I tried that but I am getting:
pkg_add -r snort
Fetching ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-8.1-release/Latest/snort.tbz… Done.
pkg_add: warning: package 'snort-2.8.5.3_1' requires 'pcre-8.02', but 'pcre-8.10' is installed
=========================================================================
Snort uses rcNG startup script and must be enabled via /etc/rc.conf
Please see /usr/local/etc/rc.d/snort
for list of available variables and their description.
Configuration files are located in /usr/local/etc/snort directory.
NOTE: Starting with Snort 2.4.0 (released on 2005-04-22)
the rules are no longer included with the distribution.
Please download them from http://www.snort.org/rules/.
You might consider installing security/oinkmaster port to simplify
rules downloads and updates.