From fc29cd896b8eed743b4d4732910eab433328451a Mon Sep 17 00:00:00 2001
From: Bart de Boer <bart.deboer@gmail.com>
Date: Fri, 3 May 2024 00:49:17 +0200
Subject: [PATCH 1/4] update First(n int) so that it can be used for user input

---
 script.go | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/script.go b/script.go
index ea70a56..b959334 100644
--- a/script.go
+++ b/script.go
@@ -522,13 +522,20 @@ func (p *Pipe) First(n int) *Pipe {
 	if n <= 0 {
 		return NewPipe()
 	}
-	i := 0
-	return p.FilterScan(func(line string, w io.Writer) {
-		if i >= n {
-			return
+	return p.Filter(func(r io.Reader, w io.Writer) error {
+		scanner := newScanner(r)
+		i := 0
+		for scanner.Scan() {
+			_, err := fmt.Fprintln(w, scanner.Text())
+			if err != nil {
+				return err
+			}
+			i++
+			if i >= n {
+				break
+			}
 		}
-		fmt.Fprintln(w, line)
-		i++
+		return scanner.Err()
 	})
 }
 
@@ -964,3 +971,10 @@ func newScanner(r io.Reader) *bufio.Scanner {
 	scanner.Buffer(make([]byte, 4096), math.MaxInt)
 	return scanner
 }
+
+// Prompt creates a pipe that reads user input from stdin after displaying the
+// specified prompt.
+func Prompt(prompt string) *Pipe {
+	fmt.Print(prompt)
+	return Stdin().First(1)
+}

From 819d15c4e9090793ec4165d8fea6adfdef0530b7 Mon Sep 17 00:00:00 2001
From: Bart de Boer <bart.deboer@gmail.com>
Date: Sun, 5 May 2024 14:27:54 +0200
Subject: [PATCH 2/4] make the update to First() more elegant and update
 comment as suggested by John

---
 script.go | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/script.go b/script.go
index b959334..007e9eb 100644
--- a/script.go
+++ b/script.go
@@ -514,7 +514,8 @@ func (p *Pipe) FilterScan(filter func(string, io.Writer)) *Pipe {
 
 // First produces only the first n lines of the pipe's contents, or all the
 // lines if there are less than n. If n is zero or negative, there is no output
-// at all.
+// at all. When n lines have been produced, First stops reading its input and
+// sends EOF to its output.
 func (p *Pipe) First(n int) *Pipe {
 	if p.Error() != nil {
 		return p
@@ -524,16 +525,11 @@ func (p *Pipe) First(n int) *Pipe {
 	}
 	return p.Filter(func(r io.Reader, w io.Writer) error {
 		scanner := newScanner(r)
-		i := 0
-		for scanner.Scan() {
+		for i := 0; i < n && scanner.Scan(); i++ {
 			_, err := fmt.Fprintln(w, scanner.Text())
 			if err != nil {
 				return err
 			}
-			i++
-			if i >= n {
-				break
-			}
 		}
 		return scanner.Err()
 	})

From 9d02069c529cb785e31974623cf6283243a53314 Mon Sep 17 00:00:00 2001
From: Bart de Boer <bart.deboer@gmail.com>
Date: Sun, 5 May 2024 14:28:46 +0200
Subject: [PATCH 3/4] remove the Prompt function

---
 script.go | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/script.go b/script.go
index 007e9eb..c471f74 100644
--- a/script.go
+++ b/script.go
@@ -967,10 +967,3 @@ func newScanner(r io.Reader) *bufio.Scanner {
 	scanner.Buffer(make([]byte, 4096), math.MaxInt)
 	return scanner
 }
-
-// Prompt creates a pipe that reads user input from stdin after displaying the
-// specified prompt.
-func Prompt(prompt string) *Pipe {
-	fmt.Print(prompt)
-	return Stdin().First(1)
-}

From 53ab797e9c41400c4afdd895d7d9ebbafaa78fdb Mon Sep 17 00:00:00 2001
From: Bart de Boer <bart.deboer@gmail.com>
Date: Sun, 5 May 2024 22:50:39 +0200
Subject: [PATCH 4/4] add test TestFirstDoesNotConsumeUnnecessaryData

---
 script_test.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/script_test.go b/script_test.go
index dd12e3b..b19b915 100644
--- a/script_test.go
+++ b/script_test.go
@@ -573,6 +573,24 @@ func TestFirstHasNoEffectGivenLessThanNInputLines(t *testing.T) {
 	}
 }
 
+func TestFirstDoesNotConsumeUnnecessaryData(t *testing.T) {
+	t.Parallel()
+	// First uses a 4096-byte buffer, so will always read at least
+	// that much, but no more (once N lines have been read).
+	r := strings.NewReader(strings.Repeat("line\n", 1000))
+	got, err := script.NewPipe().WithReader(r).First(1).String()
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := "line\n"
+	if want != got {
+		t.Errorf("want output %q, got %q", want, got)
+	}
+	if r.Len() == 0 {
+		t.Errorf("no data left in reader")
+	}
+}
+
 func TestFreqHandlesLongLines(t *testing.T) {
 	t.Parallel()
 	got, err := script.Echo(longLine).Freq().Slice()