Replace helm grep with ag (The Silver Searcher)

helm-ag.el

  ;; Replace the default helm grep command with ag.
  ;; Requires "The Silver Searcher" (ag) to be installed.
  ;; On macOS use: 'brew install the_silver_searcher'
  (when (executable-find "ag")
    ;; For helm to recognize correctly the matches we need to enable
    ;; line numbers and columns in its output, something the
    ;; --vimgrep option does.
   (setq helm-grep-default-command         "ag --vimgrep --nogroup --nocolor -z %p %f"
         helm-grep-default-recurse-command "ag --vimgrep --nogroup --nocolor -z %p %f"))