Mac Terminal "find" command : What does a double slash in the result output mean?
find is rather literal. When you tell it to search within "~/Downloads/", it uses that (including the trailing slash) as the prefix for whatever it finds. Since there's an unnecessary and irrelevant slash at the end of the path you gave it, you wind up with an unnecessary and irrelevant extra slash in the output.

Solution: remove the trailing "/" from the search directory:

#&gt; find ~/Downloads/ -iregex ".*some.*"
/Users/michael/Downloads//subDirectory/some_file.pdf
#&gt; find ~/Downloads -iregex ".*some.*"
/Users/michael/Downloads/subDirectory/some_file.pdf