[Freeswitch-users] call duration for bash script

hello freeswitch-users, i would like to run a bash script after a call and for this script i need the duration of that call. i found the variable "billsec", but i couldn´t find any dialplan examples how to use this variable. can someone give me a hint how i can hand over the duration of the call to a bash script in the dialplan. thank you very much! best regards, thomas