Grep para la subcadena
output=$(command)
[[ $output =~ (CpuIowait=[0-9][.][0-9]{2}) ]] && echo "${BASH_REMATCH[1]}"
Hungry Hippopotamus
output=$(command)
[[ $output =~ (CpuIowait=[0-9][.][0-9]{2}) ]] && echo "${BASH_REMATCH[1]}"