How to match a pattern and output its line followed by multiple lines up to an empty line

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Question

Context option -A NUM (--after-context=NUM) outputs a fixed number NUM of lines after a matching line.

However, what I want is to match a line and output it followed by all lines up to the first empty line.

See also #369 by @vt-alt and also Q&A #371 to match a block of lines (similar)

Answer

Use lazy quantifiers in the regex to match a PATTERN followed by lines up to pattern \n\n that matches an empty line:

$ ug -o '.*PATTERN(.|\n)*?\n\n' file.txt

where (.|\n)*? lately matches anything up to the \n\n that follow in the regex. Option -o only shows what matches. Otherwise, the second \n in \n\n triggers a match of the line after, which is the remainder of the matching lines that comes after till the next \n, which is exactly like how all other line matching is done to show the remainder of a line after a match in that line.

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Note: see answer in the question post.