brew install go

package github.com/davecgh/go-spew/spew: cannot download, $GOPATH not set. For more details see: go help gopath

export GOPATH=$HOME/go/third-party:$HOME/go/my-project
export PATH=$HOME/go/third-party/bin:$HOME/go/my-project/bin:$PATH # binをPATHに追加するのも忘れずに

# -d オプションで、diffを表示してくれる
$ gofmt -d -r 'Zen2han -> Zen2Han' .
diff util/util.go gofmt/util/util.go
--- /var/folders/cy/nds3c8y97nsb8p6l416w5__w0000gn/T/gofmt327353297     2014-08-14 19:29:31.000000000 +0900
+++ /var/folders/cy/nds3c8y97nsb8p6l416w5__w0000gn/T/gofmt979152124     2014-08-14 19:29:31.000000000 +0900
@@ -24,7 +24,7 @@
 }

 // 全角英数字を半角に変換する
-func Zen2han(src string) string {
+func Zen2Han(src string) string {
        retbuf := make([]rune, 0, utf8.RuneCountInString(src))
        for _, ch := range src {
                if ch >= 0xFF21 && ch <= 0xFF3A {
@@ -60,5 +60,5 @@
 }

 func NormalizeStr(src string) string {
-       return Hiragana2Katakana(Zen2han(src))
+       return Hiragana2Katakana(Zen2Han(src))
 }

# 実際に書き換えるには、 -w オプション
$ gofmt -w -r 'Zen2han -> Zen2Han' .

package main

import (
  "fmt"

  "github.com/davecgh/go-spew/spew"
)

func main() {
  a := struct {
      A []string
      n int
  }{
      A: []string{"a", "b", "c"},
      n: 123,
  }

  fmt.Println("--- fmt.Printf ---")
  fmt.Printf("%#v\n", a)
  fmt.Println("--- spew.Dump ---")
  spew.Dump(a)
}

--- fmt.Printf ---
struct { A []string; n int }{A:[]string{"a", "b", "c"}, n:123}
--- spew.Dump ---
(struct { A []string; n int }) {
 A: ([]string) (len=3 cap=3) {
  (string) (len=1) "a",
  (string) (len=1) "b",
  (string) (len=1) "c"
 },
 n: (int) 123
}