Find

The -exec extension to the find command is a very useful and
flexible utility.

You can use it to get a nice list of all the files in a directory
tree:

find . -type f -exec ll {} \;

or to copy all the files in a directory tree into one, large
directory:

find . -type f -exec cp -p {} /newdir \;

Or say now that you've copied all those files into one directory
there are too many .bak files to delete all at once with the 'rm'
command (yes, that's possible):

find . -name \*bak -exec rm {} \;