glen, are the owner of the directory (see the
. file in your listing). A directory is just a list of files and you have the permission to alter this list (e.g. add files, remove files, change ownerships to make it yours again, etc.). You may not be able to alter the contents of the file directly, but you can read and unlink (remove) the file as a whole and add new files subsequently.1 Only witnessing the before and after, this may look like the file has been altered.
Vim uses swap files and moves files around under water, so that explains why it seems to write to the same file as you do in your shell, but it's not the same thing.2
So, what Vim does, comes down to this:
cat temp > .temp.swp # copy file by contents into a new glen-owned file
echo nope >> .temp.swp # or other command to alter the new file
rm temp && mv .temp.swp temp # move temporary swap file back
1This is an important difference in file permission handling between Windows and Unices. In Windows, one is usually not able to remove files you don't have write permission for.
2 update: as noted in the comments, Vim does not actually do it this way for changing the ownership, as the inode number on the
temp file does not change (comaring
ls -li before and after). Using
strace we can see exactly what
vim does. The interesting part is here:
open("temp", O_WRONLY|O_CREAT|O_TRUNC, 0664) = -1 EACCES (Permission denied)
unlink("temp") = 0
open("temp", O_WRONLY|O_CREAT|O_TRUNC, 0664) = 4
write(4, "more text bla\n", 14) = 14
close(4) = 0
chmod("temp", 0664) = 0
This shows that it only unlinks, but does not close the file descriptor to
temp. It rather just overwrites its whole contents (
more text bla\n in my case). I guess this explains why the inode number does not change.