Added extra check if fileContainsNullChar returns err; pass filename to it instead of file

.gitignore

@@ -1,2 +1 @@
-re
+kg/kg
-

README.md

@@ -15,3 +15,7 @@ It also includes features not present in regexp, such as lookarounds and backref
 The syntax is, for the most part, a superset of Go's regexp. A full overview of the syntax can be found [here](https://pkg.go.dev/gitea.twomorecents.org/Rockingcool/kleingrep/regex#hdr-Syntax).
 
 __For more information, see https://pkg.go.dev/gitea.twomorecents.org/Rockingcool/kleingrep/regex__.
+
+### How it works
+
+I've written about the inner workings of the engine [on my blog](https://twomorecents.org/writing-regex-engine/index.html).

kg/helpers.go

@@ -1,6 +1,11 @@
 package main
 
-import "slices"
+import (
+	"bufio"
+	"os"
+	"slices"
+	"strings"
+)
 
 type character interface {
 	int | rune
@@ -25,3 +30,23 @@ func genRange[T character](start, end T) []T {
 	}
 	return toRet
 }
+
+// Returns whether or not the given file contains a NULL character
+func fileContainsNullChar(filename string) (bool, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return true, err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Contains(line, "\000") {
+			return true, nil
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return true, err
+	}
+	return false, nil
+}

kg/main.go

@@ -91,6 +91,7 @@ func main() {
 		inputFilenames := flag.Args()[1:]
 		for _, inputFilename := range inputFilenames {
 			inputFile, err := os.Open(inputFilename)
+			defer inputFile.Close()
 			if err != nil {
 				fmt.Printf("%s: %s: No such file or directory\n", os.Args[0], inputFilename)
 			} else {
@@ -101,6 +102,15 @@ func main() {
 				} else {
 					if fileStat.Mode().IsDir() {
 						fmt.Printf("%s: %s: Is a directory\n", os.Args[0], inputFilename)
+					} else {
+						var nullCharPresent bool
+						if nullCharPresent, err = fileContainsNullChar(inputFilename); nullCharPresent {
+							if err != nil {
+								fmt.Printf("%v\n", err)
+								os.Exit(1)
+							} else {
+								fmt.Printf("%s: %s: Is a binary file\n", os.Args[0], inputFilename)
+							}
 						} else {
 							inputFiles = append(inputFiles, inputFile)
 						}
@@ -108,6 +118,10 @@ func main() {
 				}
 			}
 		}
+	}
+	if len(inputFiles) == 0 { // No valid files given
+		os.Exit(2)
+	}
 
 	var test_str string
 	var err error