Merged envsubst into env operators

pkg/yqlib/operator_env.go

@@ -1,10 +1,12 @@
 package yqlib
 
 import (
+	"container/list"
 	"fmt"
 	"os"
 	"strings"
 
+	envsubst "github.com/a8m/envsubst"
 	yaml "gopkg.in/yaml.v3"
 )
 
@@ -47,3 +49,26 @@ func envOperator(d *dataTreeNavigator, context Context, expressionNode *Expressi
 
 	return context.SingleChildContext(target), nil
 }
+
+func envsubstOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		if node.Tag != "!!str" {
+			log.Warning("EnvSubstOperator, env name:", node.Tag, node.Value)
+			return Context{}, fmt.Errorf("cannot substitute with %v, can only substitute strings. Hint: Most often you'll want to use '|=' over '=' for this operation", node.Tag)
+		}
+
+		value, err := envsubst.String(node.Value)
+		if err != nil {
+			return Context{}, err
+		}
+		targetNode := &yaml.Node{Kind: yaml.ScalarNode, Value: value, Tag: "!!str"}
+		result := candidate.CreateReplacement(targetNode)
+		results.PushBack(result)
+	}
+
+	return context.ChildContext(results), nil
+}