Question

I’m a newbie to programming, so please bear with me here…

I have a directory full of files called “foo01.txt”, “foo02.txt”, etc. and a function called MyFunction. I want to open each file as a buffer, run MyFunction on it, write the buffer to its file, kill the buffer and move on to the next file in the series until all the files are done.

I think all the pieces I need to do this are described in the Cookbook (http://emacswiki.org/emacs/ElispCookbook) but I’m not really understanding how to put it all together. Thanks!

Answer 1

Answer

If you’re looking for an answer in pure elisp, you could do something like this:

(defun process-file (f)
  (save-excursion 
    (find-file f)
    (my-function)     ; Call your function here.
    (write-file f)
    (kill-buffer (current-buffer))))

(defun process-files (dir) 
  (mapc 'process-file
        (directory-files dir t ".txt$")))

process-files will iterate over each file in a given directory and apply process-file to all .txt files. You can call it like so:

(process-files "~/target-directory")

You can copy this into a *scratch* buffer and play around with the individual parts. The most interesting functions are:

• mapc – applies a function to each item in a list
• directory-files – gets all files and folders in a directory, in this case retrieving all .txt files
• find-file – opens a file in a buffer (this is what is run when you type C-x C-f)

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Learning Lisp

If you’re learning Lisp for its own sake, I can recommend Practical Common Lisp. You’ll be able to work through a surprising amount of the book using Elisp. Otherwise, download a Common Lisp environment like SBCL.