–dry-run option to check that the patch applies cleanly. It can be a real pain to pull out a partially-applied patch. The -p1 option strips off part of the diff file’s pathnames for each changed file (see the patch(1) manpage for more details). Now you’ve checked that it should apply cleanly, run the following to actually apply it. Then you’re done!

Copied from : http://linuxpoison.blogspot.com/2007/12/...ource.html