Added join strings operator

pkg/yqlib/operator_strings.go

@@ -0,0 +1,50 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+func joinStringOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+	log.Debugf("-- joinStringOperator")
+	joinStr := ""
+
+	rhs, err := d.GetMatchingNodes(matchMap, expressionNode.Rhs)
+	if err != nil {
+		return nil, err
+	}
+	if rhs.Front() != nil {
+		joinStr = rhs.Front().Value.(*CandidateNode).Node.Value
+	}
+
+	var results = list.New()
+
+	for el := matchMap.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		if node.Kind != yaml.SequenceNode {
+			return nil, fmt.Errorf("Cannot join with %v, can only join arrays of scalars", node.Tag)
+		}
+		targetNode := join(node.Content, joinStr)
+		result := candidate.CreateChild(nil, targetNode)
+		results.PushBack(result)
+	}
+
+	return results, nil
+}
+
+func join(content []*yaml.Node, joinStr string) *yaml.Node {
+	var stringsToJoin []string
+	for _, node := range content {
+		str := node.Value
+		if node.Tag == "!!null" {
+			str = ""
+		}
+		stringsToJoin = append(stringsToJoin, str)
+	}
+
+	return &yaml.Node{Kind: yaml.ScalarNode, Value: strings.Join(stringsToJoin, joinStr), Tag: "!!str"}
+}