As we have discussed about vnstat installation on previous post, the following shell script will help you to install in your system (CentOS / Fedora / RHEL) automatically, 

Create a file with the name of vnstat-installation.sh and give execute permission,
 

#  vim vnstat-installation.sh

# chmod +x vnstat-installation.sh

Shell Script:
 
### VNSTAT Installation Shell Script ###

#!/bin/sh
### Get active interface
ETHDEV_NAME=`ip link show | grep 'state UP' | awk '{print $2}' | cut -d ':' -f1`

###  Find out whether vnstat  installed or not
VNSTAT_PATH=`whereis vnstat | awk '{print $2}'`

    if [ ! -f $VNSTAT_PATH ]; then

### Find 64 bit or 32 bit and install rpm repo
            if $(getconf LONG_BIT | grep '64'); then
                rpm -Uvh http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm
               else
                rpm -Uvh http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.i686.rpm
            fi
### Install vnstat package using yum command
            yum install vnstat -y
            vnstat -u -i  $ETHDEV_NAME
### Set cron job 
            echo "00 12 * * * /usr/bin/vnstat -u" >> /var/spool/cron/root
            /etc/init.d/crond restart
###Get vnstat Version
            vnstat -v
    else
            echo "VNSTAT Package Installed in your system."
    exit;
    fi

Execute the script,
 
# ./vnstat-installation.sh

or

#  sh ​vnstat-installation.sh

Download Script