input.go

// Writes stdin to output.log
package main

import (
  "os"
  "io"
)

func main() {
  output, err := os.Create("output.log")
  if err != nil {
    panic(err)
  }
  defer output.Close()

  _, err = io.Copy(output, os.Stdin)
  if err != nil {
    panic(err)
  }
}

tail.go

// Prints when output.log is modified
package main

import (
  "fmt"
  "github.com/howeyc/fsnotify"
)

func main() {
  watcher, err := fsnotify.NewWatcher()
  if err != nil {
    panic(err)
  }
  defer watcher.Close()

  go func() {
    for {
      select {
      case err := <-watcher.Error:
        if err != nil {
          panic(err)
        }
      case ev := <-watcher.Event:
        fmt.Println(ev)
      }
    }
  }()

  err = watcher.Watch("output.log")
  if err != nil {
    panic(err)
  }

  select {}
}