Added string trim operator

pkg/yqlib/doc/operators/string-operators.md

@@ -112,6 +112,26 @@ will output
 cat; meow; 1; ; true
 ```
 
+## Trim strings
+Given a sample.yml file of:
+```yaml
+- ' cat'
+- 'dog '
+- ' cow cow '
+- horse
+```
+then
+```bash
+yq '.[] | trim' sample.yml
+```
+will output
+```yaml
+cat
+dog
+cow cow
+horse
+```
+
 ## Match string
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/lexer_participle.go

@@ -152,6 +152,7 @@ var participleYqRules = []*participleYqRule{
 
 	{"Uppercase", `upcase|ascii_?upcase`, opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: true}), 0},
 	{"Downcase", `downcase|ascii_?downcase`, opTokenWithPrefs(changeCaseOpType, nil, changeCasePrefs{ToUpperCase: false}), 0},
+	simpleOp("trim", trimOpType),
 
 	{"HexValue", `0[xX][0-9A-Fa-f]+`, hexValue(), 0},
 	{"FloatValueScientific", `-?[1-9](\.\d+)?[Ee][-+]?\d+`, floatValue(), 0},

pkg/yqlib/lib.go

@@ -146,6 +146,7 @@ var captureOpType = &operationType{Type: "CAPTURE", NumArgs: 1, Precedence: 50,
 var testOpType = &operationType{Type: "TEST", NumArgs: 1, Precedence: 50, Handler: testOperator}
 var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50, Handler: splitStringOperator}
 var changeCaseOpType = &operationType{Type: "CHANGE_CASE", NumArgs: 0, Precedence: 50, Handler: changeCaseOperator}
+var trimOpType = &operationType{Type: "TRIM", NumArgs: 0, Precedence: 50, Handler: trimSpaceOperator}
 
 var loadOpType = &operationType{Type: "LOAD", NumArgs: 1, Precedence: 50, Handler: loadYamlOperator}
 

pkg/yqlib/operator_strings.go

@@ -13,6 +13,26 @@ type changeCasePrefs struct {
 	ToUpperCase bool
 }
 
+func trimSpaceOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	results := list.New()
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		node := unwrapDoc(candidate.Node)
+
+		if guessTagFromCustomType(node) != "!!str" {
+			return Context{}, fmt.Errorf("cannot trim %v, can only operate on strings. ", node.Tag)
+		}
+
+		newStringNode := &yaml.Node{Kind: yaml.ScalarNode, Tag: node.Tag, Style: node.Style}
+		newStringNode.Value = strings.TrimSpace(node.Value)
+		results.PushBack(candidate.CreateReplacement(newStringNode))
+
+	}
+
+	return context.ChildContext(results), nil
+}
+
 func changeCaseOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	results := list.New()
 	prefs := expressionNode.Operation.Preferences.(changeCasePrefs)

pkg/yqlib/operator_strings_test.go

@@ -47,6 +47,17 @@ var stringsOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!str)::cat; meow; 1; ; true\n",
 		},
 	},
+	{
+		description: "Trim strings",
+		document:    `[" cat", "dog ", " cow cow ", horse]`,
+		expression:  `.[] | trim`,
+		expected: []string{
+			"D0, P[0], (!!str)::cat\n",
+			"D0, P[1], (!!str)::dog\n",
+			"D0, P[2], (!!str)::cow cow\n",
+			"D0, P[3], (!!str)::horse\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   `[!horse cat, !goat meow, !frog 1, null, true]`,