added option to pass desired version via command line

main.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"regexp"
 
 	"github.com/manifoldco/promptui"
 	"github.com/pborman/getopt"
@@ -33,35 +34,69 @@ var version = "0.1.0\n"
 
 func main() {
 
+	versionFlag := getopt.BoolLong("version", 'v', "displays the version of tgshift")
+	helpFlag := getopt.BoolLong("help", 'h', "displays help message")
+	_ = versionFlag
+
 	getopt.Parse()
 	args := getopt.Args()
 
-	if len(args) == 0 {
-
-		tglist, _ := lib.GetTGList(terragruntURL)
-		recentVersions, _ := lib.GetRecentVersions() //get recent versions from RECENT file
-		tglist = append(recentVersions, tglist...)   //append recent versions to the top of the list
-		tglist = lib.RemoveDuplicateVersions(tglist) //remove duplicate version
-
-		/* prompt user to select version of terragrunt */
-		prompt := promptui.Select{
-			Label: "Select terragrunt version",
-			Items: tglist,
-		}
-
-		_, tgversion, errPrompt := prompt.Run()
+	if *versionFlag {
+		fmt.Printf("\nVersion: %v\n", version)
+	} else if *helpFlag {
+		usageMessage()
+	} else {
 
-		if errPrompt != nil {
-			log.Printf("Prompt failed %v\n", errPrompt)
-			os.Exit(1)
+		if len(args) == 1 {
+
+			semverRegex := regexp.MustCompile(`\A\d+(\.\d+){2}\z`)
+			if semverRegex.MatchString(args[0]) {
+				requestedVersion := args[0]
+
+				//check if version exist before downloading it
+				tflist, _ := lib.GetTGList(terragruntURL)
+				exist := lib.VersionExist(requestedVersion, tflist)
+
+				if exist {
+					lib.AddRecent(requestedVersion) //add to recent file for faster lookup
+					lib.Install(requestedVersion)
+				} else {
+					fmt.Println("Not a valid terragrunt version")
+				}
+
+			} else {
+				fmt.Println("Not a valid terragrunt version")
+				fmt.Println("Args must be a valid terragrunt version")
+				usageMessage()
+			}
+
+		} else if len(args) == 0 {
+
+			tglist, _ := lib.GetTGList(terragruntURL)
+			recentVersions, _ := lib.GetRecentVersions() //get recent versions from RECENT file
+			tglist = append(recentVersions, tglist...)   //append recent versions to the top of the list
+			tglist = lib.RemoveDuplicateVersions(tglist) //remove duplicate version
+
+			/* prompt user to select version of terragrunt */
+			prompt := promptui.Select{
+				Label: "Select terragrunt version",
+				Items: tglist,
+			}
+
+			_, tgversion, errPrompt := prompt.Run()
+
+			if errPrompt != nil {
+				log.Printf("Prompt failed %v\n", errPrompt)
+				os.Exit(1)
+			}
+
+			fmt.Printf("Terragrunt version %q selected\n", tgversion)
+			lib.Install(tgversion)
+			lib.AddRecent(tgversion) //add to recent file for faster lookup (cache)
+			os.Exit(0)
+		} else {
+			usageMessage()
 		}
-
-		fmt.Printf("Terragrunt version %q selected\n", tgversion)
-		lib.Install(tgversion)
-		lib.AddRecent(tgversion) //add to recent file for faster lookup (cache)
-		os.Exit(0)
-	} else {
-		usageMessage()
 	}
 
 }