Exclude from log by pattern matching
The command grep -v allows filtering out a term or regex from the input. You can use a pipe (|) to combine multiple grep -v commands.

Example: grep -v firewall /var/log/system.log | grep -v imagent | grep -v mdworker

The first grep command in this example operates on the file contents; the subsequent grep commands operate on the output of the previous grep command.

grep is located at /usr/bin/grep on my Lion system. For more information on using grep, read the man page with the command man 1 grep or just man grep.



Edit: Command line can be shortened to

grep -v 'firewall\|imagent\|mdworker' /var/log/system.log