Go语言模仿linux cat命令

Go语言模仿linux cat命令

package main
import (
  "io"
  "os"
  "fmt"
  "bufio"
  "flag"
)
var numberFlag = flag.Bool("n", false, "number each line")
func cat(r *bufio.Reader) {
  i := 1
  for {
    buf, e := r.ReadBytes('\n')
    if e == io.EOF { 
      break
    }
    if *numberFlag {
      fmt.Fprintf(os.Stdout, "%5d %s", i, buf)
      i++
    } else {
      fmt.Fprintf(os.Stdout, "%s", buf)
    }
  }
  return
}
func main() {
  flag.Parse()
  if flag.NArg() == 0 {
    cat(bufio.NewReader(os.Stdin))
  }
  for i := 0; i < flag.NArg(); i++ {
    f, e := os.Open(flag.Arg(i))
    if e != nil {
      fmt.Fprintf(os.Stderr, "%s: error reading from %s: %s\n", os.Args[0], flag.Arg(i), e.Error())
      continue
    }
    cat(bufio.NewReader(f))
  }
}