Bash loops

Executing a Do loop to repeat one command with different hosts

# for num in {1..5}; do ssh host-$num "shutdown"; done
# for host in `cat hosts.txt`; do ssh $host "shutdown"; done
# while read LINE; do COMMAND $LINE; done < FILE

Executing something based on command's output

# for x in $(cmd1) ; do cmd2 $x ; done
# while read x ; do cmd2 $x ; done < $(cmd1)

Executing the same command forever

# while true; do date +%s; done