Capturing based on a packet content

Hi,

I'd like to logs all packets that containg a specific pattern (a string in my case). I want to log only thoses packets 24h/7.

Right now, I can log all packets that comes to a specified port and apply a filter, but this generate tons of data on the disk, generating too much data to be usefull.

So I'd like to be able to log using a filter (not logging everything that comes in and then applying a filter).

Is that possible with wireshark?

Thx!