You can use the send method to call a method with the same name as the specified symbol:

send1.rb

name = "Fred"
puts( name.send( :reverse ) )    #=> derF
puts( name.send( :upcase ) )     #=> FRED

Although the send method is documented as requiring a symbol argument, you can also use a string argument. Or, for consistency, you could use to_sym to transform the string to a symbol and then call the method with the same name as that symbol:

name = MyString.new( gets() )
methodname = gets().chomp.to_sym #<= to_sym is not strictly necessary
name.send(methodname)

Here is a working example of using send to execute a named method entered at runtime:

send2.rb

class MyString < String
    def initialize( aStr )
        super aStr
    end

    def show
        puts self
    end

    def rev
        puts self.reverse
    end
end

print("Enter your name: ")          #<= Enter: Fred
name = MyString.new( gets() )
print("Enter a method name: " )     #<= Enter: rev
methodname = gets().chomp.to_sym
puts( name.send(methodname) )       #=> derF