Add some command line flags

README.md

@@ -4,4 +4,12 @@ Checks current running containers for newer tags according to semver
 
 Usage:
 
-     go run .
+    go run . -h
+
+      -max-pages int
+           max number of pages to retrieve from registry (default 10)
+      -registry-url string
+           base url of the registry you want to check against (default "https://registry.hub.docker.com")
+      -version
+           display the version of dockron and exit
+

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"flag"
 	"fmt"
 	"net/http"
 	"os"
@@ -15,12 +16,17 @@ import (
 	dockerClient "github.com/docker/docker/client"
 )
 
-// Default values for fetching tags from registry
-var registryBase = "https://registry.hub.docker.com"
-var maxPages = 10
+var (
+	// registryBaseURL is the base URL of the docker registry
+	registryBaseURL = "https://registry.hub.docker.com"
+	// maxPages is the max number of pages to fetch from docker registry results
+	maxPages = 10
 
-// Regexp used to extract tag information
-var tagRegexp = regexp.MustCompile(`(.*):[vV]{0,1}([0-9.]+)(-(.*)){0,1}`)
+	// Regexp used to extract tag information
+	tagRegexp = regexp.MustCompile(`(.*):[vV]{0,1}([0-9.]+)(-(.*)){0,1}`)
+	// version of tag checker
+	version = "dev"
+)
 
 // ImageTag is wraps an image and tag values for a container
 type ImageTag struct {
@@ -126,7 +132,7 @@ func listTags(current ImageTag) ([]ImageTag, error) {
 		}
 	}
 
-	url := fmt.Sprintf("%s/v2/repositories/%s/tags", registryBase, current.Image)
+	url := fmt.Sprintf("%s/v2/repositories/%s/tags", registryBaseURL, current.Image)
 	pageCount := 0
 	var response tagsResponse
 	var newTag ImageTag
@@ -166,6 +172,16 @@ func getNewerTags(current ImageTag) ([]ImageTag, error) {
 }
 
 func main() {
+	flag.StringVar(&registryBaseURL, "registry-url", registryBaseURL, "base url of the registry you want to check against")
+	flag.IntVar(&maxPages, "max-pages", maxPages, "max number of pages to retrieve from registry")
+	var showVersion = flag.Bool("version", false, "display the version and exit")
+	flag.Parse()
+
+	// Print version if asked
+	if *showVersion {
+		fmt.Println("version:", version)
+		os.Exit(0)
+	}
 	dockerClient, err := dockerClient.NewClientWithOpts(dockerClient.FromEnv)
 	if err != nil {
 		fmt.Println("Could not initialize docker client")