relative time in shell (awk)

relative_time.sh

#!/user/bin/env bash

# run as ./relative_time 2021-05-06T20:37:59Z

relative_time() {
  declare -r dt="$1"
  declare ts_then ts_now retval

  ! { ts1=$(date +%s -d "${dt}"); retval=$?; }

  test "${retval}" -eq 0 || return

  ts2=$(date +%s)

  awk -v ts1="${ts1}" -v ts2="${ts2}" '
    BEGIN {
        diff = ts2 - ts1;
        if (diff < 0) { print "not yet happened"; exit; };
        if (diff > (24*60*60)) printf "%.0f days ago\n", diff/(24*60*60);
        else if (diff > (60*60)) printf "%.0f hours ago\n", diff/(60*60);
        else if (diff > 60) printf "%.0f minutes ago\n", diff/60;
        else printf "%s seconds ago\n", diff;
    }'
}

relative_time "$1"