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Eshell is a command shell implemented entirely in Emacs Lisp. It invokes no external processes beyond those requested by the user. It is intended to be a functional replacement for command shells such as bash, zsh, rc, 4dos; since Emacs itself is capable of handling most of the tasks accomplished by such tools.

Despite the sheer fact that running an Emacs shell can be fun, here are a few of the unique features offered by Eshell. More are documented in greater detail under EshellFeatures.

For those who might be using an older version of Eshell, version 2.1 represents an entirely new, module-based architecture. It supports most of the features offered by modern shells. Here is a brief list of some of its more visible features:

Eshell was designed to run on Emacs 20.4 or higher, and XEmacs 21.1 or higher. It was tested on GNU/Linux, Windows NT 4.0, and Windows 2000.

If you try to run Eshell on other versions of Emacs, here are some common problems you may run into, and how to overcome them:

Emacs 20.3: Pcomplete fails to byte compile. Instead of typing ``make install'' in the Pcomplete directory, type: ``make pcmpl-auto.el install_el''. Then, copy the file ``pcmpl-auto.el'' into the directory that pcomplete was just installed into. Why this is failing is a mystery to me. It appears that byte-compiling pcomplete from a running Emacs session works just fine.

The latest version of Eshell is 2.4.2. It can be downloaded in several forms:

Eshell is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Eshell; see the file COPYING. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

To start using Eshell, add the following to your .emacs file:

(load "eshell-auto")

This will define all of the necessary autoloads.

Now type M-x eshell. See the INSTALL file for full installation instructions.

A shell is a layer which metaphorically surrounds the kernel, or heart of an operating system. This kernel can be seen as an engine of pure functionality, waiting to serve, while the user programs take advantage of that functionality to accomplish their purpose.

The shell's role is to make that functionality accessible to the user in an unformed state. Very roughly, it associates kernel functionality with textual commands, allowing the user to interact with the operating system via linguistic constructs. Process invocation is perhaps the most significant form this takes, using the kernel's fork and exec functions.

Other programs also interact with the functionality of the kernel, but these user applications typically offer a specific range of functionality, and thus are not classed as ``shells'' proper. (What they lose in quiddity, they gain in rigidity).

Emacs is also a user application, but it does make the functionality of the kernel accessible through an interpreted language — namely, Lisp. For that reason, there is little preventing Emacs from serving the same role as a modern shell. It too can manipulate the kernel in an unpredetermined way to cause system changes. All it's missing is the shell-ish linguistic model.

Enter Eshell. Eshell translates ``shell-like'' syntax into Lisp in order to exercise the kernel in the same manner as typical system shells. There is a fundamental difference here, however, although it may seem subtle at first...

Shells like csh and Bourne shell were written several decades ago, in different times, under more restrictive circumstances. This confined perspective shows itself in the paradigm used by nearly all command-line shells since. They are linear in conception, byte stream-based, sequential, and confined to movement within a single host machine.

Emacs, on the other hand, is more than just a limited translator that can invoke subprocesses and redirect file handles. It also manages character buffers, windowing frames, network connections, registers, bookmarks, processes, etc. In other words, it's a very multi-dimensional environment, within which eshell emulates a highly linear methodology.

Taking a moment, let's look at how this could affect the future of a shell allowed to develop in such a wider field of play:

This presents a brief idea of what the fuller dimensionality of an Emacs shell could offer. It's not just the language of a shell that determines how it's used, but also the Weltanschauung underlying its design — and which is felt behind even the smallest feature. I would hope the freedom provided by using Emacs as a parent environment will invite rich ideas from others. It certainly feels as though all I've done so far is to tie down the horse, so to speak, so that he will run at a man's pace.

The author of Eshell has been a long-time user of the following shells, all of which contributed to Eshell's design: