There is a method provided in rails to convert a string to the camel case.
The method is camelize.

By default camelize converts a string to upper camel case. If we don't specify any argument in camelize method, it will convert the given string to upper camel case.

ex:-

2.1.5 :003 > a = "hello_world".camelize
 => "HelloWorld" 

If we want to print the string in lower CamelCase(i.e first character in lower case and first character of other Consecutive words in upper case) then we can pass a lower parameter to the camelize method.

ex:-

 2.1.5 :002 > "hello_world".camelize(:lower)
 => "helloWorld"

If a string is to be converted to the snake case we can use the underscore method provided by Rails. The underscore method converts a string to snake case(i.e words seperated with _)

2.1.5 :010 > "HelloWorldTest".underscore
 => "hello_world_test"