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Comb is a native Emacs Lisp solution to search, browse and annotate occurrences of regular expressions in files. The interactive interface allows to perform an exhaustive classification of all the results to rule out false positives and asses proper matches during code audit.



MELPA package

M-x package-install RET comb

Local package

M-x package-install-file RET /path/to/comb/


(add-to-list 'load-path "/path/to/comb/")
(require 'comb)


This is a quick walkthrough of some of the features of Comb. To perform a search:

  1. move to the root directory of the repository you want to audit;

  2. run M-x comb;

  3. press c to enter the configuration mode;

  4. fill the desired fields and finally perform a search.


If there are some results to browse then the *Comb* buffer is displayed, from here it is possible to annotate the results (!) and change their status to approved (a/A), rejected (r/R) or undecided (u/U, the default).

The above actions work on the current result which can be moved to the next (n) or the previous (p), in doing so the *Comb* buffer is updated to show the file that contains the result, which is now highlighted. Only results matching the status filter (cycled with f) and the notes filter regexp (set with F) are displayed. In addition to that, t spawns a buffer containing the list of the currently displayed results, this allows to Isearch the snippets and jump to the result at point.


Finally it is possible to save the current session to file (s) and load it back to resume the audit (l).

See the help (h) for a list of all the features and keybindings.


The patterns used by Comb are Emacs-flavored regexps (see the (elisp) Regular Expressions info node). The M-x regexp-builder utility can be used to interactively try the regexps before performing a search, just make sure to use the proper syntax (C-c TAB string) and leave out the surrounding ".


Comb also accepts a list of callbacks that can be used to generate additional search results, e.g., coming from an external linting tool. These functions are executed with the default-directory set to the root directory and the current buffer set to the currently processed file, they accept a relative path as an argument and must return a list of ranges in the form (BEGIN . END).

Here is an example callback:

(defun my-callback (filename)
  "Match only the first occurrence of 'qwerty'."
  (when (re-search-forward "qwerty" nil t)
    (list (cons (match-beginning 0) (match-end 0)))))

Errors in the callback execution are not fatal, they are just reported in the *Messages* buffer.


Some faces and options can be configured, take a look at the comb customization group (M-x customize-group RET comb).

Additionally, all the keybindings in the *Comb* buffer can be altered by changing the comb-keymap keymap. For example, to use the arrows to navigate the results use:

(define-key comb-keymap (kbd "<left>") 'comb-prev)
(define-key comb-keymap (kbd "<right>") 'comb-next)

This does not unbind the original keybindings though. It may be convenient to completely replace the keymap instead so to avoid collisions with existing modes:

(setq comb-keymap (make-sparse-keymap))
(define-key comb-keymap (kbd "x") 'comb-quit)
(define-key comb-keymap (kbd "?") 'comb-help)
(define-key comb-keymap (kbd "<left>") 'comb-prev)
(define-key comb-keymap (kbd "<right>") 'comb-next)
;; ...

See the comb-default-keybindings alist to obtain the functions used by the default keybindings.


Interactive code auditing and grep tool in Emacs Lisp





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