Added join strings operator

pkg/yqlib/doc/String Operators.md

@@ -0,0 +1,19 @@
+
+## Join strings
+Given a sample.yml file of:
+```yaml
+- cat
+- meow
+- 1
+- null
+- true
+```
+then
+```bash
+yq eval 'join("; ")' sample.yml
+```
+will output
+```yaml
+cat; meow; 1; ; true
+```
+

pkg/yqlib/expression_tokeniser.go

@@ -243,6 +243,8 @@ func initLexer() (*lex.Lexer, error) {
 	lexer.Add([]byte(`di`), opToken(getDocumentIndexOpType))
 	lexer.Add([]byte(`splitDoc`), opToken(splitDocumentOpType))
 
+	lexer.Add([]byte(`join`), opToken(joinStringOpType))
+
 	lexer.Add([]byte(`style`), opAssignableToken(getStyleOpType, assignStyleOpType))
 
 	lexer.Add([]byte(`tag`), opAssignableToken(getTagOpType, assignTagOpType))

pkg/yqlib/lib.go

@@ -64,6 +64,7 @@ var getPathOpType = &operationType{Type: "GET_PATH", NumArgs: 0, Precedence: 50,
 
 var explodeOpType = &operationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50, Handler: explodeOperator}
 var sortKeysOpType = &operationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: sortKeysOperator}
+var joinStringOpType = &operationType{Type: "JOIN", NumArgs: 1, Precedence: 50, Handler: joinStringOperator}
 
 var collectObjectOpType = &operationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: collectObjectOperator}
 var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 50, Handler: traversePathOperator}

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"}
+}

pkg/yqlib/operator_strings_test.go

@@ -0,0 +1,23 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var stringsOperatorScenarios = []expressionScenario{
+	{
+		description: "Join strings",
+		document:    `[cat, meow, 1, null, true]`,
+		expression:  `join("; ")`,
+		expected: []string{
+			"D0, P[], (!!str)::cat; meow; 1; ; true\n",
+		},
+	},
+}
+
+func TestStringsOperatorScenarios(t *testing.T) {
+	for _, tt := range stringsOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "String Operators", stringsOperatorScenarios)
+}