I assume that you are trying to get a list of all files under c:/tmp except everything that is in (and including) the c:/tmp/logs folder:
files = FileList.new("c:/temp/**/*").exclude(/c:\/temp\/logs/)
[Edit] For more information, see the FileList#exclude documentation. For example, to exclude multiple directories, you can either add multiple string / regex arguments, change the regular expression to match all directory patterns that need to be excluded, or do something similar in a block.
x1 = /c:\/temp\/logs/
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