Terminal tools

S02 E10


Terminal tools - a devtools discussion with Michelle Lim & Zach Lloyd (Warp). Episode 10 (Season 2) of the Console Devtools Podcast.

Episode notes

In this episode we speak to Michelle Lim and Zach Lloyd, both of Warp, a terminal designed to make developer workflows more productive. We discuss the historical significance of physical terminals, terminal emulators, pseudo-terminals and the shell. We also explore why Rust is a better technology choice than Electron for building a new terminal, why GPU acceleration matters, how it works with the macOS Metal APIs, and discuss the challenges garbage collection brings to high performance UIs.

Things mentioned:

About Michelle Lim & Zach Lloyd

Zach Lloyd is the founder and CEO of Warp, a Rust-based terminal for developers. Michelle is a software engineer who joined early on. Prior to Warp Zach co-founded SelfMade, was CTO at Time Inc., and ran the Google Sheets team at Google. Michelle graduated from Yale and previously worked at Robinhood, Slack, and Facebook.


Zach: When you run a terminal today on your modern Mac, you're actually running a terminal emulator like you said, and that's a piece of software that is copying the behavior of that hardware. And so the terminal emulator, when you run or Warp or iTerm, it's an actual sort of native GUI app that runs on your Mac. It's pretending to be this piece of hardware. And it's pretending to do that at a pretty deep level.

David: Welcome to the Console Podcast. I'm David Mytton, co-founder of; a free weekly newsletter highlighting the best and most interesting tools for developers. In this episode, I speak with Michelle Limand Zach Lloyd , both of Warp; a terminal designed to make developer workflows more productive. We discuss the historical significance of physical terminals, terminal emulators, pseudo-terminals and the shell. Why rust is a better technology choice than Electron for building a new terminal. Why GPU acceleration matters, how it works with the MacOS metal APIs, and challenges garbage collection brings to high performance UIs. We're keeping this to 30 minutes. So let's get started. I'm here with Michelle Lim and Zach Lloyd. Michelle, Zach, thanks for joining the Console Podcast.

Michelle: Thank you for having us.

Zach: Thank you for having us.

David: Let's start with a brief background. Tell us a little about what you're currently doing and how you got here.

Zach: I'm Zach, I'm the founder and CEO of Warp. We are building a new terminal that is trying to modernize the product that is very, very widely used, but hasn't changed much in the last 40 years. The goal of it is to build a terminal that is more powerful than anything that's existed before, but also more accessible to all developers. And very briefly, my background, the way I got here is I was a engineer for quite a long time at Google. I used to run engineering on Google Sheets, and then I was a Principal Engineer on Google Docs. And I've been a terminal user for the last 20 years and always wondered why it worked the way that it does and was excited to start a company around trying to build a product that I'd always wanted it to be.

**Michelle:**And my name is Michelle. I am an engineer on the Warp team and I had joined over a year ago when it was just Zach, the founder and designer CQ. I joined because when I was starting to learn coding, the terminal was one of the biggest blockers. And then as I started getting better at the terminal and started using Docker and Kubernetes, I realized that there were a lot of productivity blockers still. And so I wanted to co-build this experience that could make all developers from all backgrounds more productive. Before that, I graduated Gale and had interned at Facebook, Robinhood and Slack.

David: Let's start with the origin of the terminal, which is properly called a Terminal Emulator. What does that mean?

Zach:: I'm not a terminal historian, but the basic terminal was an actual hardware device. So if you look back maybe late sixties, early seventies, terminal was sort of the main interface to your actual computer. And what it was really was a device that allowed you to input characters. So you have a keyboard and input characters. And then on the other end, there would be something that would interpret those characters. And then it would send characters back to the terminal. And this all happened over a sort of serial line input.

And then what the terminal would do was interpret what came back and basically render the characters on a screen. And there was a, and actually still is a encoding that the terminal uses to know how to render those characters, which is a bunch of sort of escape sequences. And so for instance, if you want to tell the terminal to draw something in color, you basically the thing that's sending characters back would send back a bunch of characters that sort of surround the text that's being rendered. And then the terminal interprets that and draws it on the screen.

And so that all was physical hardware. And that's where terminals came from. When you run a terminal today on your modern Mac, you're actually running a terminal emulator like you said, and that's a piece of software that is copying the behavior of that hardware. And so the terminal emulator, when you run or Warp or iTerm, it's an actual sort of native GUI app that runs on your Mac. It's pretending to be this piece of hardware. And it's pretending to do that at a pretty deep level.

The sort of Mac based and Linux based OSs actually have something that looks like a device, which is called a pseudo-terminal, which your terminal app takes your keystrokes, sends them into that device. On the other end of that, you have a shell like Bash or csh that reads them out, writes characters back. And then the Mac app, iTerm terminal has the same parsing logic as one of these old hardware devices. The canonical one was a VT100, which was something that was made by the digital equipment corporation, and your terminal interprets those character codes and basically paints characters on the screen.

David: Why do you think that terminals stuck around for so long? What is it that makes it so powerful?

Michelle: Yeah. The terminal is a platform for running text based apps, and compared to GUIs, text based apps are much faster to build because there's no UI. You can configure and build an infinite number of options. It is composable, in that you can pipe output from one program into the input of another, and it's easily scriptable. And the terminal is keyboard driven, which is much more ergonomic for some developers. Historically though, even though the terminal is powerful, it is still very hard to get it. It is not discoverable. You have to memorize a lot of keyboard shortcuts and commands and Flex, but once you do master it, you can be very efficient. And that's probably why it's still stuck around.

David: You mentioned the idea of it being a platform. What does that mean to you? Why do you think that application should be built on top of the terminal?

Zach: The things that Michelle said touch on a lot of it. Text based apps have a lot of these inherent advantages of being composable and scriptable and easiest apps to write. And so, one way you can think about the terminal is it's a platform for running these apps. So in a similar way to iOS is a platform for running mobile apps or Linux is a platform, people are constantly writing these text based apps. They're distributing them. There are users on the other end who install them and who run them and who configure them. And so if you think of a terminal in a broad sense like that, it's a platform. It also is interesting as a platform in that, in the same way that you can kind of configure your phone or your desktop computer to work in a certain way, or even the web; you can install Chrome extensions. The terminal itself is very, very configurable.

And so there's a big ecosystem of projects out there that make the terminal better in one way or another. So for example, you can install a bunch of things that make it easier to complete commands. You can install things that make your terminal themeable, or that make session management and the terminal better like Tmax. You can install things to let you search through your history better like FCF. And so it's this kind of ecosystem where developers are contributing and trying to make sort of the running and installation and management of all these text based apps as seamless and powerful as possible.

David: How do you think about these as different layers? The shell, the terminal, where does that come in? How can you interact with those different layers?

The basic thing is the terminal is the thing that's emulating the device that I talked about at the beginning. And so it's responsible for characters in, and then it takes characters out and renders them on the screen. The shell is your kind of command interpreter. It's the thing that makes sense of those characters and it interfaces with the system and lets you sort of launch apps and route those apps outputs back to the terminal. And so the cool thing about the terminal shell interface is that it's all text based. And what that sort of allows is, when you run a terminal locally, you might Bash or csh, but it sets up very well to doing remote access to machines. So when you run something like SSH, the exact same protocol that works with running a shell locally, works with running a shell when you're on some machine in some cloud at some place.

And so I think it's a powerful system, but it also has made the terminal relatively hard to innovate on, because those two pieces of it; the terminal and the shell sort of need to move in lockstep, meaning there's a, it's not a super standardized interface, but a well-defined interface between the two of them. And so if you're building a terminal, you want to build it to respect the output of all the common shells. And then you also have to be aware that the shell that it's interacting with might not even be on the same machine that you're running the terminal on. So you can't really build... it's very hard to build a fully integrated thing that will actually work for developers current workflows.

David: What do you think about the limitations of all of that history? So having to have the antsy escape codes you mentioned, and the pseudo-terminal and the shell, and all these different layers; do you think that's had an impact on the ability to innovate over the years?

I do. I mean, so for Warp for instance, we're building a new terminal. We're trying to build it in a way that's backwards compatible, because if it's not there's a tremendous amount of: A; existing script that's been written in Bash and csh, which I think it'd be very difficult to break for developers. B; muscle memory. So there's just habits that people have in terms of using terminals and existing ecosystem and plugins. So I think the trick if you want to innovate in this area, is to find a way where you can be mostly backwards compatible, but also push the world forward. That's sort of a delicate balance to strike. I think if you try to go to straight to the ideal solution and rewrite everything at once, you're going to really have a hard time getting adoption. I don't know, Michelle, do you have any other thoughts on that?

Michelle: Yeah. So the current architecture is such that the terminal has no concept of what program is running, or anything that's really going on in the shell, all the terminal does, is it reads and writes bytes, and it displays characters according to those escape sequences. It is really hard to innovate on the terminal in that, the way that developers think about the terminal is in terms of groups of commands and their corresponding outputs. But the way that the architecture is set up is that the entire terminal is a grid of characters, a buffer of text. So at Warp what we did was, we hooked onto the shell's [inaudible 00:10:45] and pre-command hooks and send those bytes over to the terminal in the way that communicates when a previous output ends. And that's how we try and group the commands and outputs together. So it's easier for the user to navigate, but still the hard part is that we still have to have every grid implement of VT100 spec.

David: So you're trying to innovate with features like the [inaudible 00:11:11] to understand where the processes are running and their current state whilst maintaining compatibility with a spec that is several decades old.

Zach: That's exactly right. Michelle described it. It's the way that we try and innovate is by working within the framework of the existing shells and by configuring them to do a little bit more than they have traditionally done. And then on the Terminal side we try to push the UI forward, but in a way that doesn't break backwards compatible, it's tricky.

David: How have you approached the testing of that to make sure that you are not breaking backwards compatibility? Is a lot of manual work or have you managed to automate it in some way?

Zach: It's both. I think on the automation side, we have done something interesting where we've built our own integration test framework. So you can run, for Warp, you can essentially run a headless version of it that will run against different shell configurations. So meaning, we can launch Warp through GitHub actions on a MacCloud that will run against Bash at a particular version, csh for a particular version and try to test things like that. But we are far from having sort of complete coverage with that. And so we end up having to do decent amount of manual stuff as well. But the ideal world in my mind would be able to get as much integration test coverage with these other, basically by running it against all these different sort of shell combinations as possible. Kind of what people used to do with browser tests, where you would run it against IE, and you would run it against Chrome and you'd run it against Firefox.

Michelle: Yeah, another complexity is that we build our own text editor as the input area for the terminal. And what that means is that we have to reimplement all the keyboard shortcuts and bindings that developers are used to. So I remember the start of the year, I had to go through the entire list of index findings and link Control-A; okay, move cursor to the start of line, Control-E; move cursor to the end of the line. And that was pretty, pretty manual. And over time we've gotten a lot of feedback that we were missing one or two more shortcuts. And this morning I just pushed another shortcut that we missed. There is a lot of manual work as well.

David: The editor component for what sounds like is an interesting challenge. Can you walk us through the architecture of that and how you've approached designing what people might think is just a ubiquitous component that should be in any application, but you've implemented it in quite an interesting way.

Zach: The broader context here is, usually command editing is done at the shell layer, not the terminal layer. And so we've pulled it up to the terminal layer. And the advantage of doing that is that you can make an editing experience that matches what I think people expect from an editor these days. So it works much more like editor that you'd see in VS code than a command line editor. And so really what that means we have to do is, we have to buffer the input that goes into the shell. Whereas in a typical shell, every character goes into the shell and gets echoed back. In Warp, we sort of gather all the input and then send it into the shell. I guess the why that we did that was to get intuitive, something that matches what people are used to. And then also it gives us the ability to build really cool features and have sort of complete control.

So for instance, it lets us do multiple cursor editing like what you get in vs code, or we could build syntax highlighting. We haven't quite done it yet, but we could build code formatting, we could build code folding. So any sort of input interaction that requires a little bit of a richer GUI, we now have the ability to do, whereas if you're limited to the character grid and the editor in the shell, it's just you're not going to be able to do that. That's a why.

And then the sort of the how, the broader context is that we have our own UI framework that we've developed in Rust. And there isn't really an off the shelf editor component that we could sort of easily plug into that, because we're basically doing everything from defining what the elements are like, to constructing a scene, to actually running shader code that draws pixels on the screen using Metal. And so once that's the world you're living in, we went down the road of building the editor ourselves. I should say we did this in conjunction with Nathan Sobo, who has a different developer company, which is using similar code, but it's something that we want to open source and is totally kind of a homegrown UI system.

David: So the code base is in Rust, but you originally started using Electron, Webtech. Can you take us through the decisions behind that and why you decided to switch?

Michelle: Yeah, so we started first with Electron because our team has a background in Webtech and we thought that the iteration speed will be very fast. But as we started experimenting, we realized that binary size was too large and the performance was pretty slow. So I did a test where I started drawing 200 buttons on an HTML overlay and started scrolling our terminal and the scrolling was extremely slowed down. So we found ourselves slowed down by testing performance at every commit. And so even though code compilations faster, iterations faster, in the end our entire development speed was pretty slow. And so we started looking into native solutions. So we didn't want something that had garbage collection. So that meant we had to choose between C, C++ plus and Rust. And Rust just had strongest developer ergonomics. There are a lot of guarantees of memory safety, threat safety, and it's just as low level as C++. And so we could easily call into the C based APIs of the operating system.

David: Why did you want to avoid garbage collection?

Zach: My experience with UIs and garbage collected languages is that you, it's sort of unpredictable and you have a lack of control over when the garbage collector is going to do its thing. If you want sort of consistently smooth performance, and I think it's interesting we think about performance in terms of frame rate, which is probably not what terminal developers typically think of it. But we want perfectly smooth scrolling, perfectly reactive event handling.

If you're going to have a garbage collector that is deciding to sort of clean up objects in the middle of that, I feel that gives you unpredictable performance. We certainly saw that a bunch on Google Sheets when we were working with large data in the browser, that performance problems would be caused by us not having control of memory allocation and de-allocation. And so I think Rust as a super elegant solution to that, where it's safer than C++ the way that Rust lifetimes work, and you have a sort of guaranteed smoothness around it, and then you also have sort of complete control. So that's why we decided to go that direction.

David: And you've also implemented GPU acceleration. Why does a terminal, which is most the text need GPU acceleration?

Michelle: The terminal has to render oftentimes full screens of text output on very large screens. And there are many programs that will output this text very quickly, which means that you have to repaint all this text in the subsecond speed. And so it is pretty much extended across all terminals to have GPU acceleration. We think that rendering the GPU gives us more clock CPU cycles for our product features. And plus because our graphics primitives are pretty limited, writing the shader code will really easy and fast. It is currently only lesser than 300 lines of code and we've barely had to touch it since January.

David: That's implemented currently using MacOS's Metal API. Why did you choose that over OpenGL?

Zach: We looked at OpenGL. We decided to go with Metal. I would say prime primarily because it's the more officially supported tool or API I should say on Mac practicing the GPU. The biggest win for us with Metal has been around the debugging tools that you get through Xcode. So there's all sorts of instruments to let you sort of examine textures and understand your frame rate in a way that the tooling is not quite as good for OpenGL. The downside is if we had done OpenGL, we could probably do a one to one port to another platform. But like Michelle said, it's actually pretty wild. It's only 300 lines of shader code are needed to do all of the primitives in the Terminal, which if you think about them, it's really we render rectangles and rounded rectangles. We render icons and images, and we render glyphs. It doesn't take a ton of shader code. So we decided to go with a thing that has the best developer experience for the first platform we were launching on.

David: You mentioned that you shifted out of Electron as a desktop implementation of webtech. Did you give any thought to browser based webtech, especially with the popularity of compiling, something like Rust into web assembly these days?

Zach: The Answer is yes. The other major reason that we chose Rust besides just performance, and the community, and the niceness of the Rust development experience, is that Russ is pretty good for cross platform. And the second platform will support will either be Linux or the Web. We're trying to figure that out. But the plan fully with Rust is to compile our Rust code base to web assembly, and then to port our Metal shaders to WebGL and do the rendering that way. I actually think there's interesting Terminal use cases for a browser, the most interesting ones are if you're working against a session that is hosted in the cloud some place, you really maybe don't need a desktop app for it. And if you want to work in a way that's more collaborative, I think it's really cool to have the option to sort of collaborate by sharing links and not make people install native software. We're very interested in using our Rust code base to do a browser based rendering, not so much an Electron based rendering. Because for that, we'll just be full native, but for the browser, yes.

David: And people tend to think about the terminal and the command line as something that's on Linux or MacOS, but Windows has always had a terminal as well, that they tend to call it the console. Do you think there's a difference in philosophy behind how Windows users think about interacting with the terminal, the console and Unix, or how have you approached thinking of that starting on Mac first?

Zach: It's probably not going to be the best answer, because I am a lifelong Mac user and I'm not at all an expert on Windows Console or Windows Terminal. The reason we started Mac is I would say it's primarily because I've used it a lot. The people on our team have used it the most. And then we all come from companies that are heavily reliant on Linux. And so the Mac/Unix/Linux all have very similar command line environments. I think that those are the most important ones to support in the sense that most of the internet is running some version of Linux at this point.

I heard a stat, even Microsoft's cloud is primarily moving towards Linux, and Microsoft launched the subsystem for Linux. And so the Linux command line is actually sort of becoming more ubiquitous compared to the Windows one. We do get a lot of requests around supporting Windows, which is interesting, because I think the default Windows terminal experience isn't that great. I actually don't feel comfortable sort of speaking too much to sort of the technical or even really the user facing differences in it, because I'm so not from that world.

David: And what does a multiplayer terminal look like in the future?

Michelle: Yeah, I think multiplayer has two components to it. Most people think about the realtime synchronous component. So imagine being able to jump onto a terminal together with your team for firefighting when there's an outage. But at Warp we also think about the asynchronous multiplayer experience. So being able to share environment variables within your team, or if you have a bunch of very useful commands that your team could use, you could easily share that or share workflow in something a very nice actionable read me file, or if you've configured your terminal in a beautiful way, you can share your themes and you can share the settings of how you set up your themes and your environments.

David: Where does open source come into that? Because almost every terminal application that you can download today is open source, but you are not quite there yet. How are you thinking about open sourcing your code base and using that as a way to reach developers?

Michelle: Yeah, we're definitely thinking of open sourcing it. We want to open source our UI framework, and we want to open source our terminal client code. So right now we are not ready yet, because our UI framework is still not cross platform. But we've already to open source ways for you to tweak Warp. So we've already open sourced our themes, so any developer now can contribute themes to Warp and we are probably going to open source on completion specs next.

David: Before we wrap up, I have two lightning questions for you. So Michelle, do you want to take the first one? Are there any interesting dev tools that you are playing around with at the moment?

Michelle: Our teammate Kevin has been playing with Open AI's codex, and he managed to create a prototype where you could type in our terminal, "Discard Previous Commit," and then it would return, "Get Reset Hard Hit." And there also a couple of other examples that he came up with, and that's really exciting to me because imagine not having to go to Stack Overflow through Google pretty standard common commands.

David: And Zach, what about you? Interesting tools?

Zach: We are using retool as a kind of a cool way of building some internal applications that let us do things like wait list and invite code management. I've been impressed with how easy it is to... without really writing any code, build something that's pretty useful for us.

David: And then the second question you can go first on this one Zach, what is your current tech setup? What hardware and softwares are your daily driver?

Zach: I'm on an iMac M1. And then the other notable thing that I have is I bought this mechanical keyboard that's a keychron that is extraordinarily loud and drives my fiance crazy. It makes it sound like we're in a 1950s office and I'm using a typewriter to enter things into the terminal.

David: And Michelle, how about you?

Michelle: I'm using CLion and Warp as my daily driver, and my keyboard is the K860 Ergo from Logitech. It's curved, but not separate. And I have one in the office as well. And my coworkers there roast me every day because it's unusable to them.

David: Excellent. Well that's all we've got time for today. Where can people find you online, Michelle?


David: And Zach?

Zach: Zach I'll say And then we're also on twitter, @warpdotdev also spelled out. So W A R P D O T D E V. We have a discord where people are interested in what we're doing. They should go to our website and click on the community and join us.

David: Excellent. Well, thanks both for joining The Console Podcast.

Zach: Thank you so much for having us.

Michelle: Thank you, David.

David: Thanks for listening to the Console Dev Tools Podcast. Please let us know what you think on Twitter. I'm @davidmytton and you can follow Don't forget to subscribe and rate us in your podcast player. And if you are playing around with or building any interesting dev tools, please get in touch. Our emails in the show notes. See you next time.

David Mytton
About the author

David Mytton is Co-founder & CEO of Console. In 2009, he founded and was CEO of Server Density, a SaaS cloud monitoring startup acquired in 2018 by edge compute and cyber security company, StackPath. He is also researching sustainable computing in the Department of Engineering Science at the University of Oxford, and has been a developer for 15+ years.

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