Bandwidth Exceeded Server Auto-Shutdown

#!/bin/bash
ax=`vnstat --oneline | awk -F ";" '{print $11}'`
if [[ "$ax" == *GiB* ]]
then
    if [ $(echo "$(echo "$ax" | sed 's/ GiB//g') > 900"|bc) -eq 1 ]
    then
      shutdown -h now
    fi
fi