Monitor RAM usage and runtime of a previously started process (using ugly hardcoding)

monitor_process_ram.zsh

#! /usr/bin/zsh

if [[ $# = 0 ]]; then
    echo "Usage: $0 PID [INTERVAL]"
    exit
fi


pid=$1
pgid=$(ps -o pgid= $pid)
pgid=${pgid//[[:space:]]/}

interval=${2:-0.1}


_size() {
    numfmt --to=iec-i --suffix=B --from-unit=1Ki --format="%10.1f" $1 |
        sed -e 's/\([0-9.]\+\)\([a-zA-Z]\+\)/\1 \2/'
}

_cr="\r\033[K"


peak_rss=0
while info=($(/bin/ps -o pid=,rss=,etime= -$pgid)); do

    # sum up current RSS from all process in the process group:
    cur_rss=0
    for i in $(seq 2 3 $#info); do
        (( cur_rss += $info[$i] ))
    done

    # determine current elapsed wall time:
    for i in $(seq 1 3 $#info); do
        if [[ $info[$i] = $pid ]]; then
            cur_time=$info[$i+2]
        fi
    done

    # update peak value:
    if (( $cur_rss > $peak_rss )); then
        peak_rss=$cur_rss
    fi

    echo -n "${_cr}Time: $cur_time      peak rss: $(_size $peak_rss)     cur rss: $(_size $cur_rss)"

    sleep $interval
done
    echo    "${_cr}Time: $cur_time      peak rss: $(_size $peak_rss)     FINISHED"