Exit codes for feed executables

Hi,

I am writing bash script for updating greenbone feeds to use in crontab.I need a exit codes or a value something equal for understanding feed is up to date or not.If it is possible how/where can i get this value after execute them.

greenbone-certdata-sync
greenbone-nvt-sync
greenbone-scapdata-sync

I am looking something like that;

Exit code 0: all new updates were installed.
Exit code 1: we were already up-to-date.
Exit code 3: some updates were installed, but some weren’t.
Any other exit code indicates failure.

Thanks.