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I am writing an org file that org babel will tangle into "custom.el" as shown here and here.

My problem is that on one machine the path to my agenda files is C:/Users/Username/Dropbox/file.org while on anther machine it is C:/Users/DifferentUserName/Dropbox/file.org.

I can setq the org-directory to the the correct path on different machines with: 

(setq org-directory 
  (car  ;; with car returned value is type 'string' witout car returned type is 'cons'  
      (delq nil
         (mapcar (lambda(x) (and (file-directory-p x) x))
                       '("c:/Users/marka/Dropbox/Apps/OrgMode"
                         "c:/Users/Mark/Dropbox/Apps/OrgMode"
                         "c:/Users/msmith/Dropbox/Apps/OrgMode")))))

With a single agenda file, using concat (concat org-directory "/gtd_work.org") returns the desired path to the agenda file "c:/Users/Mark/Dropbox/Apps/OrgMode/gtd_work.org".

Unfortunately multiple uses of the concat function when nested in the setq appears to stop functioning:

>  (setq org-agenda-files                             
>             '((concat org-directory "/gtd_work.org")
>               (concat org-directory "/gtd_proging.org")
>               (concat org-directory "/gtd_home.org")
>               (concat org-directory "/DailyRoutine.org")))

Using C-h v to find the value of org-agenda-files yields: 

org-agenda-files is a variable defined in `org.el'.
Its value is ((concat org-directory "/gtd_work.org")
 (concat org-directory "/gtd_proging.org")
 (concat org-directory "/gtd_home.org")
 (concat org-directory "/DailyRoutine.org"))

Additionally I have tried:

  1. Removing the single quote in the setq, this raises an Invalid function: (concat org-directory "/gtd_work.org") exception.
  2. mapcar and mapc raise Wrong type argument: stringp, (concat org-directory "/gtd_work.org") exceptions.
  3. Using ~/file.org without concat returns nil

I am doing this in scratch right now as config.org is w.i.p. Will org concat the path to the agenda files? Am I not using concat correctly? If I write out the full path for each file on each computer and use (mapcar (lambda (x) (and (file-exists-p x) x)) it will correctly select the machine specific path, however, this results in the first world problem of having to specify 20~40 paths rather than 8~12.

Solution by amitp below works for both the setq and for the:

(setq org-agenda-files
      (delq nil
            (mapcar (lambda (x) (and (file-exists-p x) x))

Thanks everyone for the help.

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  • 1
    How about programmatically distinguishing between machines and just live with different paths? For example, evaluate (x-server-version) and/or use other methods to distinguish the OS, etc. -- e.g., system-type; feature-p 'ns, etc. That way, the paths will be programmatically adjusted depending upon which computer you are using. To synchronize, I use rsync instead of Dropbox and I do it manually as needed. I sync my whole installation to desktops and laptops, and to an iPhone (backup) and up to a shared web server (backup).
    – lawlist
    Jun 18, 2016 at 4:08
  • 1
    Please place a check-mark next to the correct answer; and, if you are happy with either of the answers, then click the up-arrow button to give them a an extra brownie-point. In addition to @amitp answer below, you can also use a back-tick instead of a single-quote and place a comma before anything in the list that needs to be evaluated. I can't do a back-tick in a comment because of the formatting that stackexchange uses, so I can't do a demonstration of the back-tick -- here is a comma demonstration though: ,(concat ....) Perhaps @amitp could update the answer with another example.
    – lawlist
    Jun 19, 2016 at 20:56
  • Tick done, I did try and up vote earlier but as I have only been "writing" elisp for 2 days now I have not been around enough to collect the required 15 reputation. I appreciate the guidance on protocol as well.
    – MarkSmithlxviii
    Jun 19, 2016 at 21:18
  • Backticks are a little tricky but yes, … `(,(concat …) ,(concat …)) will be the same as (list (concat …) (concat …)) in this case. Backtick/comma is useful when you want to partially quote something, but some piece of it you want to evaluate without the quotes.
    – amitp
    Jun 19, 2016 at 23:54

2 Answers 2

Reset to default
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The single quote (') tells lisp not to evaluate(run) the thing, but to leave it as is. When you write '((concat org-directory "/gtd_work.org") …) it tells it not to actually run the concat function, but instead leave the word "concat" in there. When you removed the ' it didn't work either because it didn't know that you wanted all those things put into a list. The good news is that it's easy to make them into a list: the function name is list so you replace '(…) with (list …).

Try changing

(setq org-agenda-files
         '((concat org-directory "/gtd_work.org")
           (concat org-directory "/gtd_proging.org")
           (concat org-directory "/gtd_home.org")
           (concat org-directory "/DailyRoutine.org")))

to

(setq org-agenda-files
         (list
           (concat org-directory "/gtd_work.org")
           (concat org-directory "/gtd_proging.org")
           (concat org-directory "/gtd_home.org")
           (concat org-directory "/DailyRoutine.org")))
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3

Instead of using just the string value, perhaps use expand-file-name? I believe this expands to the correct cross platform value on windows.

You could define a user constant to make it easy to use in multiple places, just like this bit from spacemacs core:

(defconst user-home-directory
  (expand-file-name "~/")
  "User home directory (~/).")
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