Add version cli argument

Author: aerialls

README.md

@@ -93,6 +93,8 @@ Usage of ./nginx-prometheus-exporter:
         An address or unix domain socket path to listen on for web interface and telemetry. The default value can be overwritten by LISTEN_ADDRESS environment variable. (default ":9113")
   -web.telemetry-path string
         A path under which to expose metrics. The default value can be overwritten by TELEMETRY_PATH environment variable. (default "/metrics")
+  -version
+        Display the NGINX exporter version. (default false)
 ```
 
 ### Exported Metrics

exporter.go

@@ -264,6 +264,9 @@ For NGINX, the stub_status page must be available through the URI. For NGINX Plu
 	nginxRetries = flag.Uint("nginx.retries",
 		defaultNginxRetries,
 		"A number of retries the exporter will make on start to connect to the NGINX stub_status page/NGINX Plus API before exiting with an error. The default value can be overwritten by NGINX_RETRIES environment variable.")
+	displayVersion = flag.Bool("version",
+		false,
+		"Display the NGINX exporter version.")
 
 	// Custom command-line flags
 	timeout = createPositiveDurationFlag("nginx.timeout",
@@ -282,6 +285,11 @@ For NGINX, the stub_status page must be available through the URI. For NGINX Plu
 func main() {
 	flag.Parse()
 
+	if *displayVersion {
+		fmt.Printf("NGINX Prometheus Exporter Version=%v GitCommit=%v\n", version, gitCommit)
+		os.Exit(0)
+	}
+
 	log.Printf("Starting NGINX Prometheus Exporter Version=%v GitCommit=%v", version, gitCommit)
 
 	registry := prometheus.NewRegistry()