Question

I want to put an interface down and up every 1 second for 80 times, how can I implement this by a bash script?

Something like this?

COUNT = 80
for n in $(seq -w 1 $COUNT); do
    case $n in   
    [1,3,5,7,9....79]*) # I don't know how to represent the odd value only
       ifconfig veth1 down
       sleep 1
       ;;
    [2,4,6,8,10....80]*)
       ifconfig veth1 up
       sleep 1
       ;;
   esac
done 

Answer 1

COUNT=40
for n in $(seq -w 1 $COUNT); do
  ifconfig veth1 down
  sleep 1
  ifconfig veth1 up
  sleep 1
done

Or if you really want to count to 80:

COUNT=80
for n in $(seq -w 1 $COUNT); do
  case $n in
    *[13579])
     ifconfig veth1 down
     ;;
    *)
     ifconfig veth1 up
     ;;
  esac
  sleep 1
done