19.4 Interactive Highlighting by Matching

It is sometimes useful to temporarily highlight text that matches a certain regular expression. For example, you might wish to see all the references to a certain variable in a program source file, highlight certain parts in a voluminous output of some program, or make certain names stand out in an article.

Use the M-x hi-lock-mode command to turn on a minor mode that allows you to interactively add and remove regular expressions specifying text to be highlighted. Hi Lock mode works like Font Lock mode (see Font Lock), except that it lets you easily add and remove regular expressions while you are editing a buffer. To enable Hi Lock mode for all buffers use M-x global-hi-lock-mode or place (global-hi-lock-mode 1) in your .emacs file.

You control Hi Lock mode with these commands:

C-x w h regexp <RET> face <RET>

Highlight text that matches regexp using face face (highlight-regexp). By using this command more than once, you can highlight various parts of the text in different ways. The highlighting will remain as long as the buffer is loaded. For example, to highlight all occurrences of the word “whim” using the default face (a yellow background) C-x w h whim <RET> <RET>. Any face can be used for highlighting, Hi Lock provides several of its own and these are pre-loaded into a history list. While being prompted for a face use M-p and M-n to cycle through them.

C-x w r regexp <RET>

Unhighlight regexp (unhighlight-regexp). When activated from the menu select the expression to unhighlight from a list. When activated from the keyboard the most recently added expression will be shown. Use M-p to show the next older expression and M-n to select the next newer expression. When the expression to unhighlight appears press <RET> to unhighlight it. The expression can also be typed and completion is available.

C-x w l regexp <RET> face <RET>

Highlight entire lines containing a match for regexp, using face face (highlight-lines-matching-regexp).

C-x w b

Insert all the current highlighting regexp/face pairs into the buffer at point, with comment delimiters to prevent them from changing your program. This key binding runs the hi-lock-write-interactive-patterns command.

These patterns will be read the next time you visit the file while Hi Lock mode is enabled, or whenever you use the M-x hi-lock-find-patterns command.

C-x w i

Re-read regexp/face pairs in the current buffer (hi-lock-write-interactive-patterns). Users familiar with Font Lock keywords might interactively enter patterns (highlight-regexp), write them into the file (hi-lock-write-interactive-patterns), edit them, perhaps including different faces for different parenthesized parts of the match, and finally use this command (hi-lock-write-interactive-patterns) to have Hi Lock highlight them.

This command does nothing if the major mode is a member of the list hi-lock-exclude-modes.