JSON Formatter

json.go

package main

import (
  "encoding/json"
  "fmt"
  "io/ioutil"
  "os"
  "strings"
  "text/template"
)

func main() {
  data, err := ioutil.ReadAll(os.Stdin)
  if err != nil {
    fmt.Fprintf(os.Stderr, "reading stdin failed: %s", err)
    os.Exit(1)
  }

  v := make(map[string]interface{})
  err = json.Unmarshal(data, &v)
  if err != nil {
    fmt.Fprintf(os.Stderr, "invalid json: %s", err)
    os.Exit(2)
  }

  if len(os.Args) < 2 {
    out, err := json.MarshalIndent(v, "", "  ")
    if err != nil {
      fmt.Fprintf(os.Stderr, "failed to write json: %s", err)
      os.Exit(3)
    }
    fmt.Fprint(os.Stdout, string(out))
  } else {
    delimiter := ""
    for _, arg := range os.Args[1:] {
      fmt.Fprint(os.Stdout, delimiter)

      t := template.New("Arg")
      if strings.Contains(arg, "{{") {
        _, err = t.Parse(arg)
      } else {
        _, err = t.Parse(fmt.Sprintf("{{.%s}}", arg))
      }
      if err != nil {
        fmt.Fprintf(os.Stderr, "cannot parse template field: %s", err)
        continue
      }

      err = t.Execute(os.Stdout, v)
      if err != nil {
        fmt.Fprintf(os.Stderr, "failed to execute template: %s", err)
        os.Exit(3)
      }

      delimiter = "\n"
    }
  }
}