How do you specify a gem's dependency on a unix program, e.g. fmt or tidy?

How do you specify in a gem's gemspec that the gem assumes that "fmt" or "tidy" is installed on the system? These are uni开发者_StackOverflow中文版x tools and not Ruby gems.

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This is another place where rubygems just lacks...

A few workarounds:

put a message about it in the post_install message

check for it at runtime

check for it at install time by using a fake mkrf_conf.rb http://en.wikibooks.org/wiki/Ruby_Programming/RubyGems#How_to_install_different_versions_of_gems_depending_on_which_version_of_ruby_the_installee_is_using

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You can use the requirements attribute. It doesn't actually enforce the dependency, but it looks like the right place to put the information.

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Put it in the README and hope people read it. ;)