434 Add Command to Tail -n Lines #544

CodeZea1ot · 2024-04-22T21:00:08Z

Closes #434

Changes

Adds a new gum tail subcommand
Allows user to stream stdin for -n number of lines
Keeps logs from piped running processes from cluttering up the terminal

Example

{ sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3 // Stream the last 3 lines of info generated by this process until complete

maaslalani · 2024-04-22T21:45:41Z

Hey @CodeZea1ot, thanks so much for the contribution!

What benefit do you get with gum tail vs simply using tail?

CodeZea1ot · 2024-04-22T22:19:52Z

Hey there @maaslalani

The idea behind a gum tail is to be able to stream output from a long running process that produces a lot of output with a configurable amount of visible max lines.

For example, say you have a script that runs an install or download process that you don't want to hide with gum spin, you could instead show the last -n lines of the output to the user, with it refreshing until the process ends.

In other words, you would get up to -n lines of output at all times and those lines that are displayed would always show the latest lines from the piped command coming into stdin.

Recording.2024-04-22.181848.mp4

newcron · 2024-04-26T14:53:41Z

I have to say, that's one of the features I'm waiting for so that I can start to use it.

My usecase is a local dev environment in which several automated steps are performed to simplify the dev process.

in my case, I would love exactly that for my build script, which should: build the code, create a test environment (databases with fixtures,...), then start the application and then run the end to end tests.

Each of these steps produces output, which I don't want the whole screen to pollute. at the same time, it would be very useful for the developers to get a glimpse on what's going on (e.g. if there is an error in the build, or the application crashes at startup).

Filling the whole screen with that just feels too verbose, yet not showing at all leaves the user without any sense of real progress.

CodeZea1ot · 2024-04-26T17:26:16Z

I built a BASH CLI called spyglass for this use case. You can check it out over at https://github.com/CodeZea1ot/spyglass

This is the functionality I'd like to bring to a gum tail command.

caarlos0

made some suggestions

also would be good to run goimports/gofmt

caarlos0 · 2024-07-25T14:17:45Z

gum.go

+	// Tail
+	// Provides a means of streaming -n of lines from stdin


Suggested change

// Tail

// Provides a means of streaming -n of lines from stdin

// Tail provides a means of streaming a number of lines from stdin.

Suggested change applied in 0087173

caarlos0 · 2024-07-25T14:18:10Z

gum.go


+	// Tail
+	// Provides a means of streaming -n of lines from stdin
+	// Useful for showing a subset of output from a process without clogging up the terminal


Suggested change

// Useful for showing a subset of output from a process without clogging up the terminal

// It is useful for showing a subset of output from a process without clogging up the terminal.

Suggested change applied in 0087173

caarlos0 · 2024-07-25T14:19:05Z

gum.go

+	// Provides a means of streaming -n of lines from stdin
+	// Useful for showing a subset of output from a process without clogging up the terminal
+	//
+	// $ { sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3


Suggested change

// $ { sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3

// Let's watch apt update:

//

// $ { sudo apt update -y && sudo apt upgrade -y && sudo apt autoremove -y; } | gum tail -n 3

Suggested change applied in 0087173

caarlos0 · 2024-07-25T14:20:46Z

tail/command.go

+	"os"
+)
+
+// Run executes the tail command


Suggested change

// Run executes the tail command

// Run executes the tail command.

Suggested change applied in 0087173

caarlos0 · 2024-07-25T14:24:38Z

tail/command.go

+}
+
+func clearScreen() {
+    fmt.Print("\033[H\033[2J")


Suggested change

fmt.Print("\033[H\033[2J")

fmt.Print(ansi.EraseDisplay(2))

#544 (comment)

caarlos0 · 2024-07-25T14:25:22Z

tail/command.go

+    start := len(lines) - n
+    if start < 0 {
+        start = 0
+    }
+    for i := start; i < len(lines); i++ {
+        fmt.Println(lines[i])
+    }


Suggested change

start := len(lines) - n

if start < 0 {

start = 0

}

for i := start; i < len(lines); i++ {

fmt.Println(lines[i])

}

fmt.Println(strings.Join(lines, "\n"))

Refactored in 45e1406

See following comment #544 (comment)

reitzig · 2025-09-10T10:08:41Z

tail/command.go

+    // Continuously read lines from stdin and update the last n lines
+    for line := range lines {
+        lastLines = appendLine(lastLines, line, o.NumLines)
+        clearScreen()


❔ Can we put clearScreen() behind an option?

I'd prefer the behaviour shown in #434.1967362421, i.e. gum tail would leave the screen content "above" alone, and only update its "own" N lines.

I think this refactor solves the clear screen problem and improves the functionality of the tail command.

45e1406

Screencast.from.09-11-2025.10.36.47.AM.webm

reitzig · 2025-09-10T10:09:51Z

Is there anything beyond above comments by @caarlos0 preventing this from being merged?

CodeZea1ot added 3 commits April 17, 2024 21:24

Init tail command files

3462555

Add tail subcommand

d97136e

Update doc with tail subcommand

1f48244

CodeZea1ot requested a review from maaslalani as a code owner April 22, 2024 21:00

caarlos0 reviewed Jul 25, 2024

View reviewed changes

reitzig reviewed Sep 10, 2025

View reviewed changes

Run formatter

ee9081e

CodeZea1ot requested a review from a team as a code owner September 11, 2025 13:30

CodeZea1ot requested review from andreynering and meowgorithm and removed request for a team and maaslalani September 11, 2025 13:30

Tyler W. Phass (Code Zealot) added 2 commits September 11, 2025 09:35

Update comments

0087173

Isolate tail behavior to its input

45e1406

		// Tail
		// Provides a means of streaming -n of lines from stdin

	// Tail
	// Provides a means of streaming -n of lines from stdin
	// Tail provides a means of streaming a number of lines from stdin.

	// Useful for showing a subset of output from a process without clogging up the terminal
	// It is useful for showing a subset of output from a process without clogging up the terminal.

	// Run executes the tail command
	// Run executes the tail command.

434 Add Command to Tail -n Lines #544

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434 Add Command to Tail -n Lines #544

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CodeZea1ot commented Apr 22, 2024

Changes

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CodeZea1ot commented Apr 22, 2024

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reitzig commented Sep 10, 2025

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maaslalani commented Apr 22, 2024 •

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