Copy the code below into a file. I'm using ~/bin/vnstat-hist.sh. After saving the file mark it as executable using:
chmod a+x ~/bin/vnstat.sh
To run the script call it with the parameter for number of days. For example for today use vnstat-hist.sh 1. For last five days (including today) use:
$ vnstat-hist.sh 5
vnstat -d 5 day summary
2018-04-27 6.21 GiB | 1.83 GiB | 8.04 GiB | 780.45 kbit/s
2018-04-28 5.97 GiB | 1.05 GiB | 7.02 GiB | 681.20 kbit/s
2018-04-29 8.27 GiB | 1.47 GiB | 9.74 GiB | 945.40 kbit/s
2018-04-30 4.09 GiB | 1.35 GiB | 5.44 GiB | 527.97 kbit/s
2018-05-01 1.36 GiB | 1.13 GiB | 2.49 GiB | 315.40 kbit/s
Total:32.73
vnstat-hist.sh Bash script
Note this program can be shorter but hopefully the design is easier to follow for novices.
#!/bin/bash
# NAME: vnstat-hist.sh
# PATH: $HOME/bin
# DESC: Written for AU Q&A: https://askubuntu.com/questions/1030345/get-network-usage-from-specific-date-on-terminal/1030399?noredirect=1#comment1675801_1030399
# Get total vnStat bytes from x days ago to today.
# Parameter 1 = number of days: 1= today, 2= yesterday + today, etc.
# DATE: May 1, 2018.
re='^[0-9]+$'
if ! [[ $1 =~ $re ]] ; then
echo "Error: Parameter 1 must be number of days" >&2; exit 1
fi
# Get body of vnstat -d into file, ie strip headings and total lines
# First get count of all lines, then delete 2 total lines & 5 heading lines
vnstat -d > /tmp/vnstat-hist.txt
NumLines=$(cat /tmp/vnstat-hist.txt | wc -l)
NumLines=$(( NumLines - 2))
cat /tmp/vnstat-hist.txt | head -n $NumLines > /tmp/vnstat-hist2.txt
NumLines=$(( NumLines - 5))
cat /tmp/vnstat-hist2.txt | tail -n $NumLines > /tmp/vnstat-hist.txt
MaxDays=$(cat /tmp/vnstat-hist.txt | wc -l)
DayCount="$1"
(( $DayCount > $MaxDays )) && DayCount=$MaxDays
cat /tmp/vnstat-hist.txt | tail -n $DayCount > /tmp/vnstat-hist2.txt
echo "vnstat -d $DayCount day summary"
awk '{sum+=$8;} END { print "Total:" sum }1' /tmp/vnstat-hist2.txt
# Clean up temp files
rm -f /tmp/vnstat-hist.txt
rm -f /tmp/vnstat-hist2.txt
exit 0