tail -f /logs/mail.log | sed -e '/last message repeated/d' -e 's/message forwarded from myhost: //i'

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tail -f /logs/mail.log | awk '$4~/host/ { print }'

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(while true ; do uptime ; sleep 3 ; done) | perl -ne '@load =  /\d\.\d\d/g ; print "\a" if $load[0] < .4 ; print "@load\n"'