[ubuntu] Question Regarding Easy Linux command

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http://ubuntuforums.org – So I'm working on a little project. I like writing to-do lists in plain text editors, labeled as Today.txt and so on. I want to be able to create an updated "Current_ToDo" through (in a terminal). This is my first step: cat 8_16 8_17 > CurrentTodo So, suppose there's another list, 8_15 , which has some of the same tasks as 8_16 and 8_17 (unfinished tasks that go into CurentToDo), but also there is some other task that was not completed. How do I search for this string? What terminal command can search for that third string (the other task, let us say z), distinguish it fr (Hardware)