Create a simple cli opts parser.

cat/main.go

@@ -14,30 +14,39 @@ func Fail(err error, format string, v ...any) {
   os.Exit(1)
 }
 
-func main() {
+type Opts struct {
-  var number bool
+  Number bool
-  var squeeze bool
+  Squeeze bool
+  Filename string
+}
 
-  flag.BoolVar(&number, "n", false, "Number all nonempty output lines, starting with 1")
+func parse_opts() (Opts) {
-  flag.BoolVar(&number, "number", false, "Number all nonempty output lines, starting with 1")
+  var opts Opts
-  flag.BoolVar(&squeeze, "s", false, "Suppress repeated adjacnet blank lines")
+
-  flag.BoolVar(&squeeze, "squeeze-blank", false, "Suppress repeated adjacnet blank lines")
+  flag.BoolVar(&opts.Number, "n", false, "Number all nonempty output lines, starting with 1")
+  flag.BoolVar(&opts.Squeeze, "s", false, "Suppress repeated adjacent blank lines")
   flag.Parse()
 
   if flag.NArg() < 1 {
-    log.Fatal("USAGE: cat [-n/--number] file0 [fileN]")
+    log.Fatal("USAGE: cat [-n] [-s] file0 [fileN]")
     os.Exit(1)
   }
 
-  filename := flag.Arg(0)
+  opts.Filename = flag.Arg(0)
-  in_file, err := os.ReadFile(filename)
+
+  return opts
+}
+
+func main() {
+  opts := parse_opts()
+  in_file, err := os.ReadFile(opts.Filename)
 
-  if err != nil { Fail(err, "cannot open %s:", filename) }
+  if err != nil { Fail(err, "cannot open %s:", opts.Filename) }
 
-  if(number) {
+  if(opts.Number) {
     count := 1
     for line := range strings.Lines(string(in_file)) {
-      if squeeze && len(line) <= 1 {
+      if opts.Squeeze && len(line) <= 1 {
         continue
       }