Add fragment.go

cmd/fragment/fragment.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+
+	"github.com/kisom/die"
+)
+
+func usage() {
+	progname := filepath.Base(os.Args[0])
+	fmt.Printf(`Usage: %s 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.
+`, progname)
+}
+
+func main() {
+	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
+		}
+	}
+
+	if end < start {
+		fmt.Println("[!] end < start, swapping values")
+		tmp := end
+		end = start
+		start = tmp
+	}
+
+	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())
+	}
+
+	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++ {
+		fmt.Printf(fmtStr, i, lines[i])
+	}
+}