Bash function to nicely output the elapsed time

The bash function:

### Function: take integer UNIXTIMESTAMP start calc the diff against the current "date +'%s'". Displays elapses timestamp as "HH:MM:SS (NNN sec)"

function printelapsed() {

    local let s=$((`date +'%s'`-$1))

    ((all=s, sec=s%60, s/=60, min=s%60, hrs=s/60))

    printf "%d:%02d:%02d (%d sec)" $hrs $min $sec $all

} ### end func

The code usage:

let STARTSTEP=$(date +'%s')   ### Start the timer

#### DO SOME STUFF HERE ###

echo "[`date +"%Y-%m-%d %H:%M:%S"`] Elapsed: `printelapsed $STARTSTEP`." >> $LOGFILE

The output:

[2018-11-01 02:51:40] Total elapsed: 0:06:39 (399 sec).