Build a table from a list by comparing existing table entries

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http://www.unix.com – I am new to this shell scripting.... I have a file which contains list of users. This files get updated when new user comes into the system. I want to create script which will give a table containing unique list of users. When I say unique, it means script should match table while parsing user file list. E.g. List----- User1 User2 User1 User3 User4 User1 The script output should be a list with User1 User2 User3 User4 Thanks (HowTos)