Dangers of the sed Quit Command (Unix Power Tools, 3rd Edition)

34.23. Dangers of the sed Quit Command

The sed quit command, q (Section 34.22), is very useful for getting sed to stop processing any more input once you've done what you want.

However, you need to be very careful not to use q in any sed script that writes its edits back to the original file. After q is executed, no further output is produced. It should not be used in any case where you want to edit the front of the file and pass the remainder through unchanged. Using q in this case is a dangerous beginner's mistake.

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34.22. Uses of the sed Quit Command		34.24. sed Newlines, Quoting, and Backslashes in a Shell Script