Nagios Log File Time Conversion [Human Readable]

To tail the file online:

tail -f /var/log/nagios3/nagios.log | perl -pe 's/(\d+)/localtime($1)/e'

To convert certain time stamp:

echo 1376930831 | perl -pe 's/(\d+)/localtime($1)/e'
Mon Aug 19 19:47:11 2013