> From windows to/from attu:

 Winscp OR
 Filezilla OR whatever your favorite graphical scp/sftp client 
 Running cygwin use scp or sftp

> From mac to/from attu:

 scp or sftp at terminal

> From Virtual machine to/from attu:

 scp or sftp at terminal OR
 view attu directory in file browser - mount attu home dir

> From Virtual machine to/from local machine:

 drag and drop to/from the vm to desktop

> From attu from a URL

 wget - to get a file from a url

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For more info look at the slides linked on the homework page:

http://www.cs.washington.edu/education/courses/cse390a/13sp/handouts/MovingAndEditingFiles_12sp.pdf