Seems have to download svn to get only one file.
False.
It's not that long of a page you were linked to. If you read just a *little* bit further, you'd see other options. You were even given a indication that there'd be more than one option when you were directed to that page.
]]>It is also possible to get this PKGBUILD file from package detail like from this page:
https://www.archlinux.org/packages/extr … 4/libupnp/
On top right go to Package Actions - Source Files
Then you can find PKGBUILD file.
There are various ways to obtain the PKGBUILD for a given package; https://wiki.archlinux.org/index.php/Arch_Build_System explains all of this.
]]>