General difference between `stat` and `open` for files.

file.go

// This demonstrates a little bit of how Unix directories work, re late-night chat with Bujol about Facebook Haystack.
//
// (Go makes this clearer than languages like Python or Ruby generally do.)
package main

import (
	"bytes"
	"fmt"
	"go/doc"
	"log"
	"os"
)

var cwd string // current working directory

func init() {
	var err error
	if cwd, err = os.Getwd(); err != nil {
		log.Fatal(err)
	}
}

func main() {
	// Getting file info doesn't really require opening the file.
	fi, err := os.Stat(cwd)
	if err != nil {
		log.Fatal(err)
	}
	log.Print(format(fi))

	// However, if you want to read contents, you have to open the file —
	// and a directory’s contents happen to be its file list.
	dir, err := os.Open(cwd)
	if err != nil {
		log.Fatal(err)
	}
	defer dir.Close()
	files, err := dir.Readdirnames(-1)
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("files in %s:\n", dir.Name())
	for _, f := range files {
		log.Printf("\t%s\n", f)
	}
}

// format is an absurdly unnecessary prettyprinter for FileInfo.
func format(fi os.FileInfo) string {
	var b bytes.Buffer
	fmt.Fprintf(&b, "file info for %s:\n", fi.Name())
	doc.ToText(&b, fmt.Sprintf("%#v", fi), "\t\t\t", "", 59)
	b.WriteByte('\n')
	return b.String()
}