Ruby中检测Gem是否安装的方法

#!/usr/bin/env ruby
# encoding: utf-8

def checkGemAvailable(gemName, versionLimit=nil)
    isAvailable = false
    begin
        if versionLimit == nil
            gem  gemName
        else
            gem  gemName, versionLimit
        end
        isAvailable = true
    rescue LoadError
    end
    isAvailable
end

puts checkGemAvailable('rack')
puts checkGemAvailable('rack', '>=2')

rack (1.5.2)

true
false