Are there websites that allow one to search for which package contains a particular file?

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http://unix.stackexchange.com – I want to write some generic instructions on how to find the package that installs a particular file (the exact context is TeX packages: find the package in the Unix distribution that contains a particular TeX package). I might not know the precise path but will know the exact file name. Ubuntu has the package search facility which allows me to do precisely this: search for the packages containing a particular file. Which other Unix distributions have the same online search capability, and where are they? (I found a few related questions, but none seemed to give the answer I'm looking for (HowTos)