Let's break this into its constituent parts:

The date part

• date -u : as explained in man date, the -u flag makes it print the Coordinated Universal Time




• +%V : the data command takes a format argument which is given after a +. For example:

  
  
  

  $ date +%m/%d/%y
  
  05/04/14
  
  

  
  
  

  See man date for a list of all the formats it can produce. The %V means:

  
  
  

  
  

  %V ISO week number, with Monday as first day of week (01..53)

  
  

  
  
  

  So, this week it will return:

  
  
  

  $ date +%V
  
  18
  
  

  
  
  

  And next week it will return 19.




• $(uname) : this will simply print the result of the uname command which should be Linux on a Linux system.

So, putting all that together, the date command will print WeekNumberLinux:

$ date -u +%V$(uname)

18Linux

The sha256sum part

sha256sum simply takes an input string and applies a hashing function to it. This produces a long string that is unique to the input given:

$ date -u +%V$(uname) | sha256sum 

9a93b71d5b2841e649195bc81f8e38600860a040bc368cdbd0cde346b73248a1  -

The sed part

The sed commmand uses the susbtitution operator (s/pattern/replacment/) which will substitute pattern with replacement. In this case, the pattern is W which means "All non-word characters", meaning anything that's not [A-Za-z0-9_], not a letter, not a number and not an underscore. This is used to remove the trailing space and - from the output of sha256sum.

So, the command is a simple way of making sure you are not a robot. Since the date is printing the current week, your output will always be the same until next week when it will change.