Reverse

$ gem install reverse

Usage: reverse [options]
    -V, --verion                     Show version number and quit
    -v, --verbose                    Verbose Mode (IP Address with reverse DNS)
        --no-color                   No Color Mode

$ cat /var/log/maillog | reverse
$ tail -f /var/log/maillog | reverse
$ grep Accepted /var/log/secure | reverse -v