Don't compile the regex if no valid files were given (eg. all files are directories); print error if file is a binary file (contains NULL character)

kg/main.go

@@ -102,12 +102,19 @@ func main() {
 					if fileStat.Mode().IsDir() {
 						fmt.Printf("%s: %s: Is a directory\n", os.Args[0], inputFilename)
 					} else {
-						inputFiles = append(inputFiles, inputFile)
+						if fileContainsNullChar(inputFile) {
+							fmt.Printf("%s: %s: Is a binary file\n", os.Args[0], inputFilename)
+						} else {
+							inputFiles = append(inputFiles, inputFile)
+						}
 					}
 				}
 			}
 		}
 	}
+	if len(inputFiles) == 0 { // No valid files given
+		os.Exit(2)
+	}
 
 	var test_str string
 	var err error