Added pipe and length docs, fix pipe precedence

pkg/yqlib/operator_pipe_test.go

@@ -0,0 +1,31 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var pipeOperatorScenarios = []expressionScenario{
+	{
+		description: "Simple Pipe",
+		document:    `{a: {b: cat}}`,
+		expression:  `.a | .b`,
+		expected: []string{
+			"D0, P[a b], (!!str)::cat\n",
+		},
+	},
+	{
+		description: "Multiple updates",
+		document:    `{a: cow, b: sheep, c: same}`,
+		expression:  `.a = "cat" | .b = "dog"`,
+		expected: []string{
+			"D0, P[], (doc)::{a: cat, b: dog, c: same}\n",
+		},
+	},
+}
+
+func TestPipeOperatorScenarios(t *testing.T) {
+	for _, tt := range pipeOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Pipe", pipeOperatorScenarios)
+}