Print error if input file is a directory; print program name before error string

cmd/main.go

@@ -73,11 +73,11 @@ func main() {
 	// 3. Run the string against the NFA
 
 	if len(flag.Args()) < 1 { // flag.Args() also strips out program name
-		fmt.Println("ERROR: Missing cmdline args")
+		fmt.Printf("%s: ERROR: Missing cmdline args\n", os.Args[0])
 		os.Exit(22)
 	}
 	if *recursiveFlag && len(flag.Args()) < 2 { // File/Directory must be provided with '-r'
-		fmt.Println("ERROR: Missing cmdline args")
+		fmt.Printf("%s: ERROR: Missing cmdline args\n", os.Args[0])
 		os.Exit(22)
 	}
 	var re string
@@ -92,7 +92,16 @@ func main() {
 		for _, inputFilename := range inputFilenames {
 			inputFile, err := os.Open(inputFilename)
 			if err != nil {
-				fmt.Printf("%s: No such file or directory\n", inputFilename)
+				fmt.Printf("%s: %s: No such file or directory\n", os.Args[0], inputFilename)
+				os.Exit(2)
+			}
+			fileStat, err := inputFile.Stat()
+			if err != nil {
+				fmt.Printf("%v\n", err)
+				os.Exit(2)
+			}
+			if fileStat.Mode().IsDir() {
+				fmt.Printf("%s: %s: Is a directory\n", os.Args[0], inputFilename)
 				os.Exit(2)
 			}
 			inputFiles = append(inputFiles, inputFile)