cmd/ecs - add CLI tool to check if field exists (#20)

cmd/ecs/ecs.go

@@ -0,0 +1,100 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/andrewkroh/go-ecs"
+)
+
+var usage = `ecs [field]
+
+ecs is a command-line tool for retrieving definitions of Elastic Common Schema
+(ECS) fields. The field definition is written as JSON to stdout.
+
+See https://www.elastic.co/guide/en/ecs/current/ecs-field-reference.html
+
+OPTIONS:
+
+  -h           Show this help message and exit.
+  -r           ECS release version (e.g. 8.11.0 or 8.11 or 8).
+               Defaults to latest version incorporated into
+               github.com/andrewkroh/go-ecs at build time.
+  -q           Quiet mode. No ECS definition is written to stdout.
+
+ARGUMENTS:
+
+  field        The name of the ECS field to retrieve the definition for.
+               This argument is required.
+
+EXAMPLES:
+
+  ecs source.ip
+    Retrieves the JSON definition of the "source.ip" ECS field. 
+
+EXIT STATUS:
+
+   0       Successful completion. Field is defined in ECS.
+   1       Field not defined.
+   2       Usage/argument problem.
+`
+
+var (
+	ecsVersion = flag.String("r", "", "ECS release version")
+	quiet      = flag.Bool("q", false, "Quiet mode")
+)
+
+func main() {
+	// Flag handling.
+	flag.Usage = func() {
+		fmt.Fprintln(os.Stderr, usage)
+		os.Exit(2)
+	}
+	flag.Parse()
+
+	if len(flag.Args()) == 0 {
+		flag.Usage()
+	}
+	if len(flag.Args()) > 1 {
+		fmt.Fprintln(os.Stderr, "Only one field name may be specified.")
+		os.Exit(2)
+	}
+
+	// ECS lookup.
+	field, err := ecs.Lookup(flag.Arg(0), *ecsVersion)
+	if err != nil {
+		if !*quiet {
+			fmt.Fprintln(os.Stderr, err)
+		}
+		os.Exit(1)
+	}
+
+	if !*quiet {
+		// Dump as pretty JSON.
+		data, err := json.MarshalIndent(field, "", "  ")
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(2)
+		}
+		fmt.Printf("%s\n", data)
+	}
+}