Diff on linux with lots of files

This is a post to record difference methods on linux or wherever for large numbers of files (3m to 4m)

https://stackoverflow.com/questions/4997693/given-two-directory-trees-how-can-i-find-out-which-files-differ

A utility that is useful for such compares is xargs.  A tutorial is below

http://www.linuxplanet.com/linuxplanet/tutorials/6522/1

Example with xargs and LS with find

Prototype for doing very large searches, with xargs opening the length of the environment to huge

find . -name "*.*" -size +1024k -print | xargs /bin/ls -lrt

find . -name "*.*" -size +1024k -exec ls -lrt {} \;

Second example does example with ls passing individual files.

http://www.unix.com/unix-for-dummies-questions-and-answers/77947-help-run-ls-command-along-find-command.html