How to check directory size/disk space usage on mac os x/linux, from the command line

You can use du(disk usage) command line tool:

Dushans-MacBook-Air:projects dushan$ du -hs s3cms/ 
921M s3cms

‘h’ is for human readable output, eg. M for megabytes, and ‘s’ is for summarized output(do not display size of subdirectories or specific files within directory).