The ex command g is very useful for acting on lines that match a pattern. You can use it with the d command, to delete all lines that contain a particular pattern, or all lines that do not contain a pattern.
For example, to delete all lines containing "profile" (the first command is optional; it shows the lines that the second command will delete):
More complex patterns can be used, such as deleting all lines that are empty or that contain only whitespace:
To delete all lines that do not contain a pattern, use g!, like this command to delete all lines that are not comment lines in a Vim script:
Note that g! is equivalent to v, so you could also do the above with:
The next example shows use of \| ("or") to delete all lines except those that contain "error" or "warn" or "fail" (:help pattern):