run,create: add support for --env-merge for preprocessing vars

Allow end users to preprocess default environment variables before
injecting them into container using `--env-merge`

Usage
```
podman run -it --rm --env-merge some=${some}-edit --env-merge
some2=${some2}-edit2 myimage sh
```

Closes: https://github.com/containers/podman/issues/15288

Signed-off-by: Aditya R <arajan@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/pkg/specgen/generate/container.go b/pkg/specgen/generate/container.go
index 85cd8f5ca..e293ce010 100644
--- a/pkg/specgen/generate/container.go
+++ b/pkg/specgen/generate/container.go
@@ -19,6 +19,7 @@ import (
 	"github.com/containers/podman/v4/pkg/signal"
 	"github.com/containers/podman/v4/pkg/specgen"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/openshift/imagebuilder"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
@@ -131,6 +132,17 @@ func CompleteSpec(ctx context.Context, r *libpod.Runtime, s *specgen.SpecGenerat
 		defaultEnvs = envLib.Join(envLib.DefaultEnvVariables(), envLib.Join(defaultEnvs, envs))
 	}
 
+	for _, e := range s.EnvMerge {
+		processedWord, err := imagebuilder.ProcessWord(e, envLib.Slice(defaultEnvs))
+		if err != nil {
+			return nil, fmt.Errorf("unable to process variables for --env-merge %s: %w", e, err)
+		}
+		splitWord := strings.Split(processedWord, "=")
+		if _, ok := defaultEnvs[splitWord[0]]; ok {
+			defaultEnvs[splitWord[0]] = splitWord[1]
+		}
+	}
+
 	for _, e := range s.UnsetEnv {
 		delete(defaultEnvs, e)
 	}