flag=true
read -p "please input a number:" num
while $flag
do
   expr $num + 0 >/dev/null
   [ $? -eq 0 ]  flag=false || read -p "please input a integer:" num
done

flag=true
read -p "please input a number:" num
while $flag
do
  len=`echo "$num"|sed 's/[0-9]//g'|sed 's/-//g'`
  [ -n $len ]  flag=false || read -p "please input a integer:" num
done