Highlighting automatically on file open

Question

I would like to highlight lines with a certain pattern whenever the file is opened.

Specifically when Journal.org is opened I want to run commands like M-s h l to highlight a set of patterns and assign them background colors.

What is the simplest way to go about doing this (without writing a lot of custom elisp code)?

Answer 1

The hi-lock package has support for saving patterns to a file and re-applying them.

1. Use the standard hi-lock commands to highlight what you are interested in. For example, use M-s h l to highlight lines matching some pattern.
2. Use M-s h w (hi-lock-write-interactive-patterns) to save the current highlight patterns to the file as a special comment line.
3. Enable hi-lock-mode or global-hi-lock-mode. For example, if you're only using highlighting in org files you could enable hi-lock mode in an org-mode hook.

The next time you visit that file and hi-lock is enabled, you will be prompted whether you want to highlight the found patterns. You can customize hi-lock-file-patterns-policy if you don't want to be prompted.

Answer 2

This is a classic case where elisp can help you:

(defun my-highlight ()
  (if (string-equal "Journal.org"
                    (file-name-nondirectory buffer-file-name))
      (highlight-lines-matching-regexp "foo" 'hi-yellow)))

(add-hook 'find-file-hook #'my-highlight)