Sed is the abbreviation for stream editor. It is used mainly for transforming or altering a line in a file. Inspite of altering it is also used for replacing all/nth occurrence of pattern in a file, altering the slash delimiter, to switch characters with in a line, duplicating lines etc.The file that has to be altered can be directly mentioned in the sed command. It just displays the alteration just on the screen and to apply it to the file the output of the file has to be saved by specifying the location.