Emacs command to look for a regexp among versioned files in a Git repo

git-grep-dired.el

(defun git-grep-dired (repo wildcards regexp)
  "Find Git-controlled files in DIR with a name like WILDCARDS containing a regexp REGEXP and start Dired on output."
  (interactive "DGit-grep (directory): \nsGit-grep (filename wildcard(s), e.g. *.xml): \nsGit-grep (grep regexp): ")
  (setq repo (file-name-as-directory (expand-file-name repo)))
  (switch-to-buffer (concat "*Git Grep " repo "*"))
  (fundamental-mode)
  (setq buffer-read-only nil)
  (erase-buffer)
  (setq default-directory repo)
  (let ((cmd (format "git --git-dir %s/.git ls-files --recurse-submodules -z%s | xargs -0 grep -lZ -- %s | xargs -0 ls -l"
                     repo
                     (apply 'concat (mapcar (lambda (s) (concat " " (shell-quote-argument s))) (split-string wildcards)))
                     (shell-quote-argument regexp))))
    (insert "  " cmd "\n  " repo ":\n")
    (call-process-shell-command (concat cmd " | sed -e 's/^/  /g'") nil t))
  (dired-mode)
  (dired-build-subdir-alist)
  (goto-line 2))