How do I escape a single quote in Ruby?

I am passing some JSON to a server via a script (not mine) that accepts the JSON as a string.

Some of the content of the JSON contains single quotes so I want to ensure that any single quotes are escaped before being passed to the script.

I have tried the following:

> irb
> 1.9.3p194 :001 > x = "that's an awesome string"
>  => "that's an awesome string" 
> 1.9.3p194 :002 > x.sub("'", "\'")
>  => "that's an awesome string" 
> 1.9.3p194 :003 > x.sub("'", "\\'")
>  => "thats an awesome strings an awesome string"

but can't seem to get the syntax right.