434 Add Command to Tail -n Lines

README.md

@@ -97,6 +97,7 @@ go install github.com/charmbracelet/gum@latest
   * [`spin`](#spin): Display spinner while running a command
   * [`style`](#style): Apply coloring, borders, spacing to text
   * [`table`](#table): Render a table of data
+  * [`tail`](#tail): Provides a means of streaming -n of lines from stdin
   * [`write`](#write): Prompt for long-form text
   * [`log`](#log): Log messages to output
 
@@ -262,6 +263,14 @@ gum style \
 
 <img src="https://github.com/charmbracelet/gum/assets/42545625/67468acf-b3e0-4e78-bd89-360739eb44fa" width="600" alt="Bubble Gum, So sweet and so fresh!" />
 
+## Tail
+
+Render a subset of lines from stdin for easy log monitoring without cluttering the terminal output.
+
+```bash
+{ sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3
+```
+
 ## Join
 
 Combine text vertically or horizontally. Use this command with `gum style` to

gum.go

@@ -17,6 +17,7 @@ import (
 	"github.com/charmbracelet/gum/spin"
 	"github.com/charmbracelet/gum/style"
 	"github.com/charmbracelet/gum/table"
+	"github.com/charmbracelet/gum/tail"
 	"github.com/charmbracelet/gum/write"
 )
 
@@ -196,6 +197,16 @@ type Gum struct {
 	//
 	Table table.Options `cmd:"" help:"Render a table of data"`
 
+	// Tail provides a means of streaming a number of lines from stdin
+	//
+	// It is useful for showing a subset of output from a process without clogging up the terminal.
+	//
+	// Let's watch apt update:
+	//
+	// $ { sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3
+	//
+	Tail tail.Options `cmd:"" help:"Tail the -n of lines from stdin"`
+
 	// Write provides a shell script interface for the text area bubble.
 	// https://github.com/charmbracelet/bubbles/tree/master/textarea
 	//

tail/command.go

@@ -0,0 +1,58 @@
+package tail
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+// Run executes the tail command.
+func (o Options) Run() error {
+	linesChan := make(chan string)
+
+	go func() {
+		scanner := bufio.NewScanner(os.Stdin)
+		for scanner.Scan() {
+			linesChan <- scanner.Text()
+		}
+		close(linesChan)
+	}()
+
+	lastLines := make([]string, 0, o.NumLines)
+	frameHeight := 0
+
+	for line := range linesChan {
+		lastLines = appendLine(lastLines, line, o.NumLines)
+
+		// Clear previous frame
+		if frameHeight > 0 {
+			fmt.Printf("\033[%dA", frameHeight) // Move cursor up
+		}
+
+		// Print current frame
+		for _, l := range lastLines {
+			fmt.Printf("\r\033[K%s\n", l) // Clear line + print
+		}
+
+		frameHeight = len(lastLines)
+	}
+
+	// After finishing, clear the live frame and print only final lines
+	if frameHeight > 0 {
+		fmt.Printf("\033[%dA", frameHeight)
+	}
+	fmt.Print("\033[J") // Clear everything below cursor
+	for _, l := range lastLines {
+		fmt.Println(l)
+	}
+
+	return nil
+}
+
+func appendLine(lines []string, line string, maxLines int) []string {
+	lines = append(lines, line)
+	if len(lines) > maxLines {
+		lines = lines[1:]
+	}
+	return lines
+}

tail/options.go

@@ -0,0 +1,5 @@
+package tail
+
+type Options struct {
+	NumLines int `short:"n" default:"4" help:"Number of lines you want to tail"`
+}