Tell the free disk space of a path in megabytes on the command line with one simple command line tool for Windows, Mac OS X and Linux.

sfk diskspace [dirname|-help]
sfk fsinfo [dirname]

show disk space and/or file system informations.
a folder name can be specified which relates
to a specific volume or hard disk.

options
   -byte[s]   all size infos in bytes
   -tab[s]    pure values, tab separated
   -bin[ary]  calculate with binary megabytes
              of 1048576 bytes each.

aliases
   space      same as diskspace
   filesys    same as fsinfo
   freespace  tell only free space

web reference
   http://stahlworks.com/sfk-space

examples
   sfk fsinfo
      tell details about the file system of the
      current directory (.)

   sfk fsinfo D:
      tell about the file system used for drive D:

   sfk space
      tell total and free MB of the current volume.
 
example outputs

  sfk space .

      totalmb=307383 freemb=6057

      just tells the total and free mb available in the volume
      of the current dir.

  sfk fsinfo .

      filesys="NTFS" volume="15234973 EXTDATA" totalmb=307383 freemb=6057

      tells also details of the current filesystem,
      volume ID and label.

  sfk space -bytes -tab +filter -tabform "$col2"

      6057123840

      get only the free space value in bytes. under linux, 
      use -tabform "#col2", or use the unified syntax
      -utabform "#col2" on all platforms.