From 355b99d3054e86fbe47b3064b4ad736faac12e70 Mon Sep 17 00:00:00 2001
From: Viacheslav Poturaev <vearutop@gmail.com>
Date: Thu, 29 Oct 2026 10:43:26 +0100
Subject: [PATCH] Add in place progress print

---
 cmd/catp/README.md    |  1 +
 cmd/catp/catp/app.go  |  4 +++-
 cmd/catp/catp/catp.go |  5 +++--
 progress.go           | 31 ++++++++++++++++++++++++++++++-
 4 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/cmd/catp/README.md b/cmd/catp/README.md
index 3275429..32ac3e5 100644
--- a/cmd/catp/README.md
+++ b/cmd/catp/README.md
@@ -38,6 +38,7 @@ catp [OPTIONS] PATH ...
         POST /rate-limit?value=X sets a new one (0 or less means unlimited)
   -http-auth string
         user:pass to require as HTTP basic auth for -http endpoints
+  -i    rewrite progress line in place (terminal only)
   -l    count lines
   -no-progress
         disable progress printing
diff --git a/cmd/catp/catp/app.go b/cmd/catp/catp/app.go
index 8f2a5cc..dcc4f09 100644
--- a/cmd/catp/catp/app.go
+++ b/cmd/catp/catp/app.go
@@ -95,6 +95,7 @@ func Main(options ...func(o *Options)) error { //nolint:funlen,cyclop,gocognit,g
 	cpuProfile := flag.String("dbg-cpu-prof", "", "write first 10 seconds of CPU profile to file")
 	memProfile := flag.String("dbg-mem-prof", "", "write heap profile to file after 10 seconds")
 	output := flag.String("output", "", "output to file (can have .gz or .zst ext for compression) instead of STDOUT")
+	flag.BoolVar(&r.progressInPlace, "i", false, "rewrite progress line in place (terminal only)")
 	flag.BoolVar(&r.noProgress, "no-progress", false, "disable progress printing")
 	flag.BoolVar(&r.countLines, "l", false, "count lines")
 	flag.Float64Var(&r.rateLimit, "rate-limit", 0, "output rate limit lines per second")
@@ -228,9 +229,10 @@ func Main(options ...func(o *Options)) error { //nolint:funlen,cyclop,gocognit,g
 				return
 			}
 
-			println(s)
+			r.pr.Println(s)
 		},
 	}
+	r.pr.InPlace = r.progressInPlace
 
 	for _, fn := range files {
 		if fn == "-" {
diff --git a/cmd/catp/catp/catp.go b/cmd/catp/catp/catp.go
index b899a28..e2686a0 100644
--- a/cmd/catp/catp/catp.go
+++ b/cmd/catp/catp/catp.go
@@ -78,8 +78,9 @@ type runner struct {
 	lastStatus string
 	speed      []speedSample // Kept only with -http, for the status page charts.
 
-	noProgress bool
-	countLines bool
+	noProgress      bool
+	progressInPlace bool
+	countLines      bool
 
 	startLine int
 	endLine   int
diff --git a/progress.go b/progress.go
index 4654e14..2c4f5cf 100644
--- a/progress.go
+++ b/progress.go
@@ -4,6 +4,7 @@ package progress
 import (
 	"fmt"
 	"io"
+	"os"
 	"runtime"
 	"sync"
 	"sync/atomic"
@@ -35,6 +36,9 @@ type Progress struct {
 	// IncrementalSpeed shows speed and remaining estimate based on performance between two status updates.
 	IncrementalSpeed bool
 
+	// InPlace rewrites the status line in place instead of appending lines, only effective if stderr is a terminal.
+	InPlace bool
+
 	done    chan bool
 	task    Task
 	lines   func() int64
@@ -150,7 +154,7 @@ func (p *Progress) Start(options ...func(t *Task)) {
 	p.prnt = p.Print
 	if p.prnt == nil {
 		p.prnt = func(s Status) {
-			println(DefaultStatus(s))
+			p.Println(DefaultStatus(s))
 		}
 	}
 
@@ -266,10 +270,35 @@ func (p *Progress) printStatus(last bool) {
 	}
 }
 
+// Println prints a status line to stderr, honoring InPlace.
+func (p *Progress) Println(s string) {
+	if p.inPlace() {
+		print("\r" + s + "\033[K") // \033[K erases leftovers of a longer previous line.
+
+		return
+	}
+
+	println(s)
+}
+
+func (p *Progress) inPlace() bool {
+	if !p.InPlace {
+		return false
+	}
+
+	st, err := os.Stderr.Stat()
+
+	return err == nil && st.Mode()&os.ModeCharDevice != 0
+}
+
 // Stop stops progress reporting.
 func (p *Progress) Stop() {
 	p.printStatus(true)
 
+	if p.inPlace() {
+		println() // Keep the final status and move to a fresh line.
+	}
+
 	if !p.task.Continue {
 		p.metrics = nil
 	}