Why is ^M being added to a script.r after modifying with Meld?

Question

Esteemed Meld and Emacs/ESS users,

What I did:

1. Create a script.r using Emacs/ESS.
2. Make some modifications to script.r by pulling some lines of code from another_script.r
3. Reopen another_script.r (or script.r) in Emacs/ESS to continue working.

All the lines in another_script.r which were not pushed to script.r end with ^M

Some times it's the other way around - only the line that was pushed/pulled ends with ^M's. So far i haven't isolated exactly which action determines where the ^M's are placed. Either way i still end up with ^M's all over the place and i'd like to avoid getting them after using Meld!

FWIW: the directory is being synced by Dropbox; in Meld, Preferences > Encoding tab, "utf8" is entered in the text box; all actions are performed under Linux (Ubunt 12.04) with Meld v1.5.3, Emacs v23.3.1

Current workaround is running in a terminal: dos2unix /path/to/script.r which strips the ^Ms. But this shouldn't be necessary and I'm hoping some one here can tell me how to avoid these.

Cheers.

Answer 1

In a terminal i ran cat script.r | hexdump -C | head and amongst the output returned found a 0d 0a, which is DOS formatting for a new line (carriage return 0d immediately followed by a line feed 0a). I ran the same command on another_script.r i was merging with but only observed 0a, no 0d 0a, indicating Unix formatting.

To check further if this was the source of the ^M line endings, script.r was converted to unix formatting via dos2unix script.r & verified that 0d 0a was converted to 0a using hexdump -C as above. I performed a merge using Meld in attempting to replicate the process which yielded ^M line endings in my script's. I re-oppened both files in Emacs/ESS and found no ^M line endings. Short of converting script.r back to dos formatting and repeating the above procedure to see if the ^M line endings re-appear, i believe i've solved my ^M issue, which simply is that, unbeknownst to me, one of my files was dos formatted. My take home message: in a Windows dominated environ, never assume that one's personal linux environment doesn't contain DOS bits. Or line endings.