You're going to want to use Object#send, but you'll need to call it with the correct casing. For example:
[1,2,3].send('length')
=> 3
Edit: Additionally, though I would hesitate recommend it because it seems like bad practice that will lead to unexpected bugs, you can deal with different casing by searching through a list of methods that the object supports.
method = [1,2,3].methods.grep(/LENGth/i).first
[1,2,3].send(method) if method
=> 3
We grep through all methods using a case-insensitive regex, and then send the first returned symbol to the object if any was found.
