Added eval operator

pkg/yqlib/operator_eval_test.go

@@ -0,0 +1,34 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var evalOperatorScenarios = []expressionScenario{
+
+	{
+		description: "Dynamically evaluate a path",
+		document:    `{pathExp: '.a.b[] | select(.name == "cat")', a: {b: [{name: dog}, {name: cat}]}}`,
+		expression:  `eval(.pathExp)`,
+		expected: []string{
+			"D0, P[a b 1], (!!map)::{name: cat}\n",
+		},
+	},
+	{
+		description:         "Dynamically update a path from an environment variable",
+		subdescription:      "The env variable can be any valid yq expression.",
+		document:            `{a: {b: [{name: dog}, {name: cat}]}}`,
+		environmentVariable: ".a.b[0].name",
+		expression:          `eval(strenv(myenv)) = "cow"`,
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: [{name: cow}, {name: cat}]}}\n",
+		},
+	},
+}
+
+func TestEvalOperatorsScenarios(t *testing.T) {
+	for _, tt := range evalOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentOperatorScenarios(t, "eval", evalOperatorScenarios)
+}