ruby2.5-dev - 2.5.5-3+deb10u4 main

Ruby is the interpreted scripting language for quick and easy
object-oriented programming. It has many features to process text
files and to do system management tasks (as in perl). It is simple,
straight-forward, and extensible.
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This package contains the header files and the mkmf library, necessary
to make extension library for Ruby 2.5. It is also required to build
many gems.