OS X (Apple)

top -l1 -o RSIZE | sed 1,12d | awk '{print $11}' | sed -e 's/[+,-]//g' -e 's/K//g' -e 's/M/*1024/g' | bc
  | awk '{RAM+=$1} END {printf "\nProcesses RAM:\t%.2fGB\n",RAM/1024/1024}';
active=`vm_stat | grep ' active' | awk '{print $3}'`;
wired=`vm_stat | grep wired | awk '{print $4}'`;
echo   $wired $active | awk '{printf "RAM Usage:\t%.2fGB\n\n",($1+$2)*4096/1024/1024/1024}'

time cat bigfile > /dev/null
time cat bigfile > /dev/null

b=0; while [ $b -eq 0 ]; do ps -A >> Desktop/file; if [ `du -d0 Desktop/file | awk '{print $1}'` -gt 204800 ]; then b=1; fi; done

~ $ du -d0 -h Documents/Programación/Flash/Movement/Goma.fla; time cat Documents/Programación/Flash/Movement/Goma.fla > /dev/null 
 50M	Documents/Programación/Flash/Movement/Goma.fla

real	0m0.132s
user	0m0.002s
sys	0m0.023s
~ $ du -d0 -h Documents/Programación/Flash/Movement/Goma.fla; time cat Documents/Programación/Flash/Movement/Goma.fla > /dev/null 
 50M	Documents/Programación/Flash/Movement/Goma.fla

real	0m0.012s
user	0m0.001s
sys	0m0.011s
~ $