gistfile1.txt

package main

import (
	b "bufio"
	f "fmt"
	l "log"
	"os"
	r "regexp"
	"strconv"
)

func intify(s string) int {
	n, err := strconv.Atoi(s)
	if err != nil {
		l.Fatal(err)
	}
	return n
}

func main() {
	scanner := b.NewScanner(os.Stdin)

	regex := r.MustCompile("(.*)\t(.*)/(.*)/(.*)")

	for scanner.Scan() {
		line := scanner.Text()
		matches := regex.FindStringSubmatch(line)
		if len(matches) != 0 {
			year := intify(matches[4])
			month := intify(matches[3])
			day := intify(matches[2])
			f.Printf("%s\t%04d-%02d-%02d\n", matches[1], year, month, day)
		} else {
			f.Println("no match")
		}
	}

	if err := scanner.Err(); err != nil {
		l.Fatal(err)
	}
}