Red Hat

[test]$ free -m
             total       used       free     shared    buffers     cached
Mem:        129176      92753      36423          0       2268      39973
-/+ buffers/cache:      50511      78664
Swap:        31996          0      31996

[test ~]$ top
top - 12:31:48 up 7 days,  1:26,  3 users,  load average: 0.75, 1.12, 1.20
Tasks: 995 total,   1 running, 994 sleeping,   0 stopped,   0 zombie
Cpu(s):  3.3%us,  1.2%sy,  0.0%ni, 95.4%id,  0.0%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:  132276504k total, 94983252k used, 37293252k free,  2322436k buffers
Swap: 32764556k total,        0k used, 32764556k free, 40933180k cached

free -m | awk '/buffers.cache/ {print $4}'
top | awk '/^Mem: / {print $8}'