(1) pkg_* can't handle absolute paths, so use two @cwd's and relative paths
throughout.
(2) pkg_* can't handle FIFOs, so use mkfifo to create it and rm to delete it.
(3) pkg_* can't handle empty directories, so create them with mkdir.
(4) the @mode/@owner/@group directives don't appear to work so use @exec
to set all the modes.
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