package main

import "bufio"
import "io"
import "log"
import "os"
import "strings"

func transform(in io.Reader, out io.Writer) {
	bufw := bufio.NewWriter(out)
	s := bufio.NewScanner(in)
	for s.Scan() {
		line := s.Text()
		for i, c := range line {
			if i == 0 {
				bufw.WriteString(strings.ToLower(string(c)))
			} else {
				bufw.WriteString(string(c))
			}
		}
		bufw.WriteString("\n")
	}
}

func main() {
	if len(os.Args) < 2 {
		log.Fatalln("Usage upper-line <file>")
	}
	f, err := os.Open(os.Args[1])
	if err != nil {
		log.Fatalln("Error opening file", err)
	}
	defer f.Close()

	var w io.Writer
	if len(os.Args) >= 3 {
		w, err = os.Create(os.Args[2])
		if err != nil {
			log.Fatalln("Error creating file", err)
		}
	} else {
		w = os.Stdout
	}

	transform(f, w)
}