Eshell
******

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

This manual is for Eshell, the Emacs shell.

Copyright © 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being ``A GNU Manual'', and with the Back-Cover Texts as in (a) below.  A copy of the license is included in the section entitled ``GNU Free Documentation License''.

     (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and modify this GNU manual.  Buying copies from the FSF supports it in developing GNU and promoting software freedom.''

What is Eshell?
***************

Eshell is a command shell written in Emacs Lisp.  Everything it does, it uses Emacs' facilities to do.  This means that Eshell is as portable as Emacs itself.  It also means that cooperation with Lisp code is natural and seamless.

What is a command shell?  To properly understand the role of a shell, it's necessary to visualize what a computer does for you.  Basically, a computer is a tool; in order to use that tool, you must tell it what to do---or give it ``commands.''  These commands take many forms, such as clicking with a mouse on certain parts of the screen.  But that is only one form of command input.

By far the most versatile way to express what you want the computer to do is by using an abbreviated language called script.  In script, instead of telling the computer, ``list my files, please'', one writes a standard abbreviated command word---ls.  Typing ls in a command shell is a script way of telling the computer to list your files. (This is comparable to viewing the contents of a folder using a graphical display.)

The real flexibility of this approach is apparent only when you realize that there are many, many different ways to list files.  Perhaps you want them sorted by name, sorted by date, in reverse order, or grouped by type.  Most graphical browsers have simple ways to express this.  But what about showing only a few files, or only files that meet a certain criteria?  In very complex and specific situations, the request becomes too difficult to express using a mouse or pointing device.  It is just these kinds of requests that are easily solved using a command shell.

For example, what if you want to list every Word file on your hard drive, larger than 100 kilobytes in size, and which hasn't been looked at in over six months?  That is a good candidate list for deletion, when you go to clean up your hard drive.  But have you ever tried asking your computer for such a list?  There is no way to do it!  At least, not without using a command shell.

The role of a command shell is to give you more control over what your computer does for you.  Not everyone needs this amount of control, and it does come at a cost: Learning the necessary script commands to express what you want done.  A complicated query, such as the example above, takes time to learn.  But if you find yourself using your computer frequently enough, it is more than worthwhile in the long run. Any tool you use often deserves the time spent learning to master it. (For the understandably curious, here is what that command looks like: But don't let it fool you; once you know what's going on, it's easier than it looks: ls -lt **/*.doc(Lk+50aM+5).)

Contributors to Eshell
======================

Contributions to Eshell are welcome.  I have limited time to work on this project, but I will gladly add any code you contribute to me to this package.

The following persons have made contributions to Eshell.

  * Eli Zaretskii made it possible for Eshell to run without requiring asynchronous subprocess support.  This is important for MS-DOS, which does not have such support.

  * Miles Bader contributed many fixes during the port to Emacs 21.

  * Stefan Monnier fixed the things which bothered him, which of course made things better for all.

  * Gerd Moellmann also helped to contribute bug fixes during the initial integration with Emacs 21.

  * Alex Schroeder contributed code for interactively querying the user before overwriting files.

  * Sudish Joseph helped with some XEmacs compatibility issues.

Apart from these, a lot of people have sent suggestions, ideas, requests, bug reports and encouragement.  Thanks a lot!  Without you there would be no new releases of Eshell.

Basic overview
**************

A command shell is a means of entering verbally-formed commands.  This is really all that it does, and every feature described in this manual is a means to that end.  Therefore, it's important to take firm hold on exactly what a command is, and how it fits in the overall picture of things.

Commands verbs
==============

Commands are expressed using script, a special shorthand language computers can understand with no trouble.  Script is an extremely simple language; oddly enough, this is what makes it look so complicated! Whereas normal languages use a variety of embellishments, the form of a script command is always:

     VERB [ARGUMENTS]

The verb expresses what you want your computer to do.  There are a fixed number of verbs, although this number is usually quite large.  On the author's computer, it reaches almost 1400 in number.  But of course, only a handful of these are really necessary.

Sometimes, the verb is all that's written.  A verb is always a single word, usually related to the task it performs.  reboot is a good example.  Entering that on GNU/Linux will reboot the computer---assuming you have sufficient privileges.

Other verbs require more information.  These are usually very capable verbs, and must be told specifically what to do.  The extra information is given in the form of arguments.  For example, the echo verb prints back whatever arguments you type.  It requires these arguments to know what to echo.  A proper use of echo looks like this:

     echo This is an example of using echo!

This script command causes the computer to echo back: ``This is an example of using echo!''

Although command verbs are always simple words, like reboot or echo, arguments may have a wide variety of forms.  There are textual arguments, numerical arguments---even Lisp arguments. Distinguishing these different types of arguments requires special typing, for the computer to know exactly what you mean.

Command arguments
=================

Eshell recognizes several different kinds of command arguments:

 1. Strings (also called textual arguments)

 2. Numbers (floating point or integer)

 3. Lisp lists

 4. Lisp symbols

 5. Emacs buffers

 6. Emacs process handles

Most users need to worry only about the first two.  The third, Lisp lists, occur very frequently, but almost always behind the scenes.

Strings are the most common type of argument, and consist of nearly any character.  Special characters---those used by Eshell specifically---must be preceded by a backslash (\).  When in doubt, it is safe to add backslashes anywhere and everywhere.

Here is a more complicated echo example:

     echo A\ Multi-word\ Argument\ With\ A\ \$\ dollar

Beyond this, things get a bit more complicated.  While not beyond the reach of someone wishing to learn, it is definitely beyond the scope of this manual to present it all in a simplistic manner.  Get comfortable with Eshell as a basic command invocation tool, and learn more about the commands on your system; then come back when it all sits more familiarly on your mind.  Have fun!

Commands
********

Essentially, a command shell is all about invoking commands---and everything that entails.  So understanding how Eshell invokes commands is the key to comprehending how it all works.

Invocation
==========

Unlike regular system shells, Eshell never invokes kernel functions directly, such as exec(3).  Instead, it uses the Lisp functions available in the Emacs Lisp library.  It does this by transforming the command you specify into a callable Lisp form. (To see the Lisp form that will be invoked, type: eshell-parse-command "echo hello")

This transformation, from the string of text typed at the command prompt, to the ultimate invocation of either a Lisp function or external command, follows these steps:

 1. Parse the command string into separate arguments.

Completion
==========

Aliases
=======

History
=======

Eshell knows a few built-in variables:

$+
     This variable always contains the current working directory.

$-
     This variable always contains the previous working directory (the current working directory from before the last cd command).

$_
     It refers to the last argument of the last command.

$$
     This is the result of the last command.  In case of an external command, it is t or nil.

$?
     This variable contains the exit code of the last command (0 or 1 for Lisp functions, based on successful completion).

Scripts
=======

Built-in commands
=================

Several commands are built-in in Eshell.  In order to call the external variant of a built-in command foo, you could call *foo.  Usually, this should not be necessary.  You can check what will be applied by the which command:

     ~ $ which ls
     eshell/ls is a compiled Lisp function in `em-ls.el'
     ~ $ which *ls
     /bin/ls

Some of the built-in commands have a special behaviour in Eshell:

cd
     This command changes the current working directory.  Usually, it is invoked as cd foo where foo is the new working directory.  But cd knows about a few special arguments:

     When it receives no argument at all, it changes to the home directory.

     Giving the command cd - changes back to the previous working directory (this is the same as cd $-).

     The command cd = shows the directory stack.  Each line is numbered.

     With cd =foo, Eshell searches the directory stack for a directory matching the regular expression foo and changes to that directory.

     With cd -42, you can access the directory stack by number.

history
     The history command shows all commands kept in the history ring as numbered list.  If the history ring contains eshell-history-size commands, those numbers change after every command invocation, therefore the history command shall be applied before using the expansion mechanism with history numbers.

     The n-th entry of the history ring can be applied with the !n command.  If n is negative, the entry is counted from the end of the history ring.

     !foo expands to the last command beginning with foo, and !?foo to the last command containing foo.  The n-th argument of the last command beginning with foo is accessible by !foo:n.

su
sudo
     su and sudo work as expected: they apply the following commands (su), or the command being an argument (sudo) under the permissions of somebody else.

     This does not work only on the local host, but even on a remote one, when default-directory is a remote file name.  The necessary proxy configuration of Tramp is performed automatically, Multi-hops (tramp). Example:

          ~ $ cd /ssh:otherhost:/etc
          /ssh:user@otherhost:/etc $ sudo find-file shadow

Arguments
*********

The Parser
==========

Variables
=========

Substitution
============

Globbing
========

Predicates
==========

Input/Output
************

Process control
***************

Extension modules
*****************

Writing a module
================

Module testing
==============

Directory handling
==================

Key rebinding
=============

Smart scrolling
===============

Terminal emulation
==================

Built-in UNIX commands
======================

Extras and Goodies
******************

Bugs and ideas
**************

If you find a bug or misfeature, don't hesitate to let me know!  Send email to johnw@gnu.org.  Feature requests should also be sent there.  I prefer discussing one thing at a time.  If you find several unrelated bugs, please report them separately.

If you have ideas for improvements, or if you have written some extensions to this package, I would like to hear from you.  I hope you find this package useful!

Known problems
==============

Below is complete list of known problems with Eshell version 2.4.2, which is the version included with Emacs 22.

Documentation incomplete

Differentiate between aliases and functions

     Allow for a bash-compatible syntax, such as:

          alias arg=blah
          function arg () { blah $* }

for i in 1 2 3 { grep -q a b && *echo has it } | wc -l outputs result after prompt

     In fact, piping to a process from a looping construct doesn't work in general.  If I change the call to eshell-copy-handles in eshell-rewrite-for-command to use eshell-protect, it seems to work, but the output occurs after the prompt is displayed.  The whole structured command thing is too complicated at present.

Error with bc in eshell-test

     On some XEmacs system, the subprocess interaction test fails inexplicably, although bc works fine at the command prompt.

Eshell does not delete *Help* buffers in XEmacs 21.1.8+

     In XEmacs 21.1.8, the *Help* buffer has been renamed such that multiple instances of the *Help* buffer can exist.

Pcomplete sometimes gets stuck

     You press TAB, but no completions appear, even though the directory has matching files.  This behavior is rare.

grep python $<rpm -qa> doesn't work, but using *grep does

     This happens because the grep Lisp function returns immediately, and then the asynchronous grep process expects to examine the temporary file, which has since been deleted.

Problem with C-r repeating text

     If the text before point reads "./run", and you type C-r r u n, it will repeat the line for every character typed.

Backspace doesn't scroll back after continuing (in smart mode)

     Hitting space during a process invocation, such as make, will cause it to track the bottom of the output; but backspace no longer scrolls back.

It's not possible to fully unload-feature Eshell

Menu support was removed, but never put back

Using C-p and C-n with rebind gets into a locked state

     This happened a few times in Emacs 21, but has been unreproducible since.

If an interactive process is currently running, M-! doesn't work

Use a timer instead of sleep-for when killing child processes

Piping to a Lisp function is not supported

     Make it so that the Lisp command on the right of the pipe is repeatedly called with the input strings as arguments.  This will require changing eshell-do-pipeline to handle non-process targets.

Input redirection is not supported

     See the above entry.

Problem running less without arguments on Windows

     The result in the Eshell buffer is:

          Spawning child process: invalid argument

     Also a new less buffer was created with nothing in it... (presumably this holds the output of less).

     If less.exe is invoked from the Eshell command line, the expected output is written to the buffer.

     Note that this happens on NT-Emacs 20.6.1 on Windows 2000. The term.el package and the supplied shell both use the cmdproxy program for running shells.

Implement -r, -n and -s switches for cp

Make M-5 M-x eshell switch to ``*eshell<5>*'', creating if need be

mv DIR FILE.tar does not remove directories

     This is because the tar option --remove-files doesn't do so.  Should it be Eshell's job?

Bind standard-output and standard-error

     This would be so that if a Lisp function calls print, everything will happen as it should (albeit slowly).

When an extension module fails to load, cd / gives a Lisp error

If a globbing pattern returns one match, should it be a list?

Make sure syntax table is correct in Eshell mode

     So that M-DEL acts in a predictable manner, etc.

Allow all Eshell buffers to share the same history and list-dir

There is a problem with script commands that output to /dev/null

     If a script file, somewhere in the middle, uses > /dev/null, output from all subsequent commands is swallowed.

Split up parsing of text after $ in esh-var.el

     Make it similar to the way that esh-arg.el is structured. Then add parsing of $[?\n].

After pressing M-RET, redisplay before running the next command

Argument predicates and modifiers should work anywhere in a path

          /usr/local/src/editors/vim $ vi **/CVS(/)/Root(.)
          Invalid regexp: "Unmatched ( or \\("

     With zsh, the glob above expands to all files named Root in directories named CVS.

Typing echo ${locate locate}/bin<TAB> results in a Lisp error

     Perhaps it should interpolate all permutations, and make that the globbing result, since otherwise hitting return here will result in ``(list of filenames)/bin'', which is never valuable.  Thus, one could cat only C backup files by using ls ${identity *.c}~. In that case, having an alias command name glob for identity would be useful.

Once symbolic mode is supported for umask, implement chmod in Lisp

Create eshell-expand-file-name

     This would use a data table to transform things such as ~+, ..., etc.

Abstract em-smart.el into smart-scroll.el

     It only really needs: to be hooked onto the output filter and the pre-command hook, and to have the input-end and input-start markers. And to know whether the last output group was ``successful.''

Allow for fully persisting the state of Eshell

     This would include: variables, history, buffer, input, dir stack, etc.

Implement D as an argument predicate

     It means that files beginning with a dot should be included in the glob match.

A comma in a predicate list should mean OR

     At the moment, this is not supported.

Error if a glob doesn't expand due to a predicate

     An error should be generated only if eshell-error-if-no-glob is non-nil.

(+ RET SPC TAB does not cause indent-according-to-mode to occur

Create eshell-auto-accumulate-list

     This is a list of commands for which, if the user presses RET, the text is staged as the next Eshell command, rather than being sent to the current interactive process.

Display file and line number if an error occurs in a script

wait doesn't work with process ids at the moment

Enable the direct-to-process input code in em-term.el

Problem with repeating echo ${find /tmp}

     With smart display active, if RET is held down, after a while it can't keep up anymore and starts outputting blank lines.  It only happens if an asynchronous process is involved...

     I think the problem is that eshell-send-input is resetting the input target location, so that if the asynchronous process is not done by the time the next RET is received, the input processor thinks that the input is meant for the process; which, when smart display is enabled, will be the text of the last command line!  That is a bug in itself.

     In holding down RET while an asynchronous process is running, there will be a point in between termination of the process, and the running of eshell-post-command-hook, which would cause eshell-send-input to call eshell-copy-old-input, and then process that text as a command to be run after the process.  Perhaps there should be a way of killing pending input between the death of the process, and the post-command-hook.

Allow for a more aggressive smart display mode

     Perhaps toggled by a command, that makes each output block a smart display block.

Create more meta variables

     $!
          The reason for the failure of the last disk command, or the text of the last Lisp error.

     $=
          A special associate array, which can take references of the form $=[REGEXP].  It indexes into the directory ring.

Eshell scripts can't execute in the background

Support zsh's ``Parameter Expansion'' syntax, i.e. ${NAME:-VAL}

Write an info alias that can take arguments

     So that the user can enter info chmod, for example.

Create a mode eshell-browse

     It would treat the Eshell buffer as a outline.  Collapsing the outline hides all of the output text.  Collapsing again would show only the first command run in each directory

Allow other revisions of a file to be referenced using file{rev}

     This would be expanded by eshell-expand-file-name (see above).

Print ``You have new mail'' when the ``Mail'' icon is turned on

Implement M-| for Eshell

Implement input redirection

     If it's a Lisp function, input redirection implies xargs (in a way...).  If input redirection is added, also update the file-name-quote-list, and the delimiter list.

Allow #<WORD ARG> as a generic syntax

     With the handling of word specified by an eshell-special-alist.

In eshell-veal-using-options, allow a :complete tag

     It would be used to provide completion rules for that command.  Then the macro will automagically define the completion function.

For eshell-command-on-region, apply redirections to the result

     So that + > 'blah would cause the result of the + (using input from the current region) to be inserting into the symbol blah.

     If an external command is being invoked, the input is sent as standard input, as if a cat <region> | had been invoked.

     If a Lisp command, or an alias, is invoked, then if the line has no newline characters, it is divided by whitespace and passed as arguments to the Lisp function.  Otherwise, it is divided at the newline characters.  Thus, invoking + on a series of numbers will add them; min would display the smallest figure, etc.

Write eshell-script-mode as a minor mode

     It would provide syntax, abbrev, highlighting and indenting support like emacs-lisp-mode and shell-mode.

In the history mechanism, finish the bash-style support

     This means !n, !#, !:%, and !:1- as separate from !:1*.

Support the -n command line option for history

Implement fc in Lisp

Specifying a frame as a redirection target should imply the currently active window's buffer

Implement >FUNC-OR-FUNC-LIST

     This would allow for an ``output translators'', that take a function to modify output with, and a target.  Devise a syntax that works well with pipes, and can accommodate multiple functions (i.e., >'(upcase regexp-quote) or >'upcase).

Allow Eshell to read/write to/from standard input and output

     This would be optional, rather than always using the Eshell buffer. This would allow it to be run from the command line (perhaps).

Write a help command

     It would call subcommands with --help, or -h or /?, as appropriate.

Implement stty in Lisp

Support rc's matching operator, e.g. ~ (LIST) REGEXP

Implement bg and fg as editors of eshell-process-list

     Using bg on a process that is already in the background does nothing.  Specifying redirection targets replaces (or adds) to the list current being used.

Have jobs print only the processes for the current shell

How can Eshell learn if a background process has requested input?

Support 2>&1 and >& and 2> and |&

     The syntax table for parsing these should be customizable, such that the user could change it to use rc syntax: >[2=1].

Allow $_[-1], which would indicate the last element of the array

Make $x[*] equal to listing out the full contents of x

     Return them as a list, so that $_[*] is all the arguments of the last command.

Copy ANSI code handling from term.el into em-term.el

     Make it possible for the user to send char-by-char to the underlying process.  Ultimately, I should be able to move away from using term.el altogether, since everything but the ANSI code handling is already part of Eshell.  Then, things would work correctly on MS-Windows as well (which doesn't have /bin/sh, although term.el tries to use it).

Make the shell spawning commands be visual

     That is, make (su, bash, telnet, rlogin, rsh, etc.) be part of eshell-visual-commands.  The only exception is if the shell is being used to invoke a single command.  Then, the behavior should be based on what that command is.

Create a smart viewing command named open

     This would search for some way to open its argument (similar to opening a file in the Windows Explorer).

Alias read to be the same as open, only read-only

Write a tail command which uses view-file

     It would move point to the end of the buffer, and then turns on auto-revert mode in that buffer at frequent intervals---and a head alias which assumes an upper limit of eshell-maximum-line-length characters per line.

Make dgrep load dired, mark everything, then invoke dired-do-search

Write mesh.c

     This would run Emacs with the appropriate arguments to invoke Eshell only.  That way, it could be listed as a login shell.

Use an intangible PS2 string for multi-line input prompts

Auto-detect when a command is visual, by checking TERMCAP usage

The first keypress after M-x watson triggers `eshell-send-input'

Make / electric

     So that it automatically expands and corrects pathnames.  Or make pathname completion for Pcomplete auto-expand /u/i/std<TAB> to /usr/include/std<TAB>.

Write the pushd stack to disk along with last-dir-ring

Add options to eshell/cat which would allow it to sort and uniq

Implement wc in Lisp

     Add support for counting sentences, paragraphs, pages, etc.

Once piping is added, implement sort and uniq in Lisp

Implement touch in Lisp

Implement comm in Lisp

Implement an epatch command in Lisp

     This would call ediff-patch-file, or ediff-patch-buffer, depending on its argument.

Have an option such that ls -l generates a dired buffer

Write a version of xargs based on command rewriting

     That is, find X | xargs Y would be indicated using Y ${find X}.  Maybe eshell-do-pipelines could be changed to perform this on-thy-fly rewriting.

Write an alias for less that brings up a view-mode buffer

     Such that the user can press SPC and DEL, and then q to return to Eshell.  It would be equivalent to: X > #<buffer Y>; view-buffer #<buffer Y>.

Make eshell-mode as much a full citizen as shell-mode

     Everywhere in Emacs where shell-mode is specially noticed, add eshell-mode there.

Permit the umask to be selectively set on a cp target

Problem using M-x eshell after using eshell-command

     If the first thing that I do after entering Emacs is to run eshell-command and invoke ls, and then use M-x eshell, it doesn't display anything.

M-RET during a long command (using smart display) doesn't work

     Since it keeps the cursor up where the command was invoked.

GNU Free Documentation License
******************************

     [file doclicense.texi not included]