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HOWTO: Invoke a shell script on a file on save with emacs

At my current job, we use a lot of Template Toolkit. Due to some design decisions (that I consider a tad strange), we have to run a shell script on the template files (e.g. files that end with “.tt”) after they are saved in order for them to be displayed on the dev site.

Since I started using emacs about two months ago, I’ve learned quite a bit. A new thing on the learning heap is the after-save-hook. Emacs to the rescue yet again.

Here’s a emacs lisp function I wrote to automate the execution of the script when a template file is saved:

(defun ssm-cheetah-after-save-hook ()
  "After saving a tt file, run the language_update file"
  (if buffer-file-name
      (progn
        (setq is-tt-file (numberp (string-match "\.tt$" buffer-file-name)))
        (if is-tt-file
            (progn
              (setq cmd (concat (getenv "B") "/bin/YOURSCRIPTHERE --template="))
              (shell-command (concat cmd buffer-file-name))
              (message "Updated template with %s" buffer-file-name))))))
(add-hook 'after-save-hook 'ssm-cheetah-after-save-hook)

What it does, is first defines a function that checks to see if we have a file name, (which should probably always be true since we are saving now that I look at it). If we do, check to see if the name ends with “.tt.” If it does, pass the name of the file to the shell script and output a message to the user saying the template was updated. Finally, the function is added to the after save hook.