Conditional switch to file on startup

Question

I'm using spacemacs and currently I'm using the following in my user-config to switch to the scratch buffer when emacs starts:

(setq inhibit-splash-screen t)
(switch-to-buffer "*scratch*")

However, I want to adapt that code to open an org file instead. The issue is that I run the same config on 3 different computers and the location of the file is different for each:

• ~/Dropbox/myfile.org
• C:\Dropbox\myfile.org
• D:\Dropbox\myfile.org

How do I add some condition checking so that:

1. If I'm on OSX or Linux, load the org file from ~/Dropbox/myfile.org
2. If I'm on Windows and the file exists, load it from D:\Dropbox\myfile.org
3. If I'm on Windows and #2 doesn't exist, load it from C:\Dropbox\myfile.org

My issue is differentiating between case 2 and 3. Case 1 can be handled by checking system-type, but on my desktop I have multiple hard drives so I keep Dropbox on D:\, but on my laptop I only have 1 SSD so Dropbox is on C:\, and need a way to figure out the correct path to the file on both Windows systems

Answer 1

You can check if a file exists with file-exists-p. From its documentation:

Return t if file FILENAME exists (whether or not you can read it.)

Note that this won't throw an error if you're, say, on Windows and trying to read ~/myfile.org. So we can just loop over all the possible files and take the first one that exists:

(loop for filename in '("~/Dropbox/myfile.org" "C:\\Dropbox\\myfile.org" "D:\\Dropbox\\myfile.org")
      when (file-exists-p filename) collect filename into valid-files
      finally return (car valid-files))

This will return the first file that exists, which you can assign to a variable or open directly.