Add start/end line

Author: vearutop

cmd/catp/catp/app.go

@@ -79,6 +79,11 @@ func Main(options ...func(o *Options)) error { //nolint:funlen,cyclop,gocognit,g
 		"files will be written to out dir with original base names\n"+
 		"disables output flag")
 
+	flag.IntVar(&r.startLine, "start-line", 0, "start printing lines from this line (inclusive),\n"+
+		"default is 0 (first line), each input file is counted separately")
+	flag.IntVar(&r.endLine, "end-line", 0, "stop printing lines at this line (exclusive),\n"+
+		"default is 0 (no limit), each input file is counted separately")
+
 	flag.Usage = func() {
 		fmt.Println("catp", version.Module("github.com/bool64/progress").Version+",",
 			version.Info().GoVersion, strings.Join(versionExtra, " "))

cmd/catp/catp/catp.go

@@ -59,6 +59,9 @@ type runner struct {
 	noProgress bool
 	countLines bool
 
+	startLine int
+	endLine   int
+
 	hasOptions bool
 	options    Options
 
@@ -200,6 +203,7 @@ func (r *runner) scanFile(filename string, rd io.Reader, out io.Writer) {
 	s := bufio.NewScanner(rd)
 	s.Buffer(make([]byte, 64*1024), 10*1024*1024)
 
+	fileLines := 0
 	lines := 0
 	buf := make([]byte, 64*1024)
 
@@ -213,8 +217,17 @@ func (r *runner) scanFile(filename string, rd io.Reader, out io.Writer) {
 	})
 
 	for s.Scan() {
+		fileLines++
 		lines++
 
+		if r.startLine > 0 && fileLines <= r.startLine {
+			continue
+		}
+
+		if r.endLine > 0 && fileLines > r.endLine {
+			break
+		}
+
 		if atomic.LoadInt64(&r.closed) > 0 {
 			break
 		}
@@ -399,6 +412,10 @@ func (r *runner) cat(filename string) (err error) { //nolint:gocyclo
 		r.limiter = rate.NewLimiter(rate.Limit(r.rateLimit), 100)
 	}
 
+	if r.startLine != 0 || r.endLine != 0 {
+		r.countLines = true
+	}
+
 	if r.filters.isSet() || r.parallel > 1 || r.hasOptions || r.countLines || r.rateLimit > 0 {
 		r.scanFile(filename, rd, out)
 	} else {