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#### 51.4.2 Init File Examples

Here are some examples of doing certain commonly desired things with Lisp expressions:

- Add a directory to the variable `load-path`. You can then put Lisp libraries that are not included with Emacs in this directory, and load them with `M-x load-library`. See Lisp Libraries.

      (add-to-list 'load-path "/path/to/lisp/libraries")

- Make `TAB` in C mode just insert a tab if point is in the middle of a line.

      (setq c-tab-always-indent nil)

  Here we have a variable whose value is normally `t` for “true” and the alternative is `nil` for “false”.

- Make searches case sensitive by default (in all buffers that do not override this).

      (setq-default case-fold-search nil)

  This sets the default value, which is effective in all buffers that do not have local values for the variable (see Locals). Setting `case-fold-search` with `setq` affects only the current buffer’s local value, which is probably not what you want to do in an init file.

- Specify your own email address, if Emacs can’t figure it out correctly.

      (setq user-mail-address "cheney@torture.gov")

  Various Emacs packages, such as Message mode, consult `user-mail-address` when they need to know your email address. See Mail Headers.

- Make Text mode the default mode for new buffers.

      (setq-default major-mode 'text-mode)

  Note that `text-mode` is used because it is the command for entering Text mode. The single-quote before it makes the symbol a constant; otherwise, `text-mode` would be treated as a variable name.

- Set up defaults for the Latin-1 character set which supports most of the languages of Western Europe.

      (set-language-environment "Latin-1")

- Turn off Line Number mode, a global minor mode.

      (line-number-mode 0)

- Turn on Auto Fill mode automatically in Text mode and related modes (see Hooks).

      (add-hook 'text-mode-hook 'auto-fill-mode)

- Load the installed Lisp library named `foo` (actually a file `foo.elc` or `foo.el` in a standard Emacs directory).

      (load "foo")

  When the argument to `load` is a relative file name, not starting with ‘`/`’ or ‘`~`’, `load` searches the directories in `load-path` (see Lisp Libraries).

- Load the compiled Lisp file `foo.elc` from your home directory.

      (load "~/foo.elc")

  Here a full file name is used, so no searching is done.

- Tell Emacs to find the definition for the function `myfunction` by loading a Lisp library named `mypackage` (i.e., a file `mypackage.elc` or `mypackage.el`):

      (autoload 'myfunction "mypackage" "Do what I say." t)

  Here the string `"Do what I say."` is the function’s documentation string. You specify it in the `autoload` definition so it will be available for help commands even when the package is not loaded. The last argument, `t`, indicates that this function is interactive; that is, it can be invoked interactively by typing `M-x myfunction RET` or by binding it to a key. If the function is not interactive, omit the `t` or use `nil`.

- Rebind the key `C-x l` to run the function `make-symbolic-link` (see Init Rebinding).

      (global-set-key "\C-xl" 'make-symbolic-link)

  or

      (define-key global-map "\C-xl" 'make-symbolic-link)

  Note once again the single-quote used to refer to the symbol `make-symbolic-link` instead of its value as a variable.

- Do the same thing for Lisp mode only.

      (define-key lisp-mode-map "\C-xl" 'make-symbolic-link)

- Redefine all keys which now run `next-line` in Fundamental mode so that they run `forward-line` instead.

      (substitute-key-definition 'next-line 'forward-line
                                 global-map)

- Make `C-x C-v` undefined.

      (global-unset-key "\C-x\C-v")

  One reason to undefine a key is so that you can make it a prefix. Simply defining `C-x C-v anything` will make `C-x C-v` a prefix, but `C-x C-v` must first be freed of its usual non-prefix definition.

- Make ‘`$`’ have the syntax of punctuation in Text mode. Note the use of a character constant for ‘`$`’.

      (modify-syntax-entry ?\$ "." text-mode-syntax-table)

- Enable the use of the command `narrow-to-region` without confirmation.

      (put 'narrow-to-region 'disabled nil)

- Adjusting the configuration to various platforms and Emacs versions.

  Users typically want Emacs to behave the same on all systems, so the same init file is right for all platforms. However, sometimes it happens that a function you use for customizing Emacs is not available on some platforms or in older Emacs versions. To deal with that situation, put the customization inside a conditional that tests whether the function or facility is available, like this:

      (if (fboundp 'blink-cursor-mode)
          (blink-cursor-mode 0))

      (if (boundp 'coding-category-utf-8)
          (set-coding-priority '(coding-category-utf-8)))

  You can also simply disregard the errors that occur if the function is not defined.

      (ignore-errors (set-face-background 'region "grey75"))

  A `setq` on a variable which does not exist is generally harmless, so those do not need a conditional.

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