Fixed create yaml

cmd/evalute_sequence_command.go

@@ -63,7 +63,6 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 	printer := yqlib.NewPrinter(out, outputToJSON, unwrapScalar, colorsEnabled, indent, !noDocSeparators)
 
 	streamEvaluator := yqlib.NewStreamEvaluator()
-	allAtOnceEvaluator := yqlib.NewAllAtOnceEvaluator()
 
 	switch len(args) {
 	case 0:
@@ -75,7 +74,7 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 		}
 	case 1:
 		if nullInput {
-			err = allAtOnceEvaluator.EvaluateFiles(args[0], []string{}, printer)
+			err = streamEvaluator.EvaluateNew(args[0], printer)
 		} else {
 			err = streamEvaluator.EvaluateFiles("", []string{args[0]}, printer)
 		}

pkg/yqlib/doc/Assign.md

@@ -5,6 +5,18 @@ Which will assign the LHS node values to the RHS node values. The RHS expression
 
 ### relative form: `|=`
 This will do a similar thing to the plain form, however, the RHS expression is run against _the LHS nodes_. This is useful for updating values based on old values, e.g. increment.
+## Create yaml file
+Running
+```bash
+yq eval --null-input '(.a.b = "cat") | (.x = "frog")'
+```
+will output
+```yaml
+a:
+  b: cat
+x: frog
+```
+
 ## Update node to be the child value
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/operator_assign.go

@@ -36,6 +36,11 @@ func AssignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNo
 			candidate.UpdateFrom(first.Value.(*CandidateNode))
 		}
 	}
+	// // if there was nothing given, perhaps we are creating a new yaml doc
+	// if matchingNodes.Len() == 0 {
+	// 	log.Debug("started with nothing, returning LHS, %v", lhs.Len())
+	// 	return lhs, nil
+	// }
 	return matchingNodes, nil
 }
 

pkg/yqlib/operator_assign_test.go

@@ -5,6 +5,13 @@ import (
 )
 
 var assignOperatorScenarios = []expressionScenario{
+	{
+		description: "Create yaml file",
+		expression:  `(.a.b = "cat") | (.x = "frog")`,
+		expected: []string{
+			"D0, P[], ()::a:\n    b: cat\nx: frog\n",
+		},
+	},
 	{
 		description: "Update node to be the child value",
 		document:    `{a: {b: {g: foof}}}`,

pkg/yqlib/operators_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"github.com/mikefarah/yq/v4/test"
+	yaml "gopkg.in/yaml.v3"
 )
 
 type expressionScenario struct {
@@ -40,6 +41,15 @@ func testScenario(t *testing.T, s *expressionScenario) {
 			t.Error(err, s.document)
 			return
 		}
+	} else {
+		candidateNode := &CandidateNode{
+			Document:  0,
+			Filename:  "",
+			Node:      &yaml.Node{Tag: "!!null"},
+			FileIndex: 0,
+		}
+		inputs.PushBack(candidateNode)
+
 	}
 
 	results, err = treeNavigator.GetMatchingNodes(inputs, node)
@@ -152,20 +162,20 @@ func documentScenarios(t *testing.T, title string, scenarios []expressionScenari
 			var output bytes.Buffer
 			var err error
 			printer := NewPrinter(bufio.NewWriter(&output), false, true, false, 2, true)
+			streamEvaluator := NewStreamEvaluator()
 
 			if s.document != "" {
 				node, err := treeCreator.ParsePath(s.expression)
 				if err != nil {
 					t.Error(err)
 				}
-				streamEvaluator := NewStreamEvaluator()
 				err = streamEvaluator.Evaluate("sample.yaml", strings.NewReader(formattedDoc), node, printer)
+
 				if err != nil {
 					t.Error(err)
 				}
 			} else {
-				allAtOnceEvaluator := NewAllAtOnceEvaluator()
+				err = streamEvaluator.EvaluateNew(s.expression, printer)
-				err = allAtOnceEvaluator.EvaluateFiles(s.expression, []string{}, printer)
 				if err != nil {
 					t.Error(err)
 				}

pkg/yqlib/stream_evaluator.go

@@ -11,6 +11,7 @@ import (
 type StreamEvaluator interface {
 	Evaluate(filename string, reader io.Reader, node *PathTreeNode, printer Printer) error
 	EvaluateFiles(expression string, filenames []string, printer Printer) error
+	EvaluateNew(expression string, printer Printer) error
 }
 
 type streamEvaluator struct {
@@ -23,6 +24,27 @@ func NewStreamEvaluator() StreamEvaluator {
 	return &streamEvaluator{treeNavigator: NewDataTreeNavigator(), treeCreator: NewPathTreeCreator()}
 }
 
+func (s *streamEvaluator) EvaluateNew(expression string, printer Printer) error {
+	node, err := treeCreator.ParsePath(expression)
+	if err != nil {
+		return err
+	}
+	candidateNode := &CandidateNode{
+		Document:  0,
+		Filename:  "",
+		Node:      &yaml.Node{Tag: "!!null"},
+		FileIndex: 0,
+	}
+	inputList := list.New()
+	inputList.PushBack(candidateNode)
+
+	matches, errorParsing := treeNavigator.GetMatchingNodes(inputList, node)
+	if errorParsing != nil {
+		return errorParsing
+	}
+	return printer.PrintResults(matches)
+}
+
 func (s *streamEvaluator) EvaluateFiles(expression string, filenames []string, printer Printer) error {
 
 	node, err := treeCreator.ParsePath(expression)