How can I display the memory usage of each process if I do a 'ps -ef'?

@user26528's answer doesn't quite calculate the memory correctly - you need the sum of the mappings in smaps, not just the top one. This script should do it:

#!/bin/bash

for pid in $(ps -ef | awk '{print $2}'); do
    if [ -f /proc/$pid/smaps ]; then
        echo "* Mem usage for PID $pid"     
        rss=$(awk 'BEGIN {i=0} /^Rss/ {i = i + $2} END {print i}' /proc/$pid/smaps)
        pss=$(awk 'BEGIN {i=0} /^Pss/ {i = i + $2 + 0.5} END {print i}' /proc/$pid/smaps)
        sc=$(awk 'BEGIN {i=0} /^Shared_Clean/ {i = i + $2} END {print i}' /proc/$pid/smaps)            
        sd=$(awk 'BEGIN {i=0} /^Shared_Dirty/ {i = i + $2} END {print i}' /proc/$pid/smaps)
        pc=$(awk 'BEGIN {i=0} /^Private_Clean/ {i = i + $2} END {print i}' /proc/$pid/smaps)
        pd=$(awk 'BEGIN {i=0} /^Private_Dirty/ {i = i + $2} END {print i}' /proc/$pid/smaps)
        echo "-- Rss: $rss kB" 
        echo "-- Pss: $pss kB"
        echo "Shared Clean $sc kB"
        echo "Shared Dirty $sd kB"
        echo "Private $(($pd + $pc)) kB"
    fi
done

ps ef -o command,vsize,rss,%mem,size

I could not find an option for shared memory, but I did find options for % of total physical memory and the amount of swapspace that would be needed to swap out the process. This and much more is documented in the man page for ps.

List processes by memory usage

ps -e -orss=,args= | sort -b -k1,1n