Determining the differences between the current version and a vi swap file

When I attempted to edit a file, index.php, using the vi editor, I saw the following message:

E325: ATTENTION
Found a swap file by the name ".index.php.swp"
          owned by: joe   dated: Mon Feb 20 19:36:11 2017
         file name: ~joe/www/UVNC/index.php
          modified: YES
         user name: joe   host name: example.com
        process ID: 19776
While opening file "index.php"
             dated: Mon Feb 20 19:38:44 2017
      NEWER than swap file!

(1) Another program may be editing the same file.  If this is the case,
    be careful not to end up with two different instances of the same
    file when making changes.  Quit, or continue with caution.
(2) An edit session for this file crashed.
    If this is the case, use ":recover" or "vim -r index.php"
    to recover the changes (see ":help recovery").
    If you did this already, delete the swap file ".index.php.swp"
    to avoid this message.

Swap file ".index.php.swp" already exists!
[O]pen Read-Only, (E)dit anyway, (R)ecover, (D)elete it, (Q)uit, (A)bort:

I hit the q key to return to the Bash shell prompt. When I compared the time stamps on the current version of the file and the .swp file, I saw that the current version had a time stamp 2 minutes after the time stamp for the .swp file.

$ ls -al | grep 'index.php'
-rw-rw-r--. 1 joe joe   7571 Feb 20 19:38 index.php
-rw-r--r--. 1 joe joe  20480 Feb 20 19:36 .index.php.swp
$

Note: you need to use the -a option with the ls command, since any files that have a name beginning with a period are hidden by default and not displayed by the command unless that option is used.

I wanted to know what the difference was between the .swp version and the current version to determine if I might should recover the file from the .swp version. But you can't just use the diff utility to perform a comparison of the two files to determine their differences, since the .swp file is a binary file.

But, I can choose R for recover when opening the file and then write the contents of the file out to another file, e.g., I could use :w temp.php and then :q! to quit without saving the file. I can then compare the two files with the diff command.

$ diff index.php temp.php
208,210c208,209
< via VNC for remote administration and also still use the
< <a href="https://en.wikipedia.org/wiki/File_transfer" rel="nofollow">file
< transfer</a> capability provided in UltraVNC.</p>
---
> via VNC for remote administration and also still use the file transfer
> capability provided in UltraVNC.</p>
$

I can, in this case, see I made only one small change to the file that is contained in the index.php file, but not the

.index.php.swp

file, so I don't need the .swp file and can delete it along with the temporary file I created for performing the comparison.