27.6.2 Init File Examples

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

• 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. 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.

• 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 the mode we want. A single-quote is written before it to make a symbol constant; otherwise, text-mode would be treated as a variable name.

• Turn on Auto Fill mode automatically in Text mode and related modes.

  (setq text-mode-hook
    '(lambda () (auto-fill-mode 1)))
  

  Here we have a variable whose value should be a Lisp function. The function we supply is a list starting with lambda, and a single quote is written in front of it to make it (for the purpose of this setq) a list constant rather than an expression. Lisp functions are not explained here; for mode hooks it is enough to know that (auto-fill-mode 1) is an expression that will be executed when Text mode is entered. You could replace it with any other expression that you like, or with several expressions in a row.

  (setq text-mode-hook 'turn-on-auto-fill)
  

  This is another way to accomplish the same result. turn-on-auto-fill is a symbol whose function definition is (lambda () (auto-fill-mode 1)).

• 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 pathname, not starting with ‘/’ or ‘~’, load searches the directories in load-path (see Loading).

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

  (load "~/foo.elc")
  

  Here an absolute file name is used, so no searching is done.

• Rebind the key C-x l to run the function make-symbolic-link.

  (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 C mode only.

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

• Bind the function key F1 to a command in C mode. Note that the names of function keys must be lower case.

  (define-key c-mode-map 'f1 'make-symbolic-link)
  

• Bind the shifted version of F1 to a command.

  (define-key c-mode-map '(shift f1) 'make-symbolic-link)
  

• Redefine all keys which now run next-line in Fundamental mode to 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 would make C-x C-v a prefix, but C-x C-v must be freed of any non-prefix definition first.

• 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 eval-expression without confirmation.

  (put 'eval-expression 'disabled nil)