Support simple syntax for accessing json. Add tests

docs/expressions.md

@@ -118,10 +118,12 @@ Good for tabulate output separation.
 
 ## Json
 
-Syntax: `{json field expression}`
+Syntax: `{json field expression}` or `{json expression}`
 
 Extract a JSON value based on the expression statement from [gjson](https://github.com/tidwall/gjson)
 
+When only 1 argument is present, it will assume the JSON is in `{0}` (Full match)
+
 See: [json](json.md) for more information.
 
 ## Time

pkg/expressions/funcsJson.go

@@ -5,12 +5,19 @@ import (
 )
 
 func kfJson(args []KeyBuilderStage) KeyBuilderStage {
-	if len(args) != 2 {
-		return stageError(ErrorArgCount)
+	if len(args) == 1 {
+		return KeyBuilderStage(func(context KeyBuilderContext) string {
+			json := context.GetMatch(0)
+			expression := args[0](context)
+			return gjson.Get(json, expression).String()
+		})
+	} else if len(args) == 2 {
+		return KeyBuilderStage(func(context KeyBuilderContext) string {
+			json := args[0](context)
+			expression := args[1](context)
+			return gjson.Get(json, expression).String()
+		})
+	} else {
+		return stageLiteral(ErrorArgCount)
 	}
-	return KeyBuilderStage(func(context KeyBuilderContext) string {
-		json := args[0](context)
-		expression := args[1](context)
-		return gjson.Get(json, expression).String()
-	})
 }

pkg/expressions/funcs_test.go

@@ -102,6 +102,14 @@ func TestJson(t *testing.T) {
 	testExpression(t, mockContext(`{"abc":123}`), `{json {0} abc}`, "123")
 }
 
+func TestJsonSingleArg(t *testing.T) {
+	testExpression(t, mockContext(`{"abc":456}`), `{json abc}`, "456")
+}
+
+func TestJsonManyArgs(t *testing.T) {
+	testExpression(t, mockContext(`{"abc":456}`), `{json {0} abc woops}`, "<ARGN>")
+}
+
 func TestFormat(t *testing.T) {
 	testExpression(t, mockContext(), `{format "%10s" abc}`, "       abc")
 }