Now implemented a basic od command.

od/go.mod

@@ -0,0 +1,3 @@
+module git.learnjsthehardway.com/learn-code-the-hard-way/go-coreutils/od
+
+go 1.24.2

od/main.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+  "fmt"
+  "os"
+  "flag"
+  "log"
+  "bufio"
+)
+
+func Fail(err error, format string, v ...any) {
+  err_format := fmt.Sprintf("ERROR: %v; %s", err, format)
+  log.Printf(err_format, v...)
+  os.Exit(1)
+}
+
+type Opts struct {
+  Width int
+  Filenames []string
+  Hex bool
+  Octal bool
+  Format string
+}
+
+func parse_opts() (Opts) {
+  var opts Opts
+
+  flag.IntVar(&opts.Width, "w", 16, "Width of output grid")
+  flag.BoolVar(&opts.Hex, "x", false, "Output hex bytes")
+  flag.BoolVar(&opts.Octal, "o", false, "Output octal bytes")
+
+  flag.Parse()
+
+  if flag.NArg() == 0 {
+    log.Fatal("USAGE: od [files]")
+    os.Exit(1)
+  }
+
+  if opts.Hex {
+    opts.Format = "%0.2x "
+  } else {
+    opts.Format = "%0.3o "
+  }
+
+  opts.Filenames = flag.Args()
+  return opts
+}
+
+func main() {
+  opts := parse_opts()
+
+  for _, filename := range opts.Filenames {
+    reader, err := os.Open(filename)
+    defer reader.Close()
+    if err != nil { Fail(err, "can't open: %s", filename) }
+
+    buf := bufio.NewReader(reader)
+    count := buf.Size()
+
+    fmt.Printf("%0.8o ", 0);
+
+    for index := 0; index < count; index++ {
+      data, err := buf.ReadByte()
+      if err != nil { break }
+      fmt.Printf(opts.Format, data);
+
+      if (index + 1) % opts.Width == 0 {
+        fmt.Print("\n")
+        fmt.Printf("%0.8o ", index);
+      }
+    }
+  }
+}