Why can't I view view log files with cat/grep/etc? (clog)

From PFSenseDocs

pfSense uses a Circular Log format to maintain a constant log size. There are multiple benefits to this method, mainly that the log files cannot grow and fill up your filesystems. The downside is that they are no longer plain text logs, and cannot be directly used by programs like cat or grep. If you view them, you may see "random" binary data inside the log.

In order to view these files from the shell, you must use the "clog" command, like so:

clog /var/log/filter.log

You can then pipe the output to tools like grep if you desire.

In order to follow the log files in a manner like "tail -f" would allow, use:

clog -f /var/log/filter.log

The contents of the log will be printed to the console, and then new entries will appear as they are written.