bash

• get the size of a directory on the command line?: du -sh is a good place to start. The options are (from man du):

    -s, --summarize
      display only a total for each argument
    -h, --human-readable
      print sizes in human readable format (e.g., 1K 234M 2G)
  

• create symbolic link 2015/10/23 19:21:38

    ln -s source_file target_file(symbolic_link)
  

• count files in a directory

    ls -l directory_name | wc -l