Mac - how to delete all files NOT of a specific type

Question

On Unix or Mac:

How do you delete all files NOT of a specific type. Or How to copy all files of a specific type with the containing folder.

Thanks

Answer 1

Use find, e.g. to delete all files which are not .txt files:

$ find . -type f -not -name \*.txt -exec rm -f {} \;

WARNING: use this kind of command with care as it's easy to delete a lot of files unintentionally. Do a "dry run" first if you're not confident, e.g. to preview the above command:

 $ find . -type f -not -name \*.txt -exec echo "Delete {}" \;