sed execution with input from keyboard

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http://www.unix.com – > sed '' Hello hi Hello output How hi output ^D How > sed should take each line as input, process and output the result. In the above scenario the input is passed from keyboard and the output of 'Hello' as you can see is displayed on the screen after 'hi' is passed as input but not as soon as we passed 'Hello'. Why?:wall: (HowTos)