That's the Schwartzian Transform. I goes something like this:

</var/script/proc/*> will glob and return the list of file/directories in that folder.
each element is mapped into an array ref[ ] containing the original string and the last modified date -M
the list is sorted by the modification date which is the second element of the array ref, hence $a->[1]
then the first element of the array (which is the original folder name) is retrieved $_->[0] with another map

So in short, you get the list of folders, you build an array of arrays containing the folder name and the modification date, you sort by the modification date, and return only the folder names to use.

Update: :)

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