Bash script, get current uplink/downlink usage?

I am using a script that will run speedtest and store results (ping, download speed, upload speed) to a Google Sheet through IFTTT.
I think it would be wise to store what is the bandwidth usage (up/down) right before the test, as the speedtest results may be altered as for other process consuming bandwidth at the same time.
Is there a command that can be run from a script to get these values?

you'll have to decide on what kind of hysteresis is acceptable to you....

iftop ( basic usage )

iftop -i eno1 -t -s 5 | grep Peak