How do I make a very basic file filter using grep?

A really simple question, but I couldn't find a simple answer here on SO.

I have a log file my.log where some lines contain the word "User". How can I make a grep command to run constantly and output every time the log is updated with开发者_如何学Python a line containing the word "User"? Thanks.

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tail -f my.log | grep User

tail -f watches the file and outputs any lines added to the end

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You're right, it's simple:

tail -f my.log | grep "User"