vbin has a very useful command called sav.

You always need to make a backup copy of a file before messing with it.  A simple

   $ cp book.xml -p book.xml.sav

will do.  The -p preserves the original date and ownership of the file.

sav does this for you. In other words:

   $ sav book.xml
   cp -p book.xml book.xml.sav

Its that’s simple.  Its just a convenient way to make a quick backup before you edit something.  If you want to see the changes since you backed it up, you can use savdiff:

   $ savdiff book.xml
   diff book.xml.sav book.xml

If you want to revert back you can use unsav:

   $ unsav book.xml
   cp -p book.xml.sav book.xml