add -h and -V (#23)

cmd/escargs/escargs.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
+	"log"
 	"os"
 
 	"github.com/alessio/shellescape"
@@ -17,22 +18,45 @@ var (
 	discardBlankLines bool
 	nullSeparator     bool
 	argFile           string
+	helpMode          bool
+	versionMode       bool
 )
 
-func main() {
+var version = "UNRELEASED"
+
+func init() {
 	flag.BoolVar(&discardBlankLines, "D", false, "ignore blank lines on the input stream.")
 	flag.BoolVar(&nullSeparator, "0", false, "input items are terminated by a null character instead of by new line.")
 	flag.StringVar(&argFile, "a", "", "read arguments from file, not standard input.")
+	flag.BoolVar(&helpMode, "h", false, "display this help and exit.")
+	flag.BoolVar(&versionMode, "V", false, "output version information and exit.")
+	flag.Usage = usage
+	flag.ErrHelp = nil
+}
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("escargs: ")
+	log.SetOutput(os.Stderr)
 	flag.Parse()
 
+	if helpMode {
+		usage()
+		return
+	}
+
+	if versionMode {
+		outputVersion()
+		return
+	}
+
 	firstScan := true
 	scanner := bufio.NewScanner(os.Stdin)
 
 	if argFile != "" {
 		f, err := os.Open(argFile)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "escargs: %v\n", err)
-			os.Exit(1)
+			log.Fatal(err)
 		}
 
 		scanner = bufio.NewScanner(f)
@@ -76,3 +100,18 @@ func splitNullTerminatedItems(data []byte, atEOF bool) (advance int, token []byt
 	// Request more data.
 	return 0, nil, nil
 }
+
+func usage() {
+	usageString := `Usage: escargs [-0ad]
+Escape arbitrary strings for safe use as command line arguments.
+		
+Options:`
+	_, _ = fmt.Fprintln(os.Stderr, usageString)
+
+	flag.PrintDefaults()
+}
+
+func outputVersion() {
+	fmt.Fprintf(os.Stderr, "escargs version %s\n", version)
+	fmt.Fprintln(os.Stderr, "Copyright (C) 2020-2023 Alessio Treglia <alessio@debian.org>")
+}