tu.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"os"
)

func die(s string, v ...interface{}) {
	fmt.Fprintf(os.Stderr, "tu: ")
	fmt.Fprintf(os.Stderr, s, v...)
	fmt.Fprintf(os.Stderr, "\n")
	os.Exit(1)
}
func main() {
	flag.Parse()
	if 1 > flag.NArg() {
		die("missing operand")
	}
	if 2 > flag.NArg() {
		die("missing operand after `%s'", flag.Arg(0))
	}
	if 2 < flag.NArg() {
		die("extra operand after `%s'", flag.Arg(1))
	}
	tab := make(map[rune]rune)
	set1 := []rune(flag.Arg(0))
	set2 := []rune(flag.Arg(1))
	j := 0
	for i := 0; i < len(set1); i++ {
		tab[set1[i]] = set2[j]
		if j < len(set2)-1 {
			j++
		}
	}
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	flush := func() {
		if er := out.Flush(); er != nil {
			die("flush: %s", er.Error())
		}
	}
	writeRune := func(r rune) {
		if _, er := out.WriteRune(r); er != nil {
			die("write: %s", er.Error())
		}
	}
	for done := false; !done; {
		switch r, _, er := in.ReadRune(); er {
		case io.EOF:
			done = true
		case nil:
			if s, found := tab[r]; found {
				writeRune(s)
			} else {
				writeRune(r)
			}
			if '\n' == r {
				flush()
			}
		default:
			die("%s: %s", os.Stdin.Name(), er.Error())
		}
	}
	flush()
}