musage

#!/usr/bin/env bash
# Print the Resident Set Size memory usage of a process with given PID
# in a human readable format.
#
# Usage:
#
#   musage <PID>           # take the process by ID
#   musage <PROCESS-NAME>  # take the newest process that matches the given name
#
# Examples:
#
#   musage 12345
#   musage firefox
#
# author: andreasl
int_re='^[0-9]+$'
if [[ "$1" =~ $int_re ]]; then
    pid="$1"
else
    # the subshell containing the `pgrep` below is itself a matching process, filter it out
    pids_str="$(pgrep --full "$1")"
    mapfile -t pids <<<"$pids_str"
    [ "${#pids[@]}" -lt 2 ] && {
        >&2 echo "Error: Found no process matching \"${1}\"."
        exit 1
    }
    pid="${pids[-2]}"
fi

# shellcheck disable=SC2016
awk_script='
{
    split("KB MB GB TB", units);
    for (i = 1; $1 >= 1024 && i; i++) {
        $1 = $1 / 1024;
    }
    printf "%.2f %s\n", $1, units[i];
}'

ps -o rss= -p "$pid" | awk "$awk_script"