How to update cygwin and installed packages?

[Jeff Gold]

Is there a way to install and update cygwin packages from the command
line?  Something resembling yum on Fedora and apt on Debian and Ubuntu
would be extremely helpful, particularly for setting up a new system.
Manually picking through a list of packages is tedious and error
prone, while a command line with a list of packages can be reliably
pasted from a web page.

I've been trying to find the answer in web searches and the mailing
list archives.  The closest I've come is a brief exchange between
Pawan Taparia and Larry Hall which concludes with a reference to
setup.exe, but as far as I can tell that tool only operates in a
graphical mode.  Giving it options like -h, --help or /h doesn't seem
to provide any documentation.  Have I missed something?  (I've adopted
the same subject in case that helps.)

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