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emfy

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A dark and sleek Emacs setup for general purpose editing and programming

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Emacs for You (Emfy)
====================

This project provides a tiny [`init.el`] file to set up Emacs quickly.
This document provides a detailed description of how to set it up and
get started with Emacs.

[![View Source][Source SVG]][Source URL]
[![Mastodon][Mastodon SVG]][Mastodon URL]

[Source SVG]: https://img.shields.io/badge/view-init.el-brightgreen
[Source URL]: init.el
[Mastodon SVG]: https://img.shields.io/badge/mastodon-%40susam-%2355f
[Mastodon URL]: https://mastodon.social/@susam
[`init.el`]: init.el
[`em`]: em

Further this project also provides a tiny convenience command named
[`em`] to start Emacs server and edit files using Emacs server.  This
helps in using Emacs efficiently.  This script and its usage is
explained in detail later in the [Emacs Server](#emacs-server) and
[Emacs Launcher](#emacs-launcher) sections.  Here is how the Emacs
environment is going to look after setting up this project:

[![Screenshot of Emacs][demo-img]][demo-img]

[demo-img]: https://susam.github.io/blob/img/emfy/emfy-0.4.0.png

If you are already comfortable with Emacs and only want to understand
the content of [`init.el`] or [`em`], you can skip ahead directly to
the [Line-by-Line Explanation](#line-by-line-explanation) section that
describes every line of these files in detail.

Contents
--------

* [Who Is This For?](#who-is-this-for)
* [Features](#features)
* [Get Started](#get-started)
* [Step-by-Step Usage](#step-by-step-usage)
  * [Use Emacs](#use-emacs)
  * [Use Paredit](#use-paredit)
  * [Evaluate Emacs Lisp Code](#evaluate-emacs-lisp-code)
  * [Use Rainbow Delimiters](#use-rainbow-delimiters)
* [Useful Terms](#useful-terms)
* [Line-by-Line Explanation](#line-by-line-explanation)
  * [Tweak UI](#tweak-ui)
  * [Dark Theme](#dark-theme)
  * [Highlight Parentheses](#highlight-parentheses)
  * [Minibuffer Completion](#minibuffer-completion)
  * [Show Stray Whitespace](#show-stray-whitespace)
  * [Require Final Newline](#require-final-newline)
  * [Single Space for Sentence Spacing](#single-space-for-sentence-spacing)
  * [Indentation](#indentation)
  * [Keep Working Directory Tidy](#keep-working-directory-tidy)
  * [Custom Command and Key Sequences](#custom-command-and-key-sequences)
  * [Emacs Server](#emacs-server)
  * [Install Packages](#install-packages)
  * [Configure Paredit](#configure-paredit)
  * [Configure Rainbow Delimiters](#configure-rainbow-delimiters)
  * [End of File](#end-of-file)
  * [Emacs Launcher](#emacs-launcher)
* [Opinion References](#opinion-references)
* [Channels](#channels)
* [License](#license)
* [See Also](#see-also)

Who Is This For?
----------------

Are you an absolute beginner to Emacs?  Are you so new to Emacs that
you do not even have the `~/.emacs.d/` directory on your file system?
Have you come across recommendations to use starter kits like Doom
Emacs, Spacemacs, etc. but then you wondered if you could use vanilla
Emacs and customise it slowly to suit your needs without having to
sacrifice your productivity in the initial days of using Emacs?  Do
you also want your Emacs to look sleek from day zero?  If you answered
"yes" to most of these questions, then this project is for you.

The [`init.el`] file in this project provides a quick way to get
started with setting up your Emacs environment.  This document
explains how to do so in a step-by-step manner.  This document also
explains the content of [`init.el`] and [`em`] in a line-by-line
manner.

Note that many customisations in the Emacs initialisation file
available in this project are a result of the author's preferences.
They may or may not match others' preferences.  They may or may not
suit your taste and requirements.  Wherever applicable, the pros and
cons of each customisation and possible alternatives are discussed in
this document.  You are encouraged to read the line-by-line
explanation that comes later in this document, understand each
customisation, and modify the initialisation file to suit your needs.

Features
--------

This project provides a file named [`init.el`] that offers the
following features:

- Disable a few UI elements to provide a clean and minimal
    look-and-feel.
  - Show current column number in the mode line.
  - Load a dark colour theme named Wombat.
  - Customise the colour theme to accentuate the cursor, comments, and
    search matches.
  - Highlight matching parentheses.
  - Enable Fido mode for automatic completion of minibuffer input.
  - Show trailing whitespace at the end of lines clearly.
  - Show trailing newlines at the end of buffer clearly.
  - Show missing newlines at the end of buffer clearly.
  - Always add a newline automatically at the end of a file while
    saving.
  - Use single spacing convention to end sentences.
  - Use spaces, not tabs, for indentation.
  - Configure indentation settings according to popular coding
    conventions.
  - Move auto-save files and backup files to a separate directory to
    keep our working directories tidy.
  - Do not move original files while creating backups.
  - Provide examples of user-defined custom commands and a few custom
    key sequences.
  - Start Emacs server automatically, so that terminal users can use
    Emacs client to edit files with an existing instance of Emacs.
  - Custom command to install configured packages conveniently.
  - Install Markdown mode for convenient editing of Markdown files.
  - Install and configure Paredit for editing S-expressions
    efficiently.
  - Install and configure Rainbow Delimiters to colour parentheses by
    their nesting depth level.

Additionally, this project also provides a convenience command named
[`em`] that is a thin wrapper around the `emacs` and `emacsclient`
commands.  It offers the following features:

- Start a new instance of Emacs when requested.
  - Open files in an existing Emacs server if a server is running
    already.
  - Automatically start a new Emacs server if a server is not running
    already.

All of these features along with every line of code that enables these
features are explained in the sections below.

Get Started
-----------

This section helps you to set up Emfy quickly and see what the end
result looks like.  Perform the following steps to get started:

1. Install Emacs 28.1 or later.

On macOS, enter the following command if you have
    [Homebrew](https://brew.sh):

```sh
    brew install --cask emacs
    ```

On Debian, Ubuntu, or another Debian-based Linux system, enter the
    following command:

```sh
    sudo apt-get install emacs
    ```

For other environments, visit https://www.gnu.org/software/emacs/
    to see how to install Emacs.

2. Copy the Emacs initialisation file [`init.el`] provided here to
    your home directory.  Here is an example `curl` command that does
    this:

```sh
    mkdir ~/.emacs.d
    curl -L https://github.com/susam/emfy/raw/main/init.el >> ~/.emacs.d/init.el
    ```

Here is another alternative that copies the initialisation file to
    an XDG-compatible location as follows:

```sh
    mkdir -p ~/.config/emacs
    curl -L https://github.com/susam/emfy/raw/main/init.el >> ~/.config/emacs/init.el
    ```

Some Emacs users who have been using Emacs for a long time like to
    keep the initialisation file at its traditional location
    illustrated below:

```sh
    curl -L https://github.com/susam/emfy/raw/main/init.el >> ~/.emacs
    ```

Emacs can automatically load the Emacs initialisation file from
    any of the paths used above.  See section [The Emacs
    Initialisation File][emacs-init-doc] of the Emacs manual for more
    details about this.

3. Copy the Emacs launcher script [`em`] provided here to some
    directory that belongs to your `PATH` variable.  For example, here
    are a few commands that download this script and place it in the
    `/usr/local/bin/` directory:

```sh
    curl -L https://github.com/susam/emfy/raw/main/em > /tmp/em
    sudo mv /tmp/em /usr/local/bin/em
    chmod +x /usr/local/bin/em
    ```

The usefulness of this launcher script will be explained in the
    section [Emacs Launcher](#emacs-launcher) later.

4. Install packages configured in Emfy:

```sh
    emacs --eval '(progn (install-packages) (kill-emacs))'
    ```

We will see how this command works later in the section [Install
    Packages](#install-packages).

On macOS, you may receive the following error message in a dialog
    box: '“Emacs.app” can’t be opened because Apple cannot check it
    for malicious software.'  To resolve this issue, go to Apple menu >
    System Preferences > Security & Privacy > General and click "Open
    Anyway".

5. Start Emacs:

```sh
    emacs
    ```

Now that your environment is setup, read the next section to learn how
to use this environment in more detail.

[emacs-init-doc]: https://www.gnu.org/software/emacs/manual/html_node/emacs/Init-File.html

Step-by-Step Usage
------------------

### Use Emacs

Emacs is a very powerful and extensible editor.  It comes with over
10,000 built-in commands.  A small section like this can barely
scratch the surface of Emacs.  Yet, this section makes a modest
attempt at getting you started with Emacs and then provides more
resources to learn further.  Perform the following steps to get
started:

1. Start Emacs:

```sh
    emacs
    ```

2. Within Emacs, enter the following command to open a file, say,
    `hello.txt`:

```
    C-x C-f hello.txt RET
    ```

A new buffer to edit `hello.txt` is created.  If a file with that
    name already exists on your file system, then it loads the content
    of the file into the buffer.

Note that in the Emacs world (and elsewhere too), the notation
    `C-` denotes the <kbd>ctrl</kbd> modifier key.  Thus `C-x` denotes
    <kbd>ctrl</kbd>+<kbd>x</kbd>.

The notation `RET` denotes the <kbd>enter</kbd> or
    <kbd>return</kbd> key.

Typing consecutive `C-` key sequences can be optimised by pressing
    and holding down the <kbd>ctrl</kbd> key, then typing the other
    keys, and then releasing the <kbd>ctrl</kbd> key.  For example, to
    type `C-x C-f`, first press and hold down <kbd>ctrl</kbd>, then
    type <kbd>x</kbd>, then type <kbd>f</kbd>, and then release
    <kbd>ctrl</kbd>.  In other words, think of `C-x C-f` as `C-(x f)`.
    This shortcut works for other modifier keys too.

3. Now type some text into the buffer.  Type out at least 3-4 words.
    We will need it for the next two steps.

4. Move backward by one word with the following key sequence:

```
    M-b
    ```

The notation `M-` denotes the meta modifier key.  The above
    command can be typed with <kbd>alt</kbd>+<kbd>b</kbd> or
    <kbd>option</kbd>+<kbd>b</kbd> or <kbd>esc</kbd> <kbd>b</kbd>.

If you face any issue with the <kbd>alt</kbd> key or the
    <kbd>option</kbd> key, read [Emacs Wiki: Meta Key
    Problems](https://www.emacswiki.org/emacs/MetaKeyProblems).

5. Now move forward by one word with the following key sequence:

```
    M-f
    ```

5. The `C-g` key sequence cancels the current command.  This can be
    used when you mistype a command and want to start over or if you
    type a command partially, then change your mind and then you want
    to cancel the partially typed command.  Try out these examples:

```
    C-x C-f C-g
    ```

```
    C-x C-g
    ```

7. Save the buffer to a file on the file system with this command:

```
    C-x C-s
    ```

8. Quit Emacs:

```
    C-x C-c
    ```

Now you know how to start Emacs, open a file, save it, and quit.
Improve your Emacs knowledge further by taking the Emacs tutorial that
comes along with Emacs.  In Emacs, type `C-h t` to start the tutorial.

The key bindings to perform various operations like creating file,
saving file, quitting the editor, etc. may look arcane at first, but
repeated usage of the key bindings develops muscle memory soon and
after having used them for a few days, one does not even have to think
about them.  The fingers do what the mind wants effortlessly due to
muscle memory.

While you are getting used to the Emacs key bindings, keep this [GNU
Emacs Reference Card][emacs-ref] handy.  Also, if you are using it in
GUI mode, then the menu options can be quite helpful.

[emacs-ref]: https://www.gnu.org/software/emacs/refcards/pdf/refcard.pdf

### Use Paredit

Paredit helps in keeping parentheses balanced and also in performing
structured editing of S-expressions in Lisp code.  It provides a
powerful set of commands to manipulate S-expressions in various ways.
Perform the following steps to get started with Paredit:

1. Run Emacs:

```sh
    emacs
    ```

2. Open an Emacs Lisp source file:

```
    C-x C-f foo.el
    ```

3. Type the following code only:

```elisp
    (defun square (x
    ```

At this point, Paredit should have inserted the two closing
    parentheses automatically.  The code should look like this:

```elisp
    (defun square (x))
                    -
    ```

The cursor should be situated just after the parameter `x`.  The
    underbar shows where the cursor should be.

4. Type the closing parentheses now.  Yes, type it even if the
    closing parenthesis is already present.  The cursor should now
    skip over the first closing parenthesis like this:

```elisp
    (defun square (x))
                     -
    ```

Of course, there was no need to type the closing parenthesis
    because it was already present but typing it out to skip over it
    is more efficient than moving over it with movement commands.
    This is, in fact, a very nifty feature of Paredit.  We can enter
    code with the same keystrokes as we would without Paredit.

5. Now type <kbd>enter</kbd> to insert a newline just before the last
    parenthesis.  A newline is inserted like this:

```elisp
    (defun square (x)
      )
      -
    ```

6. Now type only this:

```elisp
    (* x x
    ```

Again, Paredit would insert the closing parenthesis automatically.
    The code should look like this now:

```elisp
    (defun square (x)
      (* x x))
            -
    ```

There is a lot more to Paredit than this.  To learn more, see [The
Animated Guide to Paredit][paredit-ref].

Note: While many Lisp programmers find Paredit very convenient and
powerful while manipulating S-expressions in Lisp code, there are a
few people who do not like Paredit because they find the Paredit
behaviour intrusive.  See the [Opinion References](#opinion-references)
section for more discussion on this topic.

[paredit-ref]: http://danmidwood.com/content/2014/11/21/animated-paredit.html

### Evaluate Emacs Lisp Code

The previous section shows how to write some Emacs Lisp code and how
Paredit helps in keeping the parentheses balanced.  In this section,
we will see how to execute some Emacs Lisp code.

1. Run Emacs:

```sh
    emacs
    ```

2. Open an Emacs Lisp source file:

```
    C-x C-f foo.el
    ```

3. Enter the following code:

```elisp
    (defun square (x)
      (* x x))
    ```

4. With the cursor placed right after the last closing parenthesis,
    type `C-x C-e`.  The name of the function defined should appear in
    the echo area at the bottom.  This confirms that the function has
    been defined.

5. Now add the following code to the Emacs Lisp source file:

```elisp
    (square 5)
    ```

6. Once again, with the cursor placed right after the last closing
    parenthesis, type `C-x C-e`.  The result should appear in the echo
    area at the bottom.

### Use Rainbow Delimiters

There is not much to learn about using Rainbow Delimiters.  In the
previous sections, you must have seen that as you type nested
parentheses, each parenthesis is highlighted with a different colour.
That is done by Rainbow Delimiters.  It colours each parenthesis
according to its nesting depth level.

Note: Not everyone likes Rainbow Delimiters.  Some people find
parentheses in multiple colours distracting.  See the [Opinion
References](#opinion-references) section for more discussion on this
topic.

Useful Terms
------------

In this section, we clearly describe a few terms that we use later in
this document.

- *Frame*: The Emacs manual uses the term frame to mean a GUI
    window, or a region of the desktop, or the terminal where Emacs is
    displayed.  We do not call it window in Emacs parlance because the
    term "window" is reserved for another element discussed further
    below in this list.

- *Menu bar*: An Emacs frame displays a menu bar at the very top.
    It allows access to commands via a series of menus.

- *Echo area*: An Emacs frame displays an echo area at the very
    bottom.  The echo area displays informative messages.

- *Minibuffer*: The echo area is also used to display the
    minibuffer, a special buffer where we can type and enter arguments
    to commands, such as the name of a file to be edited after typing
    the key sequence `C-x C-f`.

- *Tool bar*: On a graphical display, a tool bar is displayed
    directly below the menu bar.  The tool bar contains a row of icons
    that provides quick access to several editing commands.

- *Window*: The main area of the frame between the menu bar or the
    tool bar (if it exists) and the echo area contains one or more
    windows.  This is where we view or edit files.  Each window
    displays a *buffer*, i.e., the text or graphics we are editing or
    viewing.  By default, only one window is displayed when we start
    Emacs.  We can split this main area into multiple windows using
    key sequences like `C-x 2`, `C-x 3`, etc. and then open different
    files or buffers in different windows.

- *Mode line*: The last line of each window is a mode line.  It
    displays information about the buffer.  For example, it shows the
    name of the buffer, the line number at which the cursor is
    currently present, etc.

- *Scroll bar*: On a graphicaly display, a scroll bar is displayed
    on one side which can be used to scroll through the buffer.

There are many other peculiar terms found in the world of Emacs such
as the term *point* to refer to the current location of the cursor,
the term *kill* to cut text, the term *yank* to paste text, etc. but
we will not discuss them here for the sake of brevity.  The meanings
of most such terms become obvious from the context when you encounter
them.  The terms described above should be sufficient to understand
the line-by-line explanation presented in the next section.

Line-by-Line Explanation
------------------------

This section explains the [`init.el`] file provided here line-by-line.

### Tweak UI

The first few lines in our [`init.el`] merely tweak the Emacs user
interface.  These are of course not essential for using Emacs.
However, many new Emacs users often ask how to customise the user
interface to add a good colour scheme and make it look minimal, so
this section indulges a little in customising the user interface.

Here is a line-by-line explanation of the UI tweaks in [`init.el`]:

- When Emacs runs in a GUI window, by default, it starts with a menu
    bar, tool bar, and scroll bar.  Some users like to hide them in
    order to make the Emacs frame look clean and minimal.  The
    following lines disable the tool bar and scroll bar.  The menu bar
    is left enabled.

```elisp
    (when (display-graphic-p)
      (tool-bar-mode 0)
      (scroll-bar-mode 0))
    ```

The `when` expression checks if Emacs is running with graphic
    display before disabling the tool bar and scroll bar.  Without the
    `when` expression, we get the following error on Emacs without
    graphic display support: `Symbol's function definition is void:
    tool-bar-mode`.  An example of Emacs without graphics support is
    `emacs-nox` on Debian 10.  Note that this is only an author's
    preference.  You may comment out one or more of these lines if you
    want to retain the tool bar or scroll bar.

Some users like to hide the menu bar as well.  To disable the menu
    bar, include `(menu-bar-mode 0)` as top-level-expression (i.e.,
    outside the `when` expression) in the initialisation file.  Even
    with the menu bar disabled, the menu can be accessed anytime by
    typing `<f10>`.  For beginners to Emacs, it is advisable to keep
    the menu bar enabled because it helps in discovering new features.

- Inhibit the startup screen with the `Welcome to GNU Emacs` message
    from appearing:

```elisp
    (setq inhibit-startup-screen t)
    ```

If you are a beginner to Emacs, you might find the startup screen
    helpful.  It contains links to tutorial, manuals, common tasks,
    etc.  If you want to retain the startup screen, comment this line
    out.

- Show column number in the mode line:

```elisp
    (column-number-mode)
    ```

By default, Emacs shows only the current line number in the mode
    line.  For example, by default, Emacs may display something like
    `L4` in the mode line to indicate that the cursor is on the fourth
    line of the buffer.  The above Emacs Lisp code enables column
    number display in the mode line.  With column number enabled,
    Emacs may display something like `(4,0)` to indicate the cursor is
    at the beginning of the fourth line.

### Dark Theme

In this section, we will choose a dark theme for Emacs.  If you do not
like dark themes, you might want to stick with the default theme,
choose another theme, or skip this section.

- Load a beautiful dark colour theme known as `wombat`:

```elisp
    (load-theme 'wombat)
    ```

If you want to check the other built-in themes, type `M-x
    customize-themes RET`.  A new window with a buffer named `*Custom
    Themes*` appear.  In this buffer, select any theme you want to
    test.  After you are done testing, you can close this new window
    with `C-x 0`.

By default the Wombat theme looks like this:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-wombat1.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-wombat1.png"
        alt="Screenshot of Wombat default theme"
        width="580"></a>

In this theme, the cursor, search matches, and comments can often
    be difficult to spot because they are all coloured with different
    shades of grey while the background is also grey.  In the next few
    points, we will customise this theme a little to make these
    elements easier to spot.  We colour them differently to add more
    contrast between the background and foreground colours of these
    elements.  In the end, our customised Wombat theme would look like
    this:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-wombat2.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-wombat2.png"
        alt="Screenshot of Wombat custom theme"
        width="580"></a>

- Choose a darker shade of grey for the background colour to improve
    the contrast of the theme:

```elisp
    (with-eval-after-load 'wombat-theme
      (set-face-background 'default "#111")
    ```

The above `with-eval-after-load` expression ensures that the code
    within its body is executed after `wombat-theme` gets loaded.
    Since `wombat-theme` is already loaded here (due to the
    `load-theme` expression discussed earlier), the body is evaluated
    immediately.  However, if `wombat-theme` were not yet loaded, the
    body would be evaluated as soon as `wombat-theme` gets loaded.

The first expression in the the body sets the background colour to
    `#111`, i.e., a very dark shade of grey.

The name `wombat-theme` refers to the feature provided by the
    Wombat theme.  Emacs packages (including the ones for themes) can
    declare the feature they provide.  If we ever remove or comment
    out the `load-theme` expression mentioned earlier, then the
    `wombat-theme` feature will not be loaded and the body of the
    `with-eval-after-load` expression will not be executed.
    Therefore, removing or commenting out the `load-theme` call is a
    convenient way to disable the theme along with all the additional
    color customizations made here.

- Choose a pale shade of orange for the cursor, so that it stands
    out clearly against the dark grey background:

```elisp
      (set-face-background 'cursor "#c96")
    ```

- Use tangerine yellow to colour the comments:

```elisp
      (set-face-foreground 'font-lock-comment-face "#fc0")
    ```

- Highlight the current search match with bright yellow background
    and dark foreground:

```elisp
      (set-face-background 'isearch "#ff0")
      (set-face-foreground 'isearch "#000")
    ```

- Highlight search matches other than the current one with a darker
    shade of yellow as the background and dark foreground:

```elisp
      (set-face-background 'lazy-highlight "#990")
      (set-face-foreground 'lazy-highlight "#000"))
    ```

**Personal note:** I see that many recent colour themes choose a dim
colour for comments in code.  Such colour themes intend to
underemphasise the comments.  I think comments play an important role
in code meant to be read by humans and should be emphasised
appropriately.  That's why I have chosen tangerine yellow for
comments.  This makes the comments are easily readable.

### Line Numbers

Enable line numbers in modes for configuration, programming, and text
with the following loop:

```elisp
(dolist (hook '(prog-mode-hook conf-mode-hook text-mode-hook))
  (add-hook hook 'display-line-numbers-mode))
```

Every buffer has a *major mode* which determines the editing
behaviour, syntax highlighting, etc. of the buffer.  To see the
current major mode, type `M-: major-mode RET`.  The name of the
current major mode is also always displayed in the mode line at the
bottom.

The `add-hook` calls in the loop above ensure that
`display-line-numbers-mode` is enabled automatically when certain
major modes become active.  In particular, this ensures that line
numbers are enabled while editing configuration files, program files,
or text files.  For instance, when editing a C program (say with `C-x
C-f foo.c RET`), the above hook enables line numbers for the buffer
for the C program file.  This happens because while editing C program
files, the major mode named `c-mode` is activated and `c-mode` is
derived from `prog-mode`.

The above loop also ensures that this feature *does not* get enabled
while working with other types of buffers.  For example, if we start a
terminal emulator with `M-x ansi-term RET`, this feature does not get
enabled because the terminal emulator buffer has the major mode named
`term-mode` which is not derived from any of the three modes mentioned
above.  Displaying line numbers in such a mode can be distracting, so
we keep line numbers disabled in such modes.

### Highlight Parentheses

The following points describe how we enable highlighting of
parentheses:

- The next point shows how to enable highlighting of matching pair
    of parentheses.  By default, there is a small delay between the
    movement of a cursor and the highlighting of the matching pair of
    parentheses.  The following line of code gets rid of this delay:

```elisp
    (setq show-paren-delay 0)
    ```

This line of code must come before the one in the next point for
    it to be effective.

- Highlight matching parentheses:

```elisp
    (show-paren-mode)
    ```

A pair of parentheses is highlighted when the cursor is on the
    opening parenthesis of the pair or just after the closing
    parenthesis of the pair.

### Minibuffer Completion

Enable automatic minibuffer completion:

```elisp
(fido-vertical-mode)
```

To test this out, perform the following exercises:

- Type `C-x C-f /etc/hst` and watch Fido mode automatically
    presenting `/etc/hosts` as one of the completion options.  Type
    `RET` to select it.  Alternatively, type `C-n` and/or `C-p` to
    pick a different option and type `RET`.

- Type `C-x b msg RET` and watch Fido presenting the buffer named
    `*Messages*` as one of the options and selecting it.  By the way,
    the key sequence `C-x b` is used to switch buffers.

- Type `M-x wspmod RET` and watch Fido presenting the command named
    `whitespace-mode` as one of the options and selecting it.  The key
    sequence `M-x` is used to execute Emacs commands.  We will see
    later how to make our own commands.

In the steps above, note how it is not necessary to type out the
filename or buffer name or command accurately.  We can enter our input
partially and Fido will automatically find matches for it.

### Show Stray Whitespace

While writing text files, it can often be useful to quickly spot any
trailing whitespace at the end of lines or unnecessary trailing new
lines at the end of the file.  The next few points describe how we
highlight stray whitespace and newlines.

- Highlight trailing whitespace at the end of lines in modes for
    configuration, programming, and text with the following loop:

```elisp
    (dolist (hook '(conf-mode-hook prog-mode-hook text-mode-hook))
      (add-hook hook (lambda () (setq show-trailing-whitespace t))))
    ```

When the variable `show-trailing-whitespace` is set to `t`, any
    stray trailing whitespace at the end of lines is highlighted
    (usually with a red background) as shown in the screenshot below:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem1.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem1.png"
        alt="Screenshot of whitespace highlighted in Emacs"
        width="580"></a>

The screenshot above shows one stray trailing space in the second
    line and two trailing spaces in the third line.  These trailing
    spaces can be removed with the key sequence `M-x
    delete-trailing-whitespace RET`.

Note that we enable this feature only for modes pertaining to
    configuration, programming, and text.  It can be distracting to
    see stray whitespace highlighted in other modes like `term-mode`,
    `erc-mode`, etc.

- Show the end of buffer with a special glyph in the left fringe:

```elisp
    (setq-default indicate-empty-lines t)
    ```

Showing the end of the buffer conspicuously can be helpful to spot
    any unnecessary blank lines at the end of a buffer.  A blank line
    is one that does not contain any character except the terminating
    newline itself.  Here is a screenshot that demonstrates this
    feature:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem2.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem2.png"
        alt="Screenshot of non-existent line indicators"
        width="580"></a>

The screenshot shows that there are two blank lines just before
    the end of the buffer.  The tiny horizontal dashes on the left
    fringe mark the end of the buffer.  Note: This is similar to how
    Vim displays the tilde symbol (`~`) to show the end of the buffer.
    The trailing blank lines at the end of a buffer can be removed
    with the key sequence `M-x delete-trailing-whitespace RET`.

- Show buffer boundaries in the left fringe:

```elisp
    (setq-default indicate-buffer-boundaries 'left)
    ```

The buffer boundaries can be useful to check if the last line of
    the buffer has a terminating newline or not.  If the buffer does
    not contain a terminating newline, then a top-right corner shape
    (`⌝`) appears in the fringe.  For example, see this screenshot of
    a file that does not contain a terminating newline:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem3.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem3.png"
        alt="Screenshot of a file without terminating newline"
        width="580"></a>

If there is only one line in the buffer and that line is
    terminated with a newline then a left-bracket (`[`) appears in the
    fringe.  If there are multiple lines in the buffer and the last
    line is terminated with a newline then a bottom-left corner shape
    (`⌞`) appears in the fringe.  Here is a screenshot of a file that
    contains a terminating newline:

<a href="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem4.png"><img
        src="https://susam.github.io/blob/img/emfy/emfy-0.4.0-lorem4.png"
        alt="Screenshot of a file with terminating newline"
        width="580"></a>

To summarise, these shapes (`[`, `⌞`, or `⌝`) show where the last
    newline of the buffer exists.  The last newline of the buffer
    exists above the lower horizontal bar of these shapes.  No
    newlines exist below the lower horizontal bar.

### Require Final Newline

It is good practice to terminate text files with a newline.  For many
types of files, such as files with extensions `.c`, `.el`, `.json`,
`.lisp`, `.org`, `.py`, `.txt`, etc., Emacs inserts a terminating
newline automatically when we save the file with `C-x C-s`.  Emacs
achieves this by ensuring that the major modes for these files set the
variable `require-final-newline` to `t` by default.  However, there
are many other types of files, such as files with extensions `.ini`,
`.yaml`, etc. for which Emacs does not insert a terminating newline
automatically.  We now  ensure that Emacs always inserts a
terminating newline for all types of files with the following call:

```elisp
(setq require-final-newline t)
```

Many tools on Unix and Linux systems expect text files to be
terminated with a newline.  For example, in a crontab entry, if the
final line is not followed by a terminating newline, it is ignored.
Similarly, `wc -l` does not count the final line if it is not followed
by a terminating newline.  That is why, in the above step we configure
Emacs to ensure that it always inserts a terminating newline before
saving a file.

### Single Space for Sentence Spacing

Emacs uses the convention of treating a full stop followed by two
spaces as end of sentence.  However, many people these days seem to
prefer ending sentences with a full stop followed by a single space.
This section explains how to configure Emacs to treat a full stop
followed by a single space as end of sentence.

If you like the convention of having two spaces after full stop, you
should remove the code discussed below from your Emacs initialisation
file and then skip this section.  If you are unable to make up your
mind about whether you should end sentences with one space or two
spaces, read the final paragraph of this section for some discussion
about it.

We can configure Emacs to treat a sentence-terminating character (like
a full stop, question mark, etc.) followed by a single space as end of
sentence with the following code:

```elisp
(setq sentence-end-double-space nil)
```

This little setting has significant consequences while editing and
moving around text files.  We will discuss two such consequences now
with two tiny experiments:

**Experiment A: Moving By Sentences:** To check the default behaviour,
first comment out the above line of Emacs Lisp code in the Emacs
initialisation file, save the file, and restart Emacs.  Now copy the
following text:

```
Lorem ipsum dolor sit amet, consectetur adipiscing elit donec. Porttitor id lacus non consequat.
```

Then open a new text buffer in Emacs with `C-x C-f foo.txt RET` and
paste the copied text with `C-y`.  Then type `C-a` to go to the
beginning of the line.  Finally, type `M-e` to move to the end of the
sentence.  Without `sentence-end-double-space` set to `nil`, typing
`M-e` moves the cursor all the way to the end of the line (i.e., after
the second full stop).  It ignores the first full stop as end of
sentence because it is followed by one space whereas Emacs expects two
spaces at the end of a sentence.

Now to verify that the above line of Emacs Lisp code works as
expected, uncomment it again to enable it, save the file, restart
Emacs, and then perform the above experiment again.  With
`sentence-end-double-space` set to `nil`, typing `M-e` moves the
cursor to the end of the of first sentence (i.e., after the first full
stop).  This is what we normally expect these days.

**Experiment B: Filling Paragraphs:** While writing text files, it is
customary to limit the length of each line to a certain maximum
length.  In Emacs, the key sequence `M-q` invokes the `fill-paragraph`
command that works on the current paragraph and reformats it such that
each line is as long as possible without exceeding 70 characters in
length.

To check the default behaviour, first comment out the above line of
Emacs Lisp code in the Emacs initialisation file, save the file, and
restart Emacs.  Then create the same text buffer as the one in the
previous experiment.  Now place the cursor anywhere on text and type
`M-q` to reformat it as a paragraph.  Without
`sentence-end-double-space` set to `nil`, typing `M-q` reformats the
paragraph as follows:

```
Lorem ipsum dolor sit amet, consectetur adipiscing elit
donec. Porttitor id lacus non consequat.
```

Now to verify that the above line of Emacs Lisp code works as
expected, uncomment it again to enable it, save the file, then restart
Emacs, and then perform the above experiment again.  With
`sentence-end-double-space` set to `nil`, typing `M-q` reformats the
paragraphs as follows:

```
Lorem ipsum dolor sit amet, consectetur adipiscing elit donec.
Porttitor id lacus non consequat.
```

We see that without `sentence-end-double-space` set to `nil`, Emacs
refuses to insert a hard linebreak after the string `donec.`, so it
moves the entire word to the next line.  This is a result of following
the convention of double spaces at the end of a sentence.  This
convention prevents inadvertently placing a hard linebreak within an
abbreviation.  Since many people prefer ending a sentence with a
single space, we would like the text above to be reformatted as shown
in the last example above.  Setting `sentence-end-double-space` to
`nil` achieves this.

While the step above explains how to configure Emacs to treat a full
stop followed by a single space as the end of sentence, it is worth
mentioning here that the number of spaces that must follow the end of
a sentence is a very controversial matter.  Many people prefer two
spaces between sentences while many others prefer a single space
instead.  Section [Sentences][emacs-sentences-doc] of the Emacs manual
recommends putting two spaces at the end of a sentence because it
helps the Emacs commands that operate on sentences distinguish between
dots that end a sentence and those that do not.  The author of this
project uses two spaces to end sentences.  Also, see the [Opinion
References](#opinion-references) section for more discussion on this
topic.  In case, you want to follow the convention of two spaces at
the end of a sentence, omit the above line of Emacs Lisp from your
Emacs initialisation file.

[emacs-sentences-doc]: https://www.gnu.org/software/emacs/manual/html_node/emacs/Sentences.html

### Indentation

The following point shows how to configure Emacs to insert spaces, not
tabs, for indenting code.

- Use spaces, not tabs, for indentation:

```elisp
    (setq-default indent-tabs-mode nil)
    ```

Emacs uses a mix of tabs and spaces by default for indentation and
    alignment.  To verify the default behaviour, first comment out the
    above line of Emacs Lisp code, save it, then restart Emacs, then
    open a new Emacs Lisp source file, say, `C-x C-f foo.el RET` and
    type the following three lines of Emacs Lisp code:

```elisp
    (defun foo ()
      (concat "foo"
              "bar"))
    ```

While typing the above code, do not type <kbd>tab</kbd> or
    <kbd>space</kbd> to indent the second and third lines.  When you
    type <kbd>enter</kbd> at the end of each line, Emacs automatically
    inserts the necessary tabs and spaces to indent the code.  After
    entering this code, type `M-x whitespace-mode RET` to visualise
    whitespace characters.  This mode displays each space with a
    middle dot (`·`) and each tab with a right pointing guillemet
    (`»`).  With whitespace mode enabled, you should find that the
    second line of code is indented with two spaces but the third line
    is indented with a single tab followed by two spaces.  The buffer
    should look like this:

```elisp
    (defun·foo·()$
    ··(concat·"foo"$
    »       ··"bar"))
    ```

Emacs has a `tab-width` variable that is set to `8` by default.
    For every `tab-width` columns of indentation, Emacs inserts a tab
    to indent the code.  The third line requires 10 leading spaces for
    alignment, so Emacs inserts one tab character followed by two
    spaces to make the third line look aligned.  However, this code
    would look misaligned with a different `tab-width` setting.
    That's why we configure Emacs to use only spaces to indent and
    align code.

Now to verify that the above line of Emacs Lisp code works as
    expected, uncomment the function call to set `indent-tabs-mode` to
    `nil`, save it, then restart Emacs, and then perform the above
    experiment involving the three lines of Emacs Lisp code again.
    This time, you should see that no tabs are used for indentation.
    Only spaces are used for indentation.  Typing `M-x whitespace-mode
    RET` would display this in the buffer:

```elisp
    (defun·foo·()$
    ··(concat·"foo"$
    ··········"bar"))
    ```

In some type of files, we must use literal tabs.  For example, in
    `Makefile`, the syntax of target rules require that the commands
    under a target are indented by literal tab characters.  In such
    files, Emacs is smart enough to always use literal tabs for
    indentation regardless of the above variable setting.

Mixing tabs and spaces for indenting source code can be
    problematic, especially, when the author of code or Emacs
    inadvertently uses tabs for alignment (as opposed to using tabs
    for indentation only which would be fine) and another programmer
    views the file with an editor with a different tab width setting.
    In fact, in the experiment above, Emacs did use a literal tab
    character to align code which would cause the code to look
    misaligned on another editor with a different tab width setting.
    See [Tabs Are Evil](https://www.emacswiki.org/emacs/TabsAreEvil)
    for more details on this topic.

- Display the distance between two tab stops as whitespace that is
    as wide as 4 characters:

```elisp
    (setq-default tab-width 4)
    ```

Note that this primarily affects how a literal tab character is
    displayed.  Further, along with the previous variable setting
    where we set `indent-tabs-mode` to `nil`, in some types of files,
    this variable setting decides how many spaces are inserted when we
    hit the <kbd>tab</kbd> key.  For example, in text buffers, on
    hitting the <kbd>tab</kbd> key, as many spaces are inserted as are
    necessary to move the cursor to the next tab stop where the
    distance between two tab stops is assumed to be `tab-width`.

In some type of files, we must use literal tabs.  For example, in
    `Makefile`, the syntax of target rules require that the commands
    under a target are indented by a literal tab character.  In such
    files, Emacs displays the distance between two tab stops as
    whitespace that is as wide as 8 characters by default.  This
    default setting is often too large for many users.  They feel that
    a tab width of 8 consumes too much horizontal space on the screen.
    The variable setting above reduces the tab width to 4.  Of course,
    different users may have different preferences for the tab width.
    Therefore, users are encouraged to modify this variable setting to
    a value they prefer or omit the above line of Emacs Lisp code from
    their Emacs initialisation file to leave it to the default value
    of 8.

- Set indentation levels according to popular coding conventions for
    various languages:

```elisp
    (setq c-basic-offset 4)
    (setq js-indent-level 2)
    (setq css-indent-offset 2)
    ```

Emacs uses 2 spaces for indentation in C by default.  We change
    this to 4 spaces.

Emacs uses 4 spaces for indentation in JavaScript and CSS by
    default.  We change this to 2 spaces.

### Keep Working Directory Tidy

Emacs creates a number of temporary files to ensure that we do not
inadvertently lose our work while editing files.  However, these files
can clutter our working directories.  This section shows some ways to
keep the current working directory tidy by asking Emacs to manage
these files at a different location.

- Create a directory to keep auto-save files:

```elisp
    (make-directory "~/.tmp/emacs/auto-save/" t)
    ```

In the next point, we discuss auto-save files in detail and ask
    Emacs to write auto-save files to a separate directory instead of
    writing them to our working directory.  Before we do that, we need
    to create the directory we will write the auto-save files to,
    otherwise Emacs would fail to write the auto-save files and
    display the following error: `Error (auto-save): Auto-saving
    foo.txt: Opening output file: No such file or directory,
    /Users/susam/.tmp/emacs/auto-save/#!tmp!foo.txt#`

Note that this issue occurs only for auto-save files, not for
    backup files discussed in the third point of this list.  If the
    parent directory for backup files is missing, Emacs creates it
    automatically.  However, Emacs does not create the parent
    directory for auto-save files automatically, so we need the above
    line of Emacs Lisp code to create it ourselves.

- Write auto-save files to a separate directory:

```elisp
    (setq auto-save-file-name-transforms '((".*" "~/.tmp/emacs/auto-save/" t)))
    ```

If we open a new file or edit an existing file, say, `foo.txt` and
    make some changes that have not been saved yet, Emacs
    automatically creates an auto-save file named `#foo.txt#` in the
    same directory as `foo.txt` every 300 keystrokes, or after 30
    seconds of inactivity.  Emacs does this to ensure that the unsaved
    changes are not lost inadvertently.  For example, if the system
    crashes suddenly while we are editing a file `foo.txt`, the
    auto-save file would keep a copy of our unsaved worked.  The next
    time we try to edit `foo.txt`, Emacs would warn that auto-save
    data already exists and it would then suggest us to recover the
    auto-save data using `M-x recover-this-file RET`.  These auto-save
    files are removed automatically after we save our edits but until
    then they clutter our working directories.  The above line of
    Emacs Lisp code ensures that all auto-save files are written to a
    separate directory, thus leaving our working directories tidy.

- Write backup files to a separate directory:

```elisp
    (setq backup-directory-alist '(("." . "~/.tmp/emacs/backup/")))
    ```

If we create a new file or edit an existing file, say, `foo.txt`,
    then make some changes to it, and save it, the previous copy of
    the file is saved as a backup file `foo.txt~`.  These backup files
    too clutter our working direcories.  The above line of Emacs Lisp
    code ensures that all backup files are written to a separate
    directory, thus leaving our working directories tidy.

- Create backup files by copying our files, not moving our files:

```elisp
    (setq backup-by-copying t)
    ```

Everytime Emacs has to create a backup file, it moves our file to
    the backup location, then creates a new file at the same location
    as that of the one we are editing, copies our content to this new
    file, and then resumes editing our file.  This causes any hard
    link referring to the original file to be now referring to the
    backup file.

To experience this problem due to the default behaviour, first
    comment out the above line of Emacs Lisp code in the Emacs
    initialisation file, save the file, and restart Emacs.  Then
    create a new file along with a hard link to it with these
    commands: `echo foo > foo.txt; ln foo.txt bar.txt; ls -li foo.txt
    bar.txt`.  The output should show that `foo.txt` and `bar.txt`
    have the same inode number and size because they both refer to the
    same file.  Now run `emacs foo.txt` to edit the file, add a line
    or two to the file, and save the file with `C-x C-s`.  Now run `ls
    -li foo.txt bar.txt` again.  The output should show that `foo.txt`
    now has a new inode number and size while `bar.txt` still has the
    original inode number and size.  The file `bar.txt` now refers to
    the backup file instead of referring to the new `foo.txt` file.

To see the improved behaviour with the above line of Emacs Lisp
    code, uncomment it to enable it again in the Emacs initialisation
    file, save the file, restart Emacs and perform the same experiment
    again.  After we save the file, we should see that both `foo.txt`
    and `bar.txt` have the same inode number and size.

- Disable lockfiles:

```elisp
    (setq create-lockfiles nil)
    ```

As soon as we make an edit to a file, say `foo.txt`, Emacs creates
    a lockfile `.#foo.txt`.  If we then launch another instance of
    Emacs and try to edit this file, Emacs would refuse to edit the
    file, then warn us that the file is locked by another Emacs
    session, and provide us a few options regarding whether we want to
    steal the lock, proceed with editing anyway, or quit editing it.
    These lockfiles are removed automatically as soon as we save our
    edits but until then they clutter our directories.  Unlike
    auto-save files and backup files, there is no way to tell Emacs to
    write these files to a different directory.  We can however
    disable lockfile creation with the above line of Emacs Lisp code.

**Caution:** Note that disabling lockfiles could be risky if you
    are in the habit of launching multiple Emacs instances while
    editing files.  With such a habit, it is easy to make the mistake
    of opening the same file in two different Emacs instances and
    inadvertently overwrite changes made via one instance with changes
    made via another instance.  The lockfiles are hidden files anyway,
    so they should not bother you in directory listings.  If they
    bother you in, say, `git status` output, consider ignoring the
    lockfiles in `.gitignore` instead of disabling them.  Having said
    that, it may be okay to disable lockfiles if you are in the habit
    of launching only a single instance of Emacs for the entire
    lifetime of their desktop session and edit all files via that
    single instance.  The [Emacs Server](#emacs-server) and [Emacs
    Launcher](#emacs-launcher) sections later discuss techniques about
    how to make this usage style more convenient.  If you are willing
    to follow this style of using Emacs, then it may be okay to
    disable lockfiles.  To summarise, if you are in doubt, comment out
    or remove the above line of Emacs Lisp code to keep lockfiles
    enabled.

- When we install packages using `package-install` (coming up soon
    in a later section), a few customisations are written
    automatically into the Emacs initialisation file (e.g., in
    `~/.emacs.d/init.el`).  This has the rather undesirable effect of
    our carefully handcrafted `init.el` being meddled by
    `package-install`.  To be precise, it is the `custom` package
    invoked by `package-install` that intrudes into our Emacs
    initialisation file.  To prevent that, we ask `custom` to write
    the customisations to a separate file with the following code:

```elisp
    (setq custom-file (concat user-emacs-directory "custom.el"))
    ```

- Emacs does not load the custom-file automatically, so we add the
    following code to load it:

```elisp
    (load custom-file t)
    ```

It is important to load the custom-file because it may contain
    customisations we have written to it directly or via the customise
    interface (say, using `M-x customize RET`).  If we don't load this
    file, then any customisations written to this file will not become
    available in our Emacs environment.

The boolean argument `t` ensures that no error occurs when the
    custom-file is missing.  Without it, when Emacs starts for the
    first time with our initialisation file and there is no
    custom-file yet, the following error occurs: `File is missing:
    Cannot open load file, No such file or directory,
    ~/.emacs.d/custom.el`.  Setting the second argument to `t`
    prevents this error when Emacs is run with our initialisation file
    for the first time.

### Custom Command and Key Sequences

In this section we will see how to make our own custom command.

- Create a very simple custom command to display the current time in
    the echo area at the bottom of the Emacs frame:

```elisp
    (defun show-current-time ()
      "Show current time."
      (interactive)
      (message (current-time-string)))
    ```

This creates an interactive function named `show-current-time`.
    An interactive function is an Emacs command that can be invoked
    with `M-x`.  For example, the above command can be invoked by
    typing `M-x show-current-time RET`.  On running this command, the
    current time appears in the echo area.

- Create a custom key sequence to invoke the command defined in the
    previous point:

```elisp
    (global-set-key (kbd "C-c t") 'show-current-time)
    ```

Now the same command can be invoked by typing `C-c t`.

- Create another custom key sequence to delete trailing whitespace
    using the `delete-trailing-whitespace` introduced in the [Show
    Stray Whitespace](#show-stray-whitespace) section:

```elisp
    (global-set-key (kbd "C-c d") 'delete-trailing-whitespace)
    ```

Note that the custom key sequence in this point and the previous
    one only serve as examples.  You should define key sequences based
    on your needs that you find more convenient.

### Emacs Server

Many users prefer to run a single instance of Emacs and do all their
editing activities via this single instance.  It is possible to use
Emacs alone for all file browsing needs and never use the terminal
again.  Despite the sophisticated terminal and file browsing
capabilities of Emacs, some users still like to use a traditional
terminal to move around a file system, find files, and edit them.
This practice may become inconvenient quite soon because it would lead
to the creation of too many Emacs frames (desktop-level windows) and
processes.  This section explains how to create a single Emacs server,
a single Emacs frame, and edit all your files in this frame via the
server even while you are browsing files in the terminal.  You don't
need this section if you use Emacs for all your file browsing needs
but if you don't, this section may be useful.  Let us now see how we
start the Emacs server in our Emacs initialisation file.

- This is necessary to use the function `server-running-p` coming up
    in the next point:

```elisp
    (require 'server)
    ```

If we omit the above line of Emacs Lisp code, we will encounter
    the following error when we try to use `server-running-p`
    discussed in the next point: `Symbol’s function definition is
    void: server-running-p`.

- If there is no Emacs server running, start an Emacs server:

```elisp
    (unless (server-running-p)
      (server-start))
    ```

The `unless` expression ensures that there is no Emacs server
    running before starting a new Emacs server.  If we omit the
    `unless` expression, the following error would occur if an Emacs
    server is already running: `Warning (server): Unable to start the
    Emacs server. There is an existing Emacs server, named "server".
    To start the server in this Emacs process, stop the existing
    server or call ‘M-x server-force-delete’ to forcibly disconnect
    it.`

Finally, the `server-start` function call starts an Emacs server.

When Emacs starts for the first time with the above lines of Emacs
Lisp code in its initialisation file, it starts an Emacs server.  Now
the following commands can be used on a terminal to edit files:

- `emacs` or `emacs foo.txt bar.txt`: Starts another instance of
    Emacs.  It does not start a new server due to the `unless`
    expression discussed above.  Typically, we will not use this
    because we don't want to launch a second instance of Emacs.  But
    it is good to know that this command still works as expected in
    case we ever need it.

- `emacsclient foo.txt bar.txt`: Opens files in the existing Emacs
    instance via the Emacs server.  The command waits for us to finish
    editing all the files.  It blocks the terminal until then.  When
    we are done editing a file, we must type `C-x #` to tell Emacs to
    switch to the next file.  Once we are done editing all the files,
    the `emacsclient` command exits and the shell prompt returns on
    the terminal.

- `emacsclient -n foo.txt bar.txt`: Opens files in the existing
    Emacs instance but does not wait for us to finish editing.  The
    command exits immediately and the shell prompt returns immediately
    on the terminal.

With this setup, the Emacs server quits automatically when we close
the first Emacs instance that started the Emacs server.  Running the
`emacs` command or starting Emacs via another method after that would
start the Emacs server again.

It is worth noting here that there are other ways to start the Emacs
server and to use the `emacsclient` command.  See section [Using Emacs
as a Server][emacs-server-doc] and section [`emacsclient`
Options][emacs-client-doc] of the Emacs manual for more details.

[emacs-server-doc]: https://www.gnu.org/software/emacs/manual/html_node/emacs/Emacs-Server.html
[emacs-client-doc]: https://www.gnu.org/software/emacs/manual/html_node/emacs/emacsclient-Options.html

### Install Packages

The following points describe how we automate the installation of
Emacs packages we need:

- We begin defining a new command that we use to install external
    packages automatically.

```elisp
    (defun install-packages ()
      "Install and set up packages for the first time."
      (interactive)
      (require 'package)
    ```

The `(require 'package)` line is necessary for defining the
    `package-archives` list we will use in the next point.

- Add Milkypostman's Emacs Lisp Package Archive (MELPA) to the list
    of archives to fetch packages from:

```elisp
      (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
    ```

By default GNU Emacs Lisp Package Archive (ELPA) and NonGNU Emacs
    Lisp Package Archive (NonGNU ELPA) are the only package archives
    configured for fetching packages.  The above line adds MELPA too
    to the list of archives to fetch packages from.  Although we are
    not going to install any package from MELPA in this project, it is
    common practice to include it as a package source.  Adding MELPA
    now ensures you are prepared to explore a broader range of
    packages as your Emacs usage evolves.

- Download package descriptions from package archives:

```elisp
      (package-refresh-contents)
    ```

See the `~/.emacs.d/elpa/archives` or `~/.config/emacs/elpa/archives`
    directory for archive contents in case you are curious.

- Install some packages:

```elisp
      (dolist (package '(markdown-mode paredit rainbow-delimiters))
        (unless (package-installed-p package)
          (package-install package))))
    ```

This loop iterates over each package name in a list of packages.
    For each package, it checks whether the package is installed with
    the `package-installed-p` function.  If it is not installed, then
    it is installed with the `package-install` function.

You can modify the list of packages in the first line to add other
    packages that you might need in future or remove packages that you
    do not need.

The code discussed above creates a new command named
`install-packages` that we can execute anytime with
`M-x install-packages RET`.

You can also add new packages to the list used in the `dolist` call,
type `C-M-x` to evaluate the `install-packages` function again, so
that this command is now updated according to your latest code, and
then run `M-x install-packages RET` to install the new packages.

Having understood this section, step 4 of the [Get
Started](#get-started) section should now make sense.  The command we
used there was:

```sh
emacs --eval '(progn (install-packages) (kill-emacs))'
```

This command simply runs Emacs (with your Emacs initialisation file)
and evaluates an Emacs Lisp expression that runs the
`install-packages` function followed by `kill-emacs`.  As a result,
this command installs the packages configured in the code discussed
above and quits Emacs.

**Alternative:** If you know enough Emacs already, you might notice
that this project does not use the `use-package` package.  The
`use-package` package allows us to install and configure packages
declaratively such that the configuration of each package is neatly
contained within one `use-package` expression.  The author of this
project has been using Emacs long before `use-package` existed and
prefers a more traditional method of installing and configuring
packages using `package.el` and `with-eval-after-load`.  However, if
you want to explore installing and configuring packages declaratively,
please take a look at the [use-package User Manual][use-package].

[use-package]: https://www.gnu.org/software/emacs/manual/html_node/use-package/

### Configure Paredit

This section describes how to enable Paredit.  Paredit helps in
keeping parentheses balanced and in performing structured editing of
S-expressions.  Some Emacs Lisp programmers find it useful while some
do not.

In case you decide not to use Paredit, you may skip this section.  In
that case, you might also want to remove this package from the
`dolist` loop discussed in the previous section.

We enable Paredit in various modes pertaining to Lisp programming with
the following Emacs Lisp code:

```elisp
(when (fboundp 'paredit-mode)
  (dolist (hook '(emacs-lisp-mode-hook
                  eval-expression-minibuffer-setup-hook
                  ielm-mode-hook
                  lisp-interaction-mode-hook
                  lisp-mode-hook))
    (add-hook hook 'enable-paredit-mode)))
```

Here is an explanation of the above code:

- The `when` expression checks if `paredit-mode` is available before
    setting up hooks to enable it in various modes.  If it is
    unavailable, then the hooks are not set up.

- The `dolist` expression iterates over hooks for various modes
    where we want Paredit to be enabled.  In each iteration, the
    `add-hook` expression adds the function `enable-paredit-mode` to
    each mode's hook.  This ensures that whenever one of these modes
    gets activated, `enable-paredit-mode` is called thereby enabling
    Paredit in that mode.

- Adding `enable-paredit-mode` to `emacs-lisp-mode-hook` enables
    Paredit while editing Emacs Lisp code.

To test that Paredit is enabled while editing Emacs Lisp code,
    open a new Emacs Lisp file, say, `foo.el`.  Then type `(`.
    Paredit should automatically insert the corresponding `)`.

- Adding `enable-paredit-mode` to `eval-expression-minibuffer-setup-hook`
    enables Paredit in eval-expression minibuffer.

To test this, enter `M-:` to bring up the eval-expression minbuffer
    and type `(`.  Paredit should automatically insert the corresponding
    `)`.

- Adding `enable-paredit-mode` to `ielm-mode-hook` enables Paredit
    while interactively evaluating Emacs Lisp expressions in
    `inferior-emacs-lisp-mode` (IELM).

To test this, enter `M-x ielm RET`.  When the `*ielm*` buffer
    appears, type `(`.  Paredit should automatically insert the
    corresponding `)`.

- Adding `enable-paredit-mode` to `lisp-interaction-mode-hook`
    enables Paredit in Lisp interaction mode.

To test this, first open a non-Lisp file, say, `C-x C-f foo.txt
    RET`.  Now type `(`.  Note that no corresponding `)` is inserted
    because we are not in Lisp interaction mode yet.  Delete `(`.  Then
    start Lisp interaction mode with the command `M-x
    lisp-interaction-mode RET`.  Type `(` again.  Paredit should now
    automatically insert the corresponding `)`.

- Adding `enable-paredit-mode` to `lisp-mode-hook` enables Paredit
    while editing Lisp code other than Emacs Lisp.

To test this, open a new Common Lisp source file, say, `C-x C-f
    foo.lisp RET`.  Then type `(`.  Paredit should automatically insert
    the corresponding `)`.

By default, Paredit overrides the behaviour of the `RET` key such that
a newline is inserted whenever we press `RET` key.  Unfortunately,
this behaviour is problematic in the eval-expression minibuffer and
IELM where we want to evaluate the expression we have entered when we
type `RET`.  Therefore, we disable the overriding behaviour of Paredit
using the following code:

```elisp
(with-eval-after-load 'paredit
  (define-key paredit-mode-map (kbd "RET") nil))
```

The above code ensures that whenever Paredit is loaded, the `RET`
key binding in its keymap is set to `nil`, so that Paredit does
not override the default behaviour of the `RET` key.

### Configure Rainbow Delimiters

This section describes how to enable rainbow delimiters and configure
it.  Rainbow Delimiters colour nested parentheses with different
colours according to the depth level of each parenthesis.  Some people
find it useful and some do not.

If you decide not to use Rainbow Delimiters, you may skip this
section.  In that case, you might also want to remove this package
from the `dolist` loop discussed in the previous section.

We enable Paredit in various modes pertaining to Lisp programming with
the following Emacs Lisp code:

```elisp
(when (fboundp 'rainbow-delimiters-mode)
  (dolist (hook '(emacs-lisp-mode-hook
                  ielm-mode-hook
                  lisp-interaction-mode-hook
                  lisp-mode-hook))
    (add-hook hook 'rainbow-delimiters-mode)))
```

Here is an explanation of the above code:

- Then `when` expression checks if `rainbow-delimiters-mode` is
    available before setting up hooks to enable it in various modes.
    If it is unavailable, then the hooks are not set up.

- The `dolist` expression iterates over hooks for various modes
    where we want Rainbow Delimiters to be enabled.  In each
    iteration, the `add-hook` expression adds the function
    `rainbow-delimiters-mode` to each mode's hook.  This ensures that
    whenever one of these modes gets activated,
    `rainbow-delimiters-mode` is called thereby enabling Rainbow
    Delimiters in that mode.

- Adding `rainbow-delimiters-mode` to `emacs-lisp-mode-hook` enables
    Rainbow Delimiters while editing Emacs Lisp code.

To test this open a new Emacs Lisp file, say, `foo.el`.  Then type
    `(((`.  Rainbow Delimiters should colour each parenthesis
    differently.

- Adding `rainbow-delimiters-mode` to `ielm-mode-hook` enables
    Rainbow Delimiters while interactively evaluating Emacs Lisp
    expressions in inferior-emacs-lisp-mode (IELM):

To test this, enter `M-x ielm RET`.  When the `*ielm*` buffer comes
    up, type `(((`.  Rainbow Delimiters should colour each parenthesis
    differently.

- Adding `rainbow-delimiters-mode` to `lisp-interaction-mode-hook`
    enables Rainbow Delimiters in Lisp interaction mode.

To test this, first open a non-Lisp file, say, `foo.txt`.  Now type
    `(((`.  Then start Lisp interaction mode with the command `M-x
    lisp-interaction-mode RET`.  Rainbow Delimiters should now colour each
    parenthesis differently.

- Adding `rainbow-delimiters-mode` to `lisp-mode-hook` enables
    Rainbow Delimiters while editing Lisp code other than Emacs Lisp:

To test this, open a new Common Lisp source file, say, `foo.lisp`.
    Then type `(((`.  Rainbow Delimiters should colour each parenthesis
    differently.

In the discussion above, you may have noticed that we did not enable
Rainbow Delimiters for eval-expression minibuffer.  That is because
eval-expression minibuffer does not support syntax highlightng.
Therefore enabling Rainbow Delimiters in it has no effect.  See
https://github.com/Fanael/rainbow-delimiters/issues/57 for more
details.

The default colours that Rainbow Delimiters chooses for the nested
parentheses are too subtle to easily recognise the matching pair of
parentheses.  The following Emacs Lisp code makes the parentheses more
colourful:

```elisp
(with-eval-after-load 'rainbow-delimiters
  (set-face-foreground 'rainbow-delimiters-depth-1-face "#c66")  ; red
  (set-face-foreground 'rainbow-delimiters-depth-2-face "#6c6")  ; green
  (set-face-foreground 'rainbow-delimiters-depth-3-face "#69f")  ; blue
  (set-face-foreground 'rainbow-delimiters-depth-4-face "#cc6")  ; yellow
  (set-face-foreground 'rainbow-delimiters-depth-5-face "#6cc")  ; cyan
  (set-face-foreground 'rainbow-delimiters-depth-6-face "#c6c")  ; magenta
  (set-face-foreground 'rainbow-delimiters-depth-7-face "#ccc")  ; light gray
  (set-face-foreground 'rainbow-delimiters-depth-8-face "#999")  ; medium gray
  (set-face-foreground 'rainbow-delimiters-depth-9-face "#666")) ; dark gray
```

The colours chosen above make matching pairs of parentheses easier to
recognise.

### End of File

The final line of code in the file is:

```elisp
(provide 'init)
```

The above line is not really necessary for the Emacs initialisation
file.  The `provide` function call declares a feature that an Emacs
package provides, so `provide` calls like the one above are typically
found in Emacs packages.  Here, we simply declare that this Emacs
initialisation file provides a feature named `init`, only for the sake
of completeness.

Other Emacs Lisp programs can test whether a feature is availabe using
the `featurep` function.  For example, Paredit provides the feature
named `paredit`.  To test if this feature is available, type `M-:
(featurep 'paredit) RET`.

Similarly, to test if the `init` feature declared above is available,
type `M-: (featurep 'init) RET`

### Emacs Launcher

In the [Emacs Server](#emacs-server) section, we saw how our Emacs
initialisation file ensures that an Emacs server is started when we
run `emacs` for the first time.  Once Emacs server has started, we can
edit new files from the terminal using the `emacsclient` command.
This section describes a script named `em` that can automatically
decide whether to run `emacs` or `emacsclient` depending on the
situation.

As mentioned in the previous section, you don't need this section if
you use Emacs for all your file browsing needs but if you don't, this
section may be useful.  Further, it is worth mentioning that this
script solves a very specific problem of using a single command named
`em` to both launch a new Emacs server as well as to open existing
files in an existing Emacs frame via the existing Emacs server.  If you
have this specific problem, you may find this script helpful.  However,
if you do not have this problem or if you have a different problem to
solve, it would be useful to understand how `emacsclient` works and
read the related documentation mentioned in the previous section and
then modify this script or write your own shell script, shell alias,
or shell function that solves your problems.

The `em` script should be already present on the system if the steps
in the [Get Started](#get-started) section were followed.  The third
step there installs this script to `/usr/local/bin/em`.  Now we discuss
every line of this script in detail.

- When `em` is run without any arguments, start a new Emacs process:

```sh
    #!/bin/sh
    if [ "$#" -eq 0 ]
    then
        echo "Starting new Emacs process ..." >&2
        nohup emacs &
    ```

This Emacs process launches a new Emacs frame.  Further, if an
    Emacs server is not running, it starts a new Emacs server.  The
    `nohup` command ensures that this Emacs process is not terminated
    when we close the terminal or the shell where we ran the `em`
    command.

- When `em` is run with one or more filenames as arguments and there
    is an Emacs server already running, edit the files using the
    existing Emacs server:

```sh
    elif emacsclient -n "$@" 2> /dev/null
    then
        echo "Opened $@ in Emacs server" >&2
    ```

However, if there is no Emacs server already running, the above
    command in the `elif` clause fails and the execution moves to the
    `else` clause explained in the next point.

- When `em` is run with one or more filenames as arguments and there
    is no Emacs server running, start a new Emacs process to edit the
    files:

```sh
    else
        echo "Opening $@ in a new Emacs process ..." >&2
        nohup emacs "$@" &
    fi
    ```

The new Emacs process also starts a new Emacs server.

Now that we know what the `em` script does, let us see the various
ways of using this script as a command:

- `em`: Start a new instance of Emacs.  If there is no Emacs server
    running, this ends up starting an Emacs server too.  Normally, this
    command should be run only once after logging into the desktop
    environment.

- `em foo.txt bar.txt`: Edit files in an existing instance of Emacs
    via Emacs server.  If no Emacs server is running, this ends up
    starting an Emacs server automatically.  This command is meant to
    be used multiple times as needed for editing files while browsing
    the file system in a terminal.

That's it!  Only two things to remember from this section: start Emacs
with `em` and edit files with `em foo.txt`, `em foo.txt bar.txt`, etc.

Opinion References
------------------

- [Give paredit mode a chance][paredit-chance]
- [Never warmed up to paredit][paredit-never-warmed]
- [Coloring each paren differently only adds noise][rainbow-noise]
- [The drawbacks of using single space between sentences][single-space-drawbacks]
- [Why you should never, ever use two spaces after a period][space-invaders]

[paredit-chance]: https://stackoverflow.com/a/5243421/303363
[paredit-never-warmed]: https://lobste.rs/s/vgjknq/emacs_begin_learning_common_lisp#c_0y6zpd
[rainbow-noise]: https://lobste.rs/s/vgjknq/emacs_begin_learning_common_lisp#c_1n78vl
[single-space-drawbacks]: https://old.reddit.com/r/emacs/comments/p5zlr6/
[space-invaders]: https://slate.com/technology/2011/01/two-spaces-after-a-period-why-you-should-never-ever-do-it.html

Channels
--------

The following channels are available for asking questions, seeking
help and receiving updates regarding this project:

- GitHub: [emfy/issues](http://github.com/susam/emfy/issues)
- Mastodon: [@susam@mastodon.social](https://mastodon.social/@susam)
- Matrix: [#susam:matrix.org](https://matrix.to/#/#susam:matrix.org)
- Libera: [#susam](https://web.libera.chat/#susam)

You are welcome to follow or subscribe to one or more of these channels
to receive updates and ask questions about this project.

License
-------

This is free and open source software.  You can use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of it,
under the terms of the MIT License.  See [LICENSE.md][L] for details.

This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
express or implied.  See [LICENSE.md][L] for details.

[L]: LICENSE.md

emfy

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