symfony 2 twig limit the length of the text and put three dots
{{ myentity.text|length > 50 ? myentity.text|slice(0, 50) ~ '...' : myentity.text }}
You need Twig 1.6
why not use twig's truncate or wordwrap filter? It belongs to twig extensions and lib is part of Symfony2.0 as i see.
{{ text|truncate(50) }}