I am trying to setup syslog-ng to use the DAY and MONTH variable on the source file input.  What am I doing wrong?

source s_file {

file("/psfs_logs/APPSRV_${MONTH}${DAY}.LOG" flags(no-parse));

};

destination d_messages{

udp("10.13.33.11");

};

log {

source(s_file);

destination(d_messages);

};

Any help would be greatly appreciated…