If you are using linux,You usually use a "free" command to find physical memory ie RAM details on the system
output = %x(free)
output will look slightly like the following string
" total used free shared buffers cached\nMem: 251308 201500 49808 0 3456 48508\n-/+ buffers/cache: 149536 101772\nSwap: 524284 88612 435672\n"
You can extract the information you need using simple string manipulations like
output.split(" ")[7] will give total memory
output.split(" ")[8] will give used memory
output.split(" ")[9] will give free memory