Run diff command to compare all files in directory

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http://askubuntu.com – I have two folders having in theory an identical folder structure and the same files. I wish to check for differences between the two copies in the two folders. I can run diff folder1/file1 folder2/file1 one by one but this is time consuming. Is there a way to identify which are the files which differ in the two folders? If not is there at least a way to compare the contents of a folder with the contents of the second folder? (HowTos)