a.el

(setenv "PERL5LIB" (concat "./lib:" (getenv "PERL5LIB")))
(setenv "PATH" (concat (getenv "HOME") "/.plenv/shims:" (getenv "HOME") "/.plenv/bin:" (getenv "PATH")))
(setq exec-path (cons (concat (getenv "HOME") "/.plenv/shims") (cons (concat (getenv "HOME") "/.plenv/bin") exec-path)))
(require 'plenv)    ; <M-x> package-install plenv
(plenv-global "5.18.1")

(defun flymake-perl-init ()
  (let* ((temp-file (flymake-init-create-temp-buffer-copy
                     'flymake-create-temp-with-folder-structure))
         (local-file (file-relative-name
                      temp-file
                      (file-name-directory buffer-file-name))))
    (list (guess-plenv-perl-path) (list "-wc" local-file))))

; https://github.com/tokuhirom/plenv
; https://github.com/karupanerura/plenv.el
; http://marc-bowes.com/2012/03/10/rbenv-with-emacs.html