Install specific versions of a library from Homebrew

specific_version_of_library_in_homebrew.sh

#substitute LIBNAME for the library you want. Eg: grails

brew tap homebrew/versions
brew versions LIBNAME
#2.1.2    git checkout 5c5b964 /usr/local/Library/Formula/grails.rb   # <== we want this version
#2.1.3    git checkout d08ef78 /usr/local/Library/Formula/grails.rb
#2.1.1    git checkout 1bcf5af /usr/local/Library/Formula/grails.rb
#...
cd /usr/local
git checkout 5c5b964 Library/Formula/LIBNAME.rb   # <== notice the hash, it's a reference to the version we want
cd -
brew install LIBNAME