thing well)

Podman equivalent to Docker Compose environment variable substitution

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