[symfony] symfony 2 twig limit the length of the text and put three dots

I know this is a very old question, but from twig 1.6 you can use the slice filter;

{{ myentity.text|slice(0, 50) ~ '...' }}

The second part from the tilde is optional for if you want to add something for example the ellipsis.

Edit: My bad, I see the most up-voted answer do make use of the slice filter.