package main import ( "bufio" "flag" "fmt" "os" "path/filepath" "strconv" "github.com/kisom/goutils/die" ) func usage() { progname := filepath.Base(os.Args[0]) fmt.Printf(`Usage: %s [-nl] file start [end] Print a fragment of a file starting a line 'start' and ending at line 'end', or EOF if no end is specified. The -nl flag will suppress printing of line numbers. `, progname) } func main() { quiet := flag.Bool("nl", false, "No line-numbering.") flag.Parse() if flag.NArg() < 2 || flag.NArg() > 3 { usage() os.Exit(1) } start, err := strconv.Atoi(flag.Arg(1)) die.If(err) var end int var offset bool if flag.NArg() == 3 { endStr := flag.Arg(2) if endStr[0] == '+' { offset = true endStr = endStr[1:] } end, err = strconv.Atoi(endStr) die.If(err) if offset { end += start } } file, err := os.Open(flag.Arg(0)) die.If(err) defer file.Close() scanner := bufio.NewScanner(file) // initial empty line to start numbering at 1. var lines = make([]string, 1) for scanner.Scan() { lines = append(lines, scanner.Text()) } if end == 0 { end = len(lines) - 1 } if end < start { fmt.Fprintln(os.Stderr, "[!] end < start, swapping values") tmp := end end = start start = tmp } var fmtStr string if !*quiet { maxLine := fmt.Sprintf("%d", len(lines)) fmtStr = fmt.Sprintf("%%0%dd: %%s", len(maxLine)) } endFunc := func(n int) bool { if n == 0 { return false } if n > end { return true } return false } fmtStr += "\n" for i := start; !endFunc(i); i++ { if *quiet { fmt.Println(lines[i]) } else { fmt.Printf(fmtStr, i, lines[i]) } } }