Purging disk cache to see mor free RAM on Mac OS X

It is frightening when there is little amount of free RAM displayed by top command.

Most of time on an idle mac it can be fixed by purge command (to force disk cache to be purged).

sudo purge # do not use. see important note below

On GNU/Linux there is another way round (as usual).

sudo -s

echo 3 > /proc/sys/vm/drop_caches

Important update!!
Do not use sudo purge  on Mac OS X!
it turned out it is dangerous. Just reboot the Mac.