factor out argument checking into function

comitium.go

@@ -19,11 +19,7 @@ import (
 )
 
 func main() {
-	if len(os.Args) < 2 {
-		fmt.Fprint(os.Stderr, "Please provide a command.\n\n")
-		usage()
-		os.Exit(1)
-	}
+	argCheck(os.Args, 2, true, "Please provide a command.")
 
 	// these are special cases where we shouldn't bother to do anything else
 	if os.Args[1] == "help" {
@@ -59,26 +55,15 @@ func main() {
 
 	switch os.Args[1] {
 	case "refresh":
-		if len(c.Args()) != 0 {
-			fmt.Fprint(os.Stderr, "\"refresh\" doesn't take an argument!\n\n")
-			usage()
-			os.Exit(1)
-		}
+		argCheck(c.Args(), 0, false, "'refresh' doesn't take an argument!")
 		fetch.RefreshAll(&core.Data, *refreshWorkersFlag)
 	case "list":
-		if len(c.Args()) != 0 {
-			fmt.Fprint(os.Stderr, "\"list\" doesn't take an argument!\n\n")
-			usage()
-			os.Exit(1)
-		}
+		argCheck(c.Args(), 0, false, "'list' doesn't take an argument!")
 		// TODO
 		fmt.Fprintln(os.Stderr, "Not Yet Implemented")
 	case "add":
-		if len(c.Args()) < 1 {
-			fmt.Fprint(os.Stderr, "Please provide a URL to add.\n\n")
-			usage()
-			os.Exit(1)
-		}
+		argCheck(c.Args(), 1, true, "Please provide a URL to add.")
+
 		remote, err := url.Parse(c.Arg(0))
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "Error parsing URL: %v\n", err)
@@ -94,11 +79,7 @@ func main() {
 			os.Exit(1)
 		}
 	case "remove":
-		if len(c.Args()) < 1 {
-			fmt.Fprint(os.Stderr, "Please provide a URL to remove.\n\n")
-			usage()
-			os.Exit(1)
-		}
+		argCheck(c.Args(), 1, true, "Please provide a URL to remove.")
 		// TODO
 		fmt.Fprintln(os.Stderr, "Not Yet Implemented")
 	}
@@ -110,6 +91,17 @@ func main() {
 	}
 }
 
+// argCheck makes sure that the target number of arguments are given.  If
+// not, msg is displayed alongside usage information and then the program exits
+// with failure.
+func argCheck(args []string, target int, lt bool, msg string) {
+	if (lt && len(args) < target) || (!lt && len(args) != target) {
+		fmt.Fprint(os.Stderr, msg, "\n\n")
+		usage()
+		os.Exit(1)
+	}
+}
+
 // verifyPath will expand ~ if neccessary and will clean the path.
 func verifyPath(p string) string {
 	if n, err := homedir.Expand(p); err != nil {