path: root/2024/captions/emacsconf-2024-shell--emacs-as-a-shell--christopher-howard--main.vtt

WEBVTT captioned by mark

NOTE Introduction

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Welcome to Emacs as a Shell, a talk by Christopher Howard for

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Emacs Conference 2024.

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In this talk, I would like to explore, or advocate for, a

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particular perspective. I want to encourage people to

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think of Emacs not as simply an editor or a development

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environment, but rather as a shell, or at least something

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that allows us to do most of the things that we might

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otherwise want to do from a shell.

NOTE What do I mean by shell?

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What do I mean by shell? By

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shell, I mean basically an interface that allows us to

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interact with the rest of our system by entering commands.

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That definition is, perhaps, a little too broad, and so I

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will try to narrow it down with a list of features that,

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historically, we have come to expect from a shell. The Bash

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shell is one very portable and well-known shell, and for

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many of us it is maybe the prototypical example. But in the

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past there have been many other shells, and there are other

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shells available today. If we are willing to be flexible in

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our thinking, we can think of Emacs as being a shell, or at

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least providing most of the functionality that we expect

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from a shell.

NOTE What I do not mean

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Before further expanding on this idea, I must emphasize

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what I do not mean. First of all, I am not talking about

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running Bash, or some other external shell, from within

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Emacs, although this is certainly possible. I am arguing,

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rather, for using Emacs as a shell, instead of other shells.

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Second, I do not mean running a terminal emulator from

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within Emacs. Emacs has a built-in terminal emulator, but

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this is not what I mean. A terminal emulator is essentially a

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program designed to control the cursor and text appearance

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in response to various control codes in order to mimic a

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terminal display device. There are certainly legitimate

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reasons to do this. Nevertheless, in general, it does not

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make much sense to run a terminal emulator within Emacs,

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because Emacs has its own commands for controlling the

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cursor and text appearance. Also, due to the way Emacs was

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designed historically, Emacs itself believes that it is

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running on a terminal. So you end up with layers upon layers

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of terminal emulation. Anyhow, at the end of the day, Emacs

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will not perform as well as a dedicated terminal emulator

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program. I also think that, as we try to force ANSI terminal

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emulation into our Emacs workflow, this ultimately will be

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a hindrance to us in taking advantage of the natural and

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pleasant interfaces that are already available to us

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within Emacs. In brief, if your goal is simply to figure out

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how to be able to do all your normal Bash command line

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wizardry from within an Emacs window instead of a GNOME

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console window, you are headed down a different set of train

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tracks than I am. Also, something which I fear may confuse

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the issue for some viewers is the fact that Emacs ships with

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its own unique built-in shell, called the Emacs shell, or

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Eshell.

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Eshell aims to be a legitimate shell, and provides a very

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similar experience to other shells like Bash, while being

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well integrated into the Emacs interface, and without

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giving up the power of the Emacs Lisp engine. Eshell will be

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mentioned multiple times in this talk. The entire talk

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could, in fact, be about Eshell, except that I want the talk

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to cover all aspects of Emacs shell-like functionality

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through its other tools, such as interactive commands and

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special modes. So, hopefully we can keep distinct in our

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mind the ideas of Emacs as a shell versus the Emacs shell,

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though the latter is an important part of the former.

NOTE What is a shell?

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Let's get back to the fundamental idea of what is a shell. In

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the broadest definition, a shell is an interface which

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allows you to interact with your operating system through

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commands. However, from a historical perspective, there

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are a few basic capabilities which we expect to be part of

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every shell.

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First of all, the shell provides a means of launching

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external programs. Some internal or built-in commands

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might also be made available. Second, the shell provides a

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means of managing environment variables. In the past,

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environment variables often played a critical role as a

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means of passing in options, file names, device names, and

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suchlike to external programs. This is not quite as common

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today, but the environment still plays a critical role in

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managing things such as the path to executables and

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libraries, as well as various other user, desktop, and

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system settings. The shell modifies the environment and

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passes it on to external programs.

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Historically, job control was expected to be either a

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function of the shell, or easily accessible from it.

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Usually today, our personal computing is not

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batch-oriented. But typically, shells can run multiple

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processes simultaneously, as well as provide means to

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suspend and terminate processes, which are useful

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features. Shells should be able to redirect and pipeline

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process input and output. This allows the user to connect

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process input and output with files, devices, or other

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processes. Finally, shells are expected to have some

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limited scripting capability, such as the

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POSIX-compliant set of program statements and

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conditionals that Bash provides.

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As command-line wizards, there are a number of tasks we

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expect to be able to do quickly and easily from our shell,

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even though these tasks are not the domain of the shell

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itself. A common task is file management and navigation. We

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quickly navigate and manipulate the file system with

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standard utilities that do things like change the current

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working directory, rename files, move files, and delete

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files. We usually expect to have access to some additional

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process management utilities. These allow us to do things

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such as find out the status of all processes running on the

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system, and send signals to processes. Finally, we expect

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to have access to some basic networking utilities. For

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example, we should be able to run commands that set up

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network interfaces, ping computers, and download files.

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With a little reflection, we can see that Emacs can provide

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all or nearly all of the functionality we have described so

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far. And the functionality can be called conveniently

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through one of several methods.

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Either a normal interactive call, like M-x something, or a

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call to an elisp function,

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or through Eshell commands, or through some special buffer

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mode, such as the directory editor, which provides its own

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interface to some functionality.

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It may be going too far to say that Emacs is a full replacement

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for shells like Bash. Nevertheless, we can see that Emacs

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can do most of the things that we might otherwise do with our

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shell.

NOTE Launching external processes

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Let us give some examples. First, can Emacs launch

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external commands? Of course. Now, there are something

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like a half-dozen different ways to do that within Emacs, and

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some are more convenient than others. From any Elisp

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program, we can call functions like make-process and

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call-process to launch external processes.

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These, however, generally are not convenient for quick,

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one-off commands. Another option would be to run Eshell,

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which would allow us to call the external program from a

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familiar command line prompt.

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If we do not actually want to drop into Eshell just to run one

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command, we also have the interactive command,

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eshell-command,

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which would allow us to call the external program from a

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familiar command line prompt.

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If we do not actually want to drop an

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Eshell just to run one command, as I just mentioned, we also

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have the interactive command eshell-command, which allows

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us to enter in a one-off command and run that immediately.

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And finally, there is also an interactive command called

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simply shell-command.

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Shell command is like Eshell command, but instead passes

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the command off to our system shell, for example, bash.

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This is cheating, of course, but it might be useful or convenient

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in some scenarios.

NOTE Environment variables

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Regarding environment variables, Emacs can read and

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manipulate the environment variables, which in turn get

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passed on to processes which it launches. The

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general-purpose interactive commands for this are

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getenv and setenv. These commands

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deal with the one environment that is available throughout

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all parts of your running Emacs session. In other words,

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these functions deal with a global environment, which is

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the same wherever you are running getenv or

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setenv.

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An important exception is that every instance of Eshell

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maintains a distinct environment that will not be affected

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by setenv calls run in other buffers. Also, Eshell

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has some additional syntax for dealing with its

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environment, including the set and export syntax.

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Regarding job control and process management, Emacs does

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not provide job control in the way that Bash users are used

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to. We can, however, launch asynchronous processes, and do

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various things to them. From Eshell, or an eshell-command

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call, we can append the ampersand symbol to the command, and

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this will cause the process to run asynchronously in a

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dedicated buffer.

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Now, if the command is launched from Eshell, it will not

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actually run in a separate buffer, but the output will go to

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the Eshell buffer.

NOTE Processes

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We can run the interactive command list-processes to see

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all the processes running for our current Emacs session.

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In Eshell, we can run the command "jobs" to get the same list.

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This will show the process name, process buffer name,

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process ID, and some other information. We can select the

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process buffer in the process list to bring up that process

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buffer.

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We can also use the interactive command signal-process to

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send any signal to a process, including "stop" to suspend the

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process, "continue" to resume the process, and "interrupt" or

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kill to terminate the process.

NOTE Redirecting and pipelining input and output

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Regarding redirecting and pipelining input and output,

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Eshell does support redirection similar to Bash, so you can

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overwrite and append to files and some other objects. Input

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redirection is not yet implemented, but it is on the Eshell

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to-do list. Eshell also has pipes. The default pipe, which

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uses the familiar vertical bar symbol, pipes the data

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between the commands using an intermediate Emacs buffer.

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This, while usually quite practical, is less efficient

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than the system pipe. Therefore, Eshell also makes

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available a star-modified version, which uses the system

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pipe through a call to your system shell.

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So we can do things like

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direct output to a file.

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We're unfortunately not able to do input redirection, but

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we can use pipes.

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Elisp can manipulate and tie together processes in various

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ways, such as process filters and pipe processes, but I

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won't attempt to cover that. I feel like you should mention

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again that we have two kinds of pipes here available. So this

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pipe, the standard one, will pipe the data through Emacs

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buffers. That's very practical in most cases, but it is less

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efficient than piping through the system pipe. So Eshell

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makes available another symbol for that, star, vertical

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bar, that allows you to explicitly use the system pipe.

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Regarding scripting: Of course, using Emacs makes

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available all the power of the Elisp API and third-party

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packages, so we have that out of the gate. Eshell also has

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control flow statements, like an "if" construct and a "for"

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construct. See the Eshell info manual, section 3.7, for

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more details.

NOTE Scripts

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And if you wish to write a script entirely in Eshell syntax,

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and store it in a separate file, this is possible with recent

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versions of Emacs.

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Here's an example of a brief script that I wrote.

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Unfortunately, an eshell mode for proper syntax

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highlighting is not yet available, but hopefully that will

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be forthcoming. Note that Eshell syntax allows elisp

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forms to be interspersed with regular command form for

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additional scripting power. We will discuss this a little

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more later.

NOTE File system management

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Regarding file system management. In Emacs, many of the

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common file system operations are available as

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interactive commands. For example, M-x cd, to change your

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buffer's current working directory, and other M-x commands

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such as make-directory

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chmod,

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and delete-file. Of course, you can also drop into Eshell,

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or use M-x eshell-command to run the usual external commands

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for file system manipulation. Also, a file manager is built

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into Emacs, which can be run by calling M-x dired.

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The directory editor is powerful, but it is a bit strange to

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folks expecting something like Midnight Commander or the

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GNOME file manager. It gives us a number of helpful features

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like the ability to mark files, and to run elisp functions on

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them, and some other interesting ways to manipulate and

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rename the files. However, third-party Emacs extensions

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such as Midnight Commander Mode and Sunrise Commander are

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available to provide a Midnight Commander experience, for those who

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prefer that sort of file management.

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Emacs also has the nifty TRAMP functionality built in,

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which allows you, most of the time, to easily edit files on

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other computers, as well as manipulate the file system.

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This transparently works through SSH and some other

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protocols that you can specify.

NOTE Networking

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Regarding networking features, I don't have a lot of

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interesting things to say about this at the present, so I'll

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skip through this quickly. But if you do a little research,

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you will see that Emacs has a lot of functionality relating

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to making network connections, interacting with the web,

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and such like, both built-in and in available packages, as

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well as modes for doing things like Web browsing and Gemini

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browsing. And of course, you can run the usual standard

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networking commands for your system through Eshell.

NOTE A brief tour of Eshell

00:24:30.120 --> 00:24:33.759
So having put forward the main arguments for this talk, I

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would like to take some time now to give a brief tour of a few of

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the features of Eshell, the Emacs shell. It bears

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emphasizing that Eshell is not a drop-in replacement for

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Bash, or even a Bash clone, though I believe the developers

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are trying to make much of the syntax very similar. Also,

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Eshell is not a terminal emulator, and it will not display

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correctly applications which use advanced ANSI control

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codes. However, Eshell can be configured to be aware of such

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applications, and to run them automatically within the

00:25:13.301 --> 00:25:19.940
Emacs terminal emulator when launched. See section 5.1 of

00:25:19.941 --> 00:25:24.100
the Eshell manual titled Visual Commands.

00:25:32.540 --> 00:25:36.759
Though Eshell is not Bash, it has multiple features,

00:25:36.760 --> 00:25:40.679
pertaining mainly to its by-design Emacs integration,

00:25:40.680 --> 00:25:44.639
which may make it more appealing to use than Bash or another

00:25:44.640 --> 00:25:45.359
shell.

00:25:48.160 --> 00:25:52.039
For one, Eshell allows entering commands on the command

00:25:52.040 --> 00:25:55.960
line that are space and new line separated, without

00:25:55.961 --> 00:26:01.280
parentheses. Of course, all the other shells do this. But

00:26:01.281 --> 00:26:06.280
within Eshell, it is possible to enter internal Emacs

00:26:06.281 --> 00:26:11.060
functions, as well as external commands.

00:26:13.240 --> 00:26:45.739
This allows us to do things like this.

00:26:45.740 --> 00:26:49.759
As far as I understand, it is possible to enter any Emacs

00:26:49.760 --> 00:26:53.959
function on the Eshell command line. However, some special

00:26:53.960 --> 00:26:58.399
syntax may be required if you are trying to pass in something

00:26:58.400 --> 00:27:00.799
that is not a string or a number.

00:27:04.380 --> 00:27:07.919
As you might have noticed in the last example, Eshell makes

00:27:07.920 --> 00:27:12.919
it possible to use an Emacs buffer as a sink for output. It

00:27:12.920 --> 00:27:18.039
also allows using a buffer as a source of input, though this

00:27:18.040 --> 00:27:21.839
is slightly more complicated, since the buffer must be

00:27:21.840 --> 00:27:27.199
converted to a string first. I have distilled this down into

00:27:27.200 --> 00:27:30.279
my own function, named with the "at" symbol.

00:27:36.640 --> 00:27:40.319
And I will provide the brief snippet of code for this later.

00:27:54.640 --> 00:28:02.499
So to give an example, here's our messages buffer.

00:28:02.500 --> 00:28:05.399
And from Eshell, we can do something like this.

00:28:29.780 --> 00:28:34.439
Let's say here we wanted to grab our messages buffer to see

00:28:34.440 --> 00:28:38.079
everything that we had been loading during the startup

00:28:38.080 --> 00:28:38.959
process.

00:28:48.060 --> 00:28:51.879
So you can see how that could be very handy in a number of

00:28:51.880 --> 00:28:52.959
scenarios.

00:28:55.060 --> 00:29:00.239
I wanted to briefly mention that we have a helpful function

00:29:00.240 --> 00:29:03.439
here called eshell-insert-buffer-name,

00:29:11.120 --> 00:29:15.359
which allows us to insert a buffer name into the current

00:29:15.360 --> 00:29:18.439
buffer at point using completion,

00:29:24.680 --> 00:29:32.879
which can save you a lot of typing.

00:29:32.880 --> 00:29:34.799
Another nice feature of Eshell

00:29:37.220 --> 00:29:41.199
is that it allows integrating ELisp into the command line

00:29:41.200 --> 00:29:48.879
call. Let's give another example. Say we wanted to echo the

00:29:48.880 --> 00:29:53.919
date to an event file or an event log.

00:29:56.720 --> 00:30:01.639
I should probably take a moment to explain this asterisk

00:30:01.640 --> 00:30:06.999
that I'm occasionally using. So since Emacs, or excuse me,

00:30:07.000 --> 00:30:11.719
since Eshell can use internal or external Emacs, excuse me,

00:30:11.720 --> 00:30:16.999
internal Emacs commands or external commands, it may

00:30:17.000 --> 00:30:21.679
sometimes be necessary to clarify which one you want to use,

00:30:22.380 --> 00:30:27.079
since the names may overlap. Since my Eshell is configured

00:30:27.080 --> 00:30:32.319
by default to prefer the internal Emacs functions, then

00:30:32.320 --> 00:30:37.799
sometimes I have to use the asterisk to specify that I want

00:30:37.800 --> 00:30:39.079
the external version.

00:30:42.680 --> 00:31:02.639
Here I can insert a bit of Elisp,

00:31:03.180 --> 00:31:06.119
and then redirect the output to the event log.

00:31:18.720 --> 00:31:22.639
Last, I want to mention that there are some optional Eshell

00:31:22.640 --> 00:31:27.159
modules in Emacs, not turned on by default, which provide

00:31:27.160 --> 00:31:29.039
additional nifty features.

00:31:40.540 --> 00:31:45.639
On my system, I have most of the optional modules turned on.

00:31:58.320 --> 00:32:03.199
An interesting module is eshell-smart, which does various

00:32:03.200 --> 00:32:07.319
things with cursor positioning and scrolling, so as to make

00:32:07.320 --> 00:32:10.399
editing commands and reviewing output easier.

00:32:18.340 --> 00:32:23.619
Let's say I was to change directory to my boot directory

00:32:30.880 --> 00:32:35.039
and use a command which involves lots of output.

00:32:39.900 --> 00:32:44.359
You'll notice right away that the cursor positioning is set

00:32:44.360 --> 00:32:48.719
such that I'm immediately able to view the top of the output.

00:32:48.720 --> 00:32:52.879
Also, I'm able to use the space bar to page through the

00:32:52.880 --> 00:32:56.079
output.

00:32:56.080 --> 00:33:01.919
So this is an opinionated feature, which assumes that

00:33:01.920 --> 00:33:05.399
you're likely going to want to review the output

00:33:05.400 --> 00:33:10.559
immediately, or that you often will. Of course, you can

00:33:10.560 --> 00:33:17.599
always jump to the end.

00:33:19.980 --> 00:33:23.919
Also, after a command is entered, the cursor is immediately

00:33:23.920 --> 00:33:28.279
repositioned to make it easy to edit the command.

00:33:53.020 --> 00:33:56.519
And also, if I don't want to edit the command, and I do not want

00:33:56.520 --> 00:33:59.679
to review the output, I can simply start typing another

00:33:59.680 --> 00:34:00.359
command.

00:34:11.260 --> 00:34:15.519
So that covers the brief tour of Eshell features.

00:34:17.760 --> 00:34:21.127
And that basically ends my talk.

NOTE Login shell

00:34:21.128 --> 00:34:22.380
However, a handful of

00:34:22.381 --> 00:34:28.719
viewers might be wondering, is it possible to set Emacs to be

00:34:28.720 --> 00:34:37.639
my login shell to completely replace bash in your login

00:34:37.640 --> 00:34:43.719
experience? The answer is yes, but in practice there are

00:34:43.720 --> 00:34:47.399
various difficulties involved which might make it not

00:34:47.400 --> 00:34:48.359
worth the trouble.

00:35:00.440 --> 00:35:03.479
Before doing this, you'll have to answer a few initial

00:35:03.480 --> 00:35:09.519
questions. Do you want to make a new Emacs instance every

00:35:09.520 --> 00:35:13.759
time you log in, or do you want it to connect to an Emacs

00:35:13.760 --> 00:35:20.599
server? Which is popular among Emacs users, to reuse the

00:35:20.600 --> 00:35:26.599
session, or to connect to the existing session. Also, do you

00:35:26.600 --> 00:35:30.639
want a different result, whether in graphical or a terminal

00:35:30.640 --> 00:35:34.679
environment? And are you okay with your initialization

00:35:34.680 --> 00:35:39.559
file being run every time you log in, including every new tab

00:35:39.560 --> 00:35:44.520
you open in a terminal emulator? If we assume that you are

00:35:44.521 --> 00:35:50.339
using a system with /etc/passwd user management, you get

00:35:50.340 --> 00:35:53.999
one field to specify the name of the shell program that you

00:35:54.000 --> 00:35:58.479
want to use, and no arguments are allowed. So maybe you can

00:35:58.480 --> 00:36:02.679
see how this might be challenging, depending on your

00:36:02.680 --> 00:36:06.879
answers to the previous questions. You can work around

00:36:06.880 --> 00:36:10.479
these issues in various ways, like modifying the

00:36:10.480 --> 00:36:15.439
authentication system, or by specifying a script for your

00:36:15.440 --> 00:36:21.799
login shell. But if your normal workflow is to simply log in

00:36:21.800 --> 00:36:25.679
and start Emacs and run that Emacs session until your next

00:36:25.680 --> 00:36:36.979
reboot, then it probably isn't worth the bother.

NOTE Resources

00:36:36.980 --> 00:36:41.999
So thank you for listening to my talk, Emacs as a Shell, by

00:36:42.000 --> 00:36:46.319
Christopher Howard for Emacs Conference 2024.

00:36:46.860 --> 00:36:51.519
At the bottom of this page, you can see a link to the

00:36:51.520 --> 00:36:56.919
repository containing the brief amount of code that was

00:36:56.920 --> 00:37:03.679
featured here in this video, as well as a link to my personal

00:37:03.680 --> 00:37:10.279
Gemini gemlog, as well as to a Web portal version of that.

00:37:10.280 --> 00:37:13.000
Thank you.