querying for memory details in shell

Is there a shell command to know about开发者_Go百科 how much memory is being used at a particular moment and details of how much each process is using, how much virtual memory is left etc?

For "each process", how about top:

PhysMem: 238M wired, 865M active, 549M inactive, 1652M used, 395M free.
VM: 162G vsize, 1039M framework vsize, 124775(0) pageins, 9149(0) pageouts.

PID   COMMAND      %CPU TIME     #TH  #WQ  #POR #MREG RPRVT  RSHRD  RSIZE  VPRVT  VSIZE  PGRP PPID STATE    UID
7233  top          5.7  00:00.53 1/1  0    24   33    1328K  264K   1904K  17M    2378M  7233 3766 running  0  

e.g.:

rprvt  Resident private address space size.
rshrd  Resident shared address space size.
rsize  Resident memory size.
vsize  Total memory size.
vprvt  Private address space size.

Let's also hear it for the old classic, vmstat.

$ vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  0  30160  15884 418680 281936    0    0   406    22    6    3  1  1 93  5

Depends on your operating system. In Linux, free answers two out of your three questions.

~> free
             total       used       free     shared    buffers     cached
Mem:        904580     895128       9452          0      63700     777728
-/+ buffers/cache:      53700     850880
Swap:       506036          0     506036

"Swap" refers to virtual memory.

If you're on Linux, give ps_mem.py a try.

If you are on an up-to-date Linux, cat /proc/$pid/smaps is the business.

If you are on OSX, check https://superuser.com/questions/97235/how-much-swap-is-a-given-mac-application-using.